Undocumented Matlab » FindJObj

Uitable cell colors

Yair Altman — Thu, 27 Oct 2011 01:51:53 +0000

A client recently asked me to develop an application that will help discover technical indicators for trading on the stock market. The application was very data-intensive and the analysis naturally required visual presentations of number-crunching results in a readable manner. One of the requirements was to present numeric results in a data table, so we naturally use uitable for this.

Today I will show how using some not-so-complex Java we can transform the standard Matlab uitable into something much more useful.

First pass – basic data table

We start by displaying the data in a simple uitable. The essence of the relevant code snippet was something like this:

headers = {'Periods', ...
           'Any period
returns', ...
           'Avg return
signal', ...
           'Avg
gain', ...
           'Avg
draw', ...
           'Gain/draw
ratio', ...
           'Max
gain', ...
           'Max
draw', ...
           'Random
% pos', ...
           'Signal
% pos', ...
           'Payout', '% p-value'};
hTable = uitable('Data',data, 'ColumnEditable',false, ...
           'ColumnName',headers, 'RowName',[], ...
           'ColumnFormat',['numeric',repmat({'bank'},1,11)], ...
           'ColumnWidth','auto', ...
           'Units','norm', 'Position',[0,.75,1,.25]);

Plain data table - so boooooring...

We can see from this simple example how I have used HTML to format the header labels into two rows, to enable compact columns. I have already described using HTML formatting in Matlab controls in several articles on this website. I have not done this here, but you can easily use HTML formatting for other effect such as superscript (^{), subscript (_{), bold (), italic (), font sizes and colors () and other standard HTML effects.}}

Even with the multi-line headers, the default column width appears to be too wide. This is apparently an internal Matlab bug, not taking HTML into consideration. This causes only part of the information to be displayed on screen, and requires the user to either scroll right and left, or to manually resize the columns.

Second pass – auto-resizing that actually works…

To solve the auto-resizing issue, we resort to a bit of Java magic powder. We start by using the findjobj utility to get the table’s underlying Java reference handle. This is the containing scrollpane, and we are interested in the actual data table inside. We then use the setAutoResizeMode, as described in the official Java documentation.

jScroll = findjobj(hTable);
jTable = jScroll.getViewport.getView;
jTable.setAutoResizeMode(jTable.AUTO_RESIZE_SUBSEQUENT_COLUMNS);

Auto-resized columns that actually work

Third pass – adding colors

There are still quite a few other customizations needed here: enable sorting; remove the border outline; set a white background; set row (rather than cell) selection and several other fixes that may seem trivial by themselves but together giver a much more stylish look to the table’s look and feel. I’ll skip these for now (interested readers can read all about them, and more, in my detailed uitable customization report).

One of the more important customizations is to add colors depending on the data. In my client’s case, there were three requirements:

data that could be positive or negative should be colored in green or red foreground color respectively
large payouts (abs > 2) should be colored in blue
data rows that have statistical significance (%p-value < 5) should have a yellow background highlight

While we could easily use HTML or CSS formatting to do this, this would be bad for performance in a large data table, may cause some issues when editing table cells or sorting columns. I chose to use the alternative method of cell renderers.

ColoredFieldCellRenderer is a simple table cell renderer that enables setting cell-specific foreground/background colors and tooltip messages (it also has a few other goodies like smart text alignment etc.). This requires some Java knowledge to program, but in this case you can simply download the ColoredFieldCellRenderer.zip file and use it, even if you don’t know Java. The source code is included in the zip file, for anyone who is interested.

After using javaaddpath to add the zip file to the dynamic Java classpath (you can add it to the static classpath.txt file instead), the contained Java class file is available for use in Matlab. We configure it according to our data and then assign it to all our table’s columns.

Java savvy readers might complain that the data-processing should perhaps be done in the renderer class rather than in Matlab. I have kept it in Matlab because this would enable very easy modification of the highlighting algorithm, without any need to modify the generic Java renderer class.

Unfortunately, in the new uitable design (the version available since R2008a), JIDE and Matlab have apparently broken the standard MVC approach by using a table model that not only controls the data but also sets the table’s appearance (row-striping background colors, for example), and disregards column cell-renderers. In order for our custom cell renderer to have any effect, we must therefore replace Matlab’s standard DefaultUIStyleTableModel with a simple DefaultTableModel. This in itself is not enough – we also need to ensure that the uitable has an empty ColumnFormat property, because if it is non-empty then it overrides our cell-renderer.

In the following code, note that Java row and column indices start at 0, not at 1 like in Matlab. We need to be careful about indices when programming java in Matlab.

The rest of the code should be pretty much self explanatory (again – more details can be found in the above-mentioned report):

% Initialize our custom cell renderer class object
javaaddpath('ColoredFieldCellRenderer.zip');
cr = ColoredFieldCellRenderer(java.awt.Color.white);
cr.setDisabled(true);  % to bg-color the entire column
 
% Set specific cell colors (background and/or foreground)
for rowIdx = 1 : size(data,1)
 
  % Red/greed foreground color for the numeric data
  for colIdx = 2 : 8
    if data(rowIdx,colIdx) < 0
      cr.setCellFgColor(rowIdx-1,colIdx-1,java.awt.Color(1,0,0));    % red
    elseif data(rowIdx,colIdx) > 0
      cr.setCellFgColor(rowIdx-1,colIdx-1,java.awt.Color(0,0.5,0));  % green
    end
  end
 
  % Yellow background for significant rows based on p-value
  if data(rowIdx,12) < = 5 && data(rowIdx,11)~=0
    for colIdx = 1 : length(headers)
      cr.setCellBgColor(rowIdx-1,colIdx-1,java.awt.Color(1,1,0));    % yellow
    end
  end
 
  % Bold blue foreground for significant payouts
  if abs(data(rowIdx,11)) >= 2
    cr.setCellFgColor(rowIdx-1,10,java.awt.Color(0,0,1));    % blue
 
    % Note: the following could easily be done in the renderer, just like the colors
    boldPayoutStr = ['' num2str(data(rowIdx,11),'%.2f') ''];
    %jTable.setValueAt(boldPayoutStr,rowIdx-1,10);  % this is no good: overridden when table model is replaced below...
    dataCells{rowIdx,11} = boldPayoutStr;
  end
end
 
% Replace Matlab's table model with something more renderer-friendly...
jTable.setModel(javax.swing.table.DefaultTableModel(dataCells,headers));
set(hTable,'ColumnFormat',[]);
 
% Finally assign the renderer object to all the table columns
for colIdx = 1 : length(headers)
  jTable.getColumnModel.getColumn(colIdx-1).setCellRenderer(cr);
end

Finally something lively!

This may not take a beauty contest prize, but you must admit that it now looks more useful than the original table at the top of this article.

Related posts:
Uitable customization report In last week’s report about uitable sorting, I offered a report that I have written which covers uitable customization in detail. Several people have asked for more details about the...
Uitable sorting Matlab's uitables can be sortable using simple undocumented features...
Uitab colors, icons and images Matlab's semi-documented tab panels can be customized using some undocumented hacks...
Changing Matlab’s Command Window colors Matlab's Command Window foreground and background colors can be modified programmatically, using some of Matlab's undocumented internal Java classes. Here's how....

Tri-state checkbox

Yair Altman — Wed, 19 Oct 2011 14:04:20 +0000

When presenting information visually in graphical user interfaces (GUIs), we often need to present and enable interaction with state data (such as On/Off). In most cases, we would naturally use a checkbox to present the information and enable interaction. But What can we do if the data has three possible states. For example, Yes/No/Maybe, or: Full/Empty/Partial, or: Up/Down/Undetermined ?
Until today, Matlab GUIs had to resort to using drop-down (aka combo-box or popup-menu) or radio-button controls to present such information. However, would it not be nicer if we could still use a checkbox? Outside Matlab, such a control is known as a tri-state checkbox and many modern GUI frameworks support it. Well, surprise surprise, so does Matlab (although you would never guess it from the documentation).
CheckBoxTree
Last year, I have already described a built-in Matlab tree control whose nodes have tri-state checkboxes:
a regular MJTree (left) and a CheckBoxTree (right)
Today I will show how we can use these checkboxes as independent GUI controls.
Modifying the standard Matlab checkbox uicontrol
In order to modify the standard Matlab checkbox uicontrol, we need to first get its underlying Java component reference. This is done using the findjobj utility. We then update its UI wrapper to be the same as the CheckBoxTree‘s checkbox control.
To programmatically set a mixed state we update the ‘selectionState’ client property to SelectionState.MIXED (SelectionState also has the SELECTED and NOT_SELECTED values).
Here is an end-to-end example:
hCB = uicontrol('Style','checkbox', ...); jCB = findjobj(hCB); jCB.setUI(com.mathworks.mwswing.checkboxtree.TriStateButtonUI(jCB.getUI)); % Update the checkbox state to MIXED newState = com.mathworks.mwswing.checkboxtree.SelectionState.MIXED; jCB.putClientProperty('selectionState', newState); jCB.repaint;
Matlab checkboxes displaying mixed states
Displaying as an independent Java control
Instead of retrofitting a standard Matlab uicontrol as described above, we can directly use the standard javax.swing.JCheckBox which does not normally support tri-state (it only has two states), displaying it in our GUI with the built-in javacomponent function:
% Display the checkbox (UNSELECTED state at first) jCB = javax.swing.JCheckBox('JCheckBox - mixed',0); javacomponent(jCB, [10,70,150,20], gcf); % Update the checkbox state to MIXED import com.mathworks.mwswing.checkboxtree.* jCB.setUI(TriStateButtonUI(jCB.getUI)); jCB.putClientProperty('selectionState', SelectionState.MIXED); jCB.repaint;
Note that instead of using javax.swing.JCheckBox, we could use the internal Matlab class com.mathworks.mwswing.MJCheckBox, which directly extends JCheckBox and adds mnemonic (shortcut-key) support, but is otherwise fully compatible with JCheckBox. Actually, it is MJCheckBox which is the underlying Java component of the standard Matlab checkbox uicontrol.
Alternative controls
Now that we have seen that Matlab includes built-in support (well, at least support in the technical sense, not the official customer-support sense), would you be surprised to learn that it includes similar support in other internal components as well?
The internal Matlab class com.mathworks.mwt.MWCheckbox directly supports a tri-state (yes/no/maybe) checkbox, without any need to update its UI, as follows:
% Display the checkbox (UNSELECTED state at first) jCB = com.mathworks.mwt.MWCheckbox('MWCheckbox - mixed',0); javacomponent(jCB, [10,70,150,20], gcf); % Update the checkbox state to MIXED jCB.setMixedState(true); % Retrieve the current state isMixedFlag = jCB.isMixedState(); % true/false
MJCheckBox vs. MWCheckbox
Note that the State property, which controls the standard selected/unselected state, is entirely independent from the MixedState property. Both State and MixedState are boolean properties, so to get the actual checkbox state we need to query both of these properties.
Another internal Matlab class that we can use is JIDE’s com.jidesoft.swing.TristateCheckBox (which is pre-bundled in Matlab and is fully documented here).
There are many other tri-state checkbox alternatives available online (for example, here, here and here). We can easily include them in our Matlab GUI with the javacomponent function. Using external components we can be more certain of the compatibility issues in past and future Matlab releases. On the other hand, internal Matlab classes do have the advantage of being inherently accessible on all platforms of the same Matlab release, whereas non-Matlab components must be included in our deployment package.
Do you use any tri-state controls, either Matlab or external, in your work? If so, please share your experience in a comment below.

Related posts:
Recovering previous editor state Recovering the previous state of the Matlab editor and its loaded documents is possible using a built-in backup config file. ...
Determining axes zoom state The information of whether or not an axes is zoomed or panned can easily be inferred from an internal undocumented object....
JIDE Property Grids The JIDE components pre-bundled in Matlab enable creating user-customized property grid tables...
FindJObj GUI – display container hierarchy The FindJObj utility can be used to present a GUI that displays a Matlab container's internal Java components, properties and callbacks....

Customizing uicontrol border

Yair Altman — Sun, 31 Oct 2010 19:05:17 +0000

Today, a CSSM user posted the question how to modify the border of Matlab editboxes. There is of course no documented way to do this in plain Matlab. However, this is so easy to do using the edit-box’s undocumented underlying Java, that I decided to skip my regular weekly article schedule and post an out-of-band explanation.
As the CSSM poster correctly figured out, we first need to get the uicontrol’s underlying Java reference. This is done using my FindJObj utility. The next step is to get the Java object’s Border property:
>> hEdit = uicontrol('Style','Edit'); % create Matlab uicontrol >> jEdit = findjobj(hEdit) % get underlying Java reference jEdit = javahandle_withcallbacks.com.mathworks.hg.peer.EditTextPeer$hgTextField >> jEdit.Border % check the control's border ans = com.sun.java.swing.plaf.windows.XPStyle$XPFillBorder@e5a137 >> jEdit.Border.get BorderOpaque = on Class = [ (1 by 1) java.lang.Class array] LineColor = [0.498039 0.615686 0.72549] RoundedCorners = off Thickness = [1] ...
Unfortunately, as the CSSM poster has discovered, this Border property cannot be modified. Such an object is called immutable in Java; another common example is the Font property.
However, we can easily replace the object’s Border with a custom-made border, as follows:
lineColor = java.awt.Color(1,0,0); % =red thickness = 3; % pixels roundedCorners = true; newBorder = javax.swing.border.LineBorder(lineColor,thickness,roundedCorners); jEdit.Border = newBorder; jEdit.repaint; % redraw the modified control
editbox with regular border

editbox with custom border
Much more complex and interesting borders can be created in much the same way. Interested readers are referred to the official documentation of Java Borders or any decent Swing textbook.
We can use the same technique to remove the uicontrol’s borders altogether:
jEdit.Border = [];
editbox with no border
Setting the border as shown above works in much the same manner for all Java uicontrols. Simply use findjobj to get the Java reference and then update its Border property.
This article has described the Border property. Matlab uicontrols’ underlying Java objects contain numerous other useful properties and methods that can greatly extend our Matlab GUI, and I intend to describe some of them in the upcoming months/years.
Do you have any particular uicontrol customization that you would like me to describe? If so, please do post a comment.

Related posts:
Setting line position in an edit-box uicontrol Matlab uicontrols have many useful features that are only available via Java. Here's how to access them....
Additional uicontrol tooltip hacks Matlab's uicontrol tooltips have several limitations that can be overcome using the control's underlying Java object....
Uicontrol callbacks This post details undocumented callbacks exposed by the underlying Java object of Matlab uicontrols, that can be used to modify the control's behavior in a multitude of different events...
Customizing Matlab labels Matlab's text uicontrol is not very customizable, and does not support HTML or Tex formatting. This article shows how to display HTML labels in Matlab and some undocumented customizations...

JIDE Property Grids

Yair Altman — Thu, 22 Apr 2010 00:37:52 +0000

I would like to welcome guest blogger Levente Hunyadi.
Matlab’s property inspector
We often wish to edit properties of heterogeneous objects using a common interface. Matlab’s property inspector, invoked with the built-in inspect function, answers this need. The inspector is based on a two-column table of property names and values. Properties and their values are populated automatically, and the user can edit values in-place. The inspector enables property categorization, sub-categorization and sorting, which help users find and modify properties easily. For each property, the inspector displays a matching edit control: editbox/combobox/checkbox etc. This simplifies property value editing and prevents illegal value entry. Matlab’s GUI builder, GUIDE, uses the inspector to let users edit GUI properties such as position, color etc. It is also used by other tools such as the Plot Editor.
Matlab's built-in property inspector
The Matlab inspector can be embedded, with not-too-much effort, within Matlab GUI applications. Examples of this can be found in the FindJObj and UIInspect utilities.
FindJObj - embedded property inspector
Unfortunately, Matlab’s property inspector is limited to Handle Graphics, Java and COM objects, and cannot be used for structures or user-defined Matlab classes. We shall see below how to set up our own property grid, populate it with data, and subscribe to property change events. This is a rather procedural approach. It is usually more convenient to use a declarative approach in which a structure or Matlab class is passed to a function that automatically discovers its properties and their meta-information. The Property Grid utility at Matlab File Exchange provides these services.
A simple property grid
Matlab’s property inspector is based on a property grid control by JIDE Software. JIDE Grids is a collection of components that extend the standard Java Swing JTable component, and is included in each Matlab installation (/java/jarext/jide/jide-grids.jar under the Matlab root). In particular, JIDE Grids includes the PropertyTable class, which is a fully customizable property grid component. You can find further details on JIDE Grids in the Developer Guide and the Javadoc documentation.
There are several related classes associated with the PropertyTable class. First, a PropertyTableModel encapsulates all properties that are visualized in the property grid. Each property derives from the Property abstract class, which features some common actions to properties, most notably to get and set property value. DefaultProperty is a default concrete subclass of Property. Finally, PropertyPane decorates a property grid with icons for changing category view to alphabetically sorted view as well as expanding and collapsing categories, and a description text box at the bottom that can be shown or hidden.
Here are the DefaultProperty fields and their respective roles:
Field Role
Name Interal property name, not necessarily displayed, used as a key to identify the property.
DisplayName A short property name shown in the left column of the property grid.
Description A concise description of the property, shown at the bottom of the property pane, below the grid.
Type The Java type associated with the property, used to invoke the appropriate renderer or editor.
EditorContext An editor context object. If set, both the type and the context are used to look up the renderer or editor to use. This lets, for instance, one flag value to display as a true/false label, while another as a checkbox.
Category A string specifying the property’s category, for grouping purposes.
Editable Specifies whether the property value is modifiable or read-only.
Value The current property value, as a Java object.
Just as with any Java object, these fields may either be accessed with the Java get/set semantics (e.g. getName() or setName(name)), or the Matlab get/set semantics (e.g. get(prop,’Name’) or set(prop,’Name’,name)). When using the Matlab syntax, remember to wrap the Java object in a handle() call, to prevent a memory leak.
To use a property grid in Matlab, first construct a set of DefaultProperty objects. For each object, set at least the name, type and initial value. Next, add the properties to a table model. Finally, construct a property grid with the given table model and encapsulate in a property pane:
% Initialize JIDE's usage within Matlab com.mathworks.mwswing.MJUtilities.initJIDE; % Prepare the properties list list = java.util.ArrayList(); prop1 = com.jidesoft.grid.DefaultProperty(); prop1.setName('stringProp'); prop1.setType(javaclass('char',1)); prop1.setValue('initial value'); prop1.setCategory('My Category'); prop1.setDisplayName('Editable string property'); prop1.setDescription('A concise description for my property.'); prop1.setEditable(true); list.add(prop1); prop2 = com.jidesoft.grid.DefaultProperty(); prop2.setName('flagProp'); prop2.setType(javaclass('logical')); prop2.setValue(true); prop2.setCategory('My Category'); prop2.setDisplayName('Read-only flag property'); prop2.setEditable(false); list.add(prop2); % Prepare a properties table containing the list model = com.jidesoft.grid.PropertyTableModel(list); model.expandAll(); grid = com.jidesoft.grid.PropertyTable(model); pane = com.jidesoft.grid.PropertyPane(grid); % Display the properties pane onscreen hFig = figure; panel = uipanel(hFig); javacomponent(pane, [0 0 200 200], panel); % Wait for figure window to close & display the prop value uiwait(hFig); disp(prop1.getValue());
Here, com.mathworks.mwswing.MJUtilities.initJIDE is called to initialize JIDE’s usage within Matlab. Without this call, we may see a JIDE warning message in some Matlab releases. We only need to initJIDE once per Matlab session, although there is no harm in repeated calls.
javaclass is a function (included in the Property Grid utility, or directly downloadable from here) that returns a Java class for the corresponding Matlab type with the given dimension: javaclass(‘logical’) or javaclass(‘logical’,0) (a single logical flag value) returns a java.lang.Boolean class; javaclass(‘char’,1) (a character array) returns a java.lang.String class; javaclass(‘double’,2) (a matrix of double-precision floating point values) returns double[][].
javacomponent is the undocumented built-in Matlab function that adds Java Swing components to a Matlab figure, using the given dimensions and parent handle. When the user closes the figure, prop.getValue() fetches and displays the new property value.
A simple user-defined property grid
Next week’s article will show how to add more complex renderers and editors (display the flag value as a checkbox for example), define nested properties, and subscribe to property value change events. So stay tuned…

Related posts:
Advanced JIDE Property Grids JIDE property grids can use complex cell renderer and editor components and can signal property change events asynchronously to Matlab callbacks...
Plot LineSmoothing property LineSmoothing is a hidden and undocumented plot line property that creates anti-aliased (smooth unpixelized) lines in Matlab plots...
Axes LooseInset property Matlab plot axes have an undocumented LooseInset property that sets empty margins around the axes, and can be set to provide a tighter fit of the axes to their surroundings....
Tri-state checkbox Matlab checkboxes can easily be made to support tri-state functionality....

Additional uicontrol tooltip hacks

Yair Altman — Wed, 17 Feb 2010 17:25:52 +0000

Once again I’d like to welcome guest blogger Matthew Whitaker. Today Matt will discuss uicontrol tooltips hacks as the first of several posts that follow a logical thread culminating in the long promised article on the EDT.

A while back Yair wrote a cool article, Spicing up Matlab uicontrol tooltips, describing use of HTML formatting and images in uicontrol tooltips. I want to share some limitations I’ve seen with tooltips and their solution using the Matlab control’s underlying Java object.
Situation 1: Displaying a tooltip on disabled controls
One issue with the stock Matlab uicontrol tooltips is that if you turn the uicontrol’s Enable property to ‘inactive’ or ‘off’, its tooltip no longer displays. This is the behavior that we normally want, but occasionally we wish to display a tooltip on a disabled control, for example, to explain why the control is disabled.
You can use the findjobj utility to find the Java handle for the uicontrol. This handle can then be used to set the tooltip text. The tooltip will display if you disable the control using its Java handle’s Enabled property rather than the Matlab handle’s Enable property:
hButton = uicontrol('String','Button'); drawnow; jButton= findjobj(hButton); set(jButton,'Enabled',false); set(jButton,'ToolTipText','This is disabled for a reason');
As customary for Java objects, its properties can also be set using their corresponding accessor methods:
javaMethodEDT('setEnabled',jButton,false); javaMethodEDT('setToolTipText',jButton,'Button is disabled for a reason');
tooltip on a disabled uicontrol
Unfortunately, this hack does not work for ‘inactive’ controls. There is no direct Java analogy for inactive controls – it’s a Matlab extension. It appears that Matlab somehow intercepts the mouse events associated with inactive controls. My next post will show how event callback can be used to display tooltips for inactive controls.
As an alternative for inactive edit-box controls, we can simulate the inactive behavior by setting the Java object’s Editable property (or by using its setEditable() accessor method), then setting the tooltip. Note that the extremely-useful Java Editable property is unavailable in the Matlab handle, for some inexplicable reason:
hEditbox = uicontrol('String','Edit Text','Style','edit'); drawnow; jEditbox = findjobj(hEditbox); set(jEditbox,'Editable',false); set(jEditbox,'ToolTipText','Text is inactive for a reason');
tooltip on a non-editable editbox
Situation 2: Displaying a tooltip on truncated text
If we want to conditionally display a tooltip for an editbox uicontrol when the text exceeds the control’s width, we can use the TipWhenTruncatedEnabled property (or its corresponding setTipWhenTruncatedEnabled() method). This will display a tooltip with the editbox contents if the string is shown truncated. This saves the user having to scroll through the control to see its contents. I often use this for edit controls that may contain long path names:
hEditbox(1) = uicontrol('Style','edit','Units','norm','Pos',[0.1,0.8,0.4,0.05], 'String','Too Short'); hEditbox(2) = uicontrol('Style','edit','Units','norm','Pos',[0.1,0.7,0.2,0.05], 'String','Long Enough to Display a Tool Tip'); drawnow; jEditbox1 = findjobj(hEditbox(1)); jEditbox2 = findjobj(hEditbox(2)); set(jEditbox1,'TipWhenTruncatedEnabled',true); % property-based alternative javaMethod('setTipWhenTruncatedEnabled',jEditbox2,true); % method-based alternative
TipWhenTruncatedEnabled tooltip
The TipWhenTruncatedEnabled property property is also available for multi-line editboxes, but has (obviously) no effect when scrollbars are present. Also note that setting the TipWhenTruncatedEnabled property to true overrides any previous tooltip that might have been set for the editbox.
Finally, note that the TipWhenTruncatedEnabled property can also be set for the editbox component of popup-menu (aka drop-down) controls, after they have been set to be editable using their Java Editable property (note that both properties are false by default for Matlab uicontrols). In the following screenshot, the drop-down’s editbox component contained an HTML snippet, that is shown unformatted within the edit-box and HTML-formatted in the de-truncated tooltip:
de-truncated HTML-format tooltip
Situation 3: Controlling tooltip timing
As you have probably noticed, there is a slight delay between the time your mouse enters the control and when the tooltip actually appears. If you display a tooltip over a control for sufficiently long the tooltip will then disappear. Sometimes the default delays are too slow or fast for your application. These times can be controlled through the javax.swing.ToolTipManager. The ToolTipManager sets these parameters globally (including for your Matlab desktop components), but they are not persistent between sessions.
Some examples using the ToolTipManager:
btn = uicontrol('String','Button','Tooltip','This is a button.','Pos',[100,100,75,25]); txt = uicontrol('Style','edit','String','Edit Text','Tooltip','This is editable text','Pos',[100,50,75,25]); tm = javax.swing.ToolTipManager.sharedInstance; %static method to get ToolTipManager object initialDelay = javaMethodEDT('getInitialDelay',tm); %get the delay before display in milliseconds (=750 on my system) javaMethodEDT('setInitialDelay',tm,0); %set tooltips to appear immediately dismissDelay = javaMethodEDT('getDismissDelay',tm); %get the delay before the tooltip disappears (=10000 (10 sec) on my system) javaMethodEDT('setDismissDelay',tm,2000); %set the dismiss delay to 2 seconds javaMethodEDT('setEnabled',tm,false); %turns off all tooltips in system (including the Matlab desktop) javaMethodEDT('setEnabled',tm,true); javaMethodEDT('setInitialDelay',tm,initialDelay); javaMethodEDT('setDismissDelay',tm,dismissDelay);
Note that I have made extensive use of the undocumented built-in javaMethodEDT function to execute Java methods that affect Swing components on the Swing Event Dispatch Thread (EDT). I plan to write about EDT following my next post on event callback chaining.

Related posts:
Setting line position in an edit-box uicontrol Matlab uicontrols have many useful features that are only available via Java. Here's how to access them....
Customizing uicontrol border Matlab uicontrol borders can easily be modified - this article shows how...
Uicontrol callbacks This post details undocumented callbacks exposed by the underlying Java object of Matlab uicontrols, that can be used to modify the control's behavior in a multitude of different events...
Spicing up Matlab uicontrol tooltips Matlab uicontrol tooltips can be spiced-up using HTML and CSS, including fonts, colors, tables and images...

Continuous slider callback

Yair Altman — Mon, 08 Feb 2010 09:13:39 +0000

Every few months, a CSSM forum reader asks how to set up a continuously-invoked slider callback: Matlab’s slider uicontrol invokes the user callback only when the mouse button is released, and not continuously while the slider’s thumb is dragged. This functionality was again referred-to yesterday, and I decided it merits a dedicated post.
There are three distinct simple ways to achieve continuous callbacks:
Using Java callbacks
As explained in an earlier article, Matlab uicontrols are basically Java Swing objects that possess a large number of useful callbacks. Matlab sliders’ underlying Java objects, which are really not JSliders but JScrollBars, have an AdjustmentValueChangedCallback property that is useful for our purposes and is accessible using the FindJObj utility. Simply download FindJObj from the File Exchange, and then:
hSlider = uicontrol('style','slider', ...); jScrollBar = findjobj(hSlider); jScrollBar.AdjustmentValueChangedCallback = @myCbFcn; % or: set(jScrollBar,'AdjustmentValueChangedCallback',@myCbFcn)
Where myCbFcn is the Matlab callback function that will be invoked continuously when the arrow buttons are depressed or the slider’s thumb is dragged.
Using an event listener
An alternative to the Java route is to use Matlab’s undocumented handle.listener function to listen to the slider’s Action event, as follows:
hListener = handle.listener(hSlider,'ActionEvent',@myCbFcn);
This alternative is used by Matlab’s own imscrollpanel function:
if isJavaFigure % Must use these ActionEvents to get continuous events fired as slider % thumb is dragged. Regular callbacks on sliders give only one event % when the thumb is released. hSliderHorListener = handle.listener(hSliderHor,... 'ActionEvent',@scrollHorizontal); hSliderVerListener = handle.listener(hSliderVer,... 'ActionEvent',@scrollVertical); setappdata(hScrollpanel,'sliderListeners',... [hSliderHorListener hSliderVerListener]); else % Unfortunately, the event route is only available with Java Figures, % so platforms without Java Figure support get discrete events only % when the mouse is released from dragging the slider thumb. set(hSliderHor,'callback',@scrollHorizontal) set(hSliderVer,'callback',@scrollVertical) end
Using a property listener
The handle.listener function can also be used to listen to property value changes. In our case, set a post-set listener, that gets triggered immediately following Value property updates, as follows:
hhSlider = handle(hSlider); hProp = findprop(hhSlider,'Value'); % a schema.prop object hListener = handle.listener(hhSlider,hProp,'PropertyPostSet',@myCbFcn);
In addition to ‘PropertyPostSet’, we could also listen on ‘PropertyPreSet’, which is triggered immediately before the property is modified. There are also corresponding ‘*Get’ options. In relatively old Matlab releases (I believe R2007b and earlier, but I’m not certain), the option names were simply ‘PostSet’, ‘PreSet’ etc., without the ‘Property’ prefix.
Do you know of any other way to achieve continuous callbacks? If so, I would be delighted to hear in the comments section below.

Related posts:
Controlling callback re-entrancy Callback reentrancy is a major problem for frequently-fired events. Luckily, it can easily be solved....
Inactive Control Tooltips & Event Chaining Inactive Matlab uicontrols cannot normally display their tooltips. This article shows how to do this with a combination of undocumented Matlab and Java hacks....
Setting listbox mouse actions Matlab listbox uicontrol can be modified to detect mouse events for right-click context menus, dynamic tooltips etc....
Uicontrol callbacks This post details undocumented callbacks exposed by the underlying Java object of Matlab uicontrols, that can be used to modify the control's behavior in a multitude of different events...

Customizing listbox & editbox scrollbars

Yair Altman — Mon, 01 Feb 2010 17:40:03 +0000

A few days ago, a CSSM forum reader asked how to modify Matlab’s listbox scrollbars. Another user asked how to configure line-wrapping. I thought this is a good opportunity to describe how listbox and editbox scrollbars can be customized. The timing is particularly opportune, after I have recently described how the Matlab Editbox can be customized by accessing its underlying Java object using the FindJObj utility.
Both the listbox and the multi-line editbox uicontrols share a similar design: a multi-line Java control embedded within a JViewport within a JScrollPane (note that for historical reasons, the Java view-port class is called JViewport rather than the more standard camel-cased JViewPort). In addition to the view-port, the containing scroll-pane also contains two scrollbars (horizontal and vertical), as expected from standard Java scroll-panes.
JScrollPane components
Scrollbar policies
Control of the scroll-pane’s scrollbar behavior is done via the JScrollPane’s VerticalScrollBarPolicy and HorizontalScrollBarPolicy properties.
VerticalScrollBarPolicy accepts the self-explanatory values of:
VERTICAL_SCROLLBAR_ALWAYS (=22)
VERTICAL_SCROLLBAR_NEVER (=21)
and VERTICAL_SCROLLBAR_AS_NEEDED (=20)
HorizontalScrollBarPolicy accepts:
HORIZONTAL_SCROLLBAR_ALWAYS (=32)
HORIZONTAL_SCROLLBAR_NEVER (=31)
and HORIZONTAL_SCROLLBAR_AS_NEEDED (=30)
All these properties are static enumerated constants that can be referred using either their Java notation (e.g., JScrollPane.VERTICAL_SCROLLBAR_ALWAYS) or their equivalent numeric values. Using the non-numeric format is better, since it is more readable and the numeric values may change, but the choice is yours.
By default, Matlab implements a VerticalScrollBarPolicy of VERTICAL_SCROLLBAR_ALWAYS for sufficiently tall uicontrols (>20-25 pixels, which practically means always) and VERTICAL_SCROLLBAR_NEVER for shorter uicontrols.
For the horizontal scrollbar, Matlab implements a HorizontalScrollBarPolicy of HORIZONTAL_SCROLLBAR_NEVER for all editboxes and for narrow listboxes (<35 pixels), and HORIZONTAL_SCROLLBAR_AS_NEEDED for wide listboxes.
These settings are generally satisfactory. However, in some cases users may wish to modify the settings. For example, the default VerticalScrollBarPolicy setting of VERTICAL_SCROLLBAR_ALWAYS causes the vertical scrollbar to appear even when unneeded (the entire editbox content is visible). Also, we may wish to have a horizontal scrollbar on narrow listboxes and editboxes, something that the standard HORIZONTAL_SCROLLBAR_NEVER prevents. In both cases, a *_SCROLLBAR_AS_NEEDED policy might be more appropriate.
To modify these settings, we simply need to get the uicontrol’s underlying Java reference handle (using the FindJObj utility), and modify the appropriate property. For example:
% Create a multi-line (Max>1) editbox uicontrol hEditbox = uicontrol('style','edit', 'max',5, ...); % Get the Java scroll-pane container reference jScrollPane = findjobj(hEditbox); % Modify the scroll-pane's scrollbar policies % (note the equivalent alternative methods used below) set(jScrollPane,'VerticalScrollBarPolicy',20); % or: jScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED jScrollPane.setHorizontalScrollBarPolicy(30); % or: jScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED
default scrollbars (VERTICAL_SCROLLBAR_ALWAYS)

non-default scrollbars (VERTICAL_SCROLLBAR_AS_NEEDED)
Note that updating the uicontrol handle (hEditbox)’s Position property has the side-effect of automatically reverting the scrollbar policies to their default values (HORIZONTAL_SCROLLBAR_NEVER and VERTICAL_SCROLLBAR_ALWAYS/NEVER). This also happens whenever the uicontrol is resized interactively (by resizing its container figure window, for example). It is therefore advisable to set jScrollPane’s ComponentResizedCallback property to “unrevert” the policies:
cbStr = sprintf('set(gcbo,''VerticalScrollBarPolicy'',%d)', ... jScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED); hjScrollPane = handle(jScrollPane,'CallbackProperties'); set(hjScrollPane,'ComponentResizedCallback',cbStr);
Line-wrapping
By default, line-wrapping is turned on, effectively disabling horizontal scrolling (which is why Matlab set the HorizontalScrollBarPolicy to HORIZONTAL_SCROLLBAR_NEVER. However, in some cases it may be more useful to turn line-wrapping off and horizontal scrolling on using the TextArea’s setWrapping() method. Here’s a usage example:
jViewPort = jScrollPane.getViewport; jEditbox = jViewPort.getComponent(0); jEditbox.setWrapping(false); % do *NOT* use set(...)!!! newPolicy = jScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED; set(jScrollPane,'HorizontalScrollBarPolicy',newPolicy);
multi-line editbox with wrapping on
multi-line editbox with wrapping off
Notes:
setWrapping() only works for the default EditorKit, and fails for HTMLEditorKit – This is due to HTML’s inherent wrapping behavior, as can easily be seen in any browser webpage.
while setWrapping() may seem like a regular setter method for a Wrapping property, in reality it is not. Actually, set(jEditbox,’wrapping’,flag) may crash Matlab. So, always use the setWrapping(flag) method variant, which is entirely safe.

Related posts:
Rich Matlab editbox contents The Matlab editbox uicontrol does not handle HTML contents as do other uicontrols. In this article I show how this limitation can be removed....
Setting listbox mouse actions Matlab listbox uicontrol can be modified to detect mouse events for right-click context menus, dynamic tooltips etc....
Customizing uicontrol border Matlab uicontrol borders can easily be modified - this article shows how...
Customizing Matlab labels Matlab's text uicontrol is not very customizable, and does not support HTML or Tex formatting. This article shows how to display HTML labels in Matlab and some undocumented customizations...

Rich Matlab editbox contents

Yair Altman — Wed, 20 Jan 2010 21:04:11 +0000

In an earlier post, I mentioned that most Matlab uicontrols support HTML strings. Unfortunately, HTML is not supported in multi-line editbox contents. Today I will show how this limitation can be removed for a multi-line editbox, thereby enabling rich contents (enabling HTML for a single-line editbox needs a different solution).
We first need to get the editbox’s underlying Java object, as explained in my previous article about the findjobj utility. Since a multi-line editbox is contained within a scroll-pane, we need to dig within the scrollpane container to find the actual editable area object:
% Create a multi-line (Max>1) editbox uicontrol hEditbox = uicontrol('style','edit', 'max',5, ...); % Get the Java scroll-pane container reference jScrollPane = findjobj(hEditbox); % List the scroll-pane's contents: >> jScrollPane.list com.mathworks.hg.peer.utils.UIScrollPane[,0,0,100x50,...] javax.swing.JViewport[,1,1,81x48,...] com.mathworks.hg.peer.EditTextPeer$hgTextEditMultiline[,0,0,81x48,...,kit=javax.swing.text.StyledEditorKit@ce05fc,...] com.mathworks.hg.peer.utils.UIScrollPane$1[,82,1,17x48,...] com.sun.java.swing.plaf.windows.WindowsScrollBarUI$WindowsArrowButton[,0,31,17x17,...] com.sun.java.swing.plaf.windows.WindowsScrollBarUI$WindowsArrowButton[,0,0,17x17,...] com.mathworks.hg.peer.utils.UIScrollPane$2[,0,0,0x0,...] com.sun.java.swing.plaf.windows.WindowsScrollBarUI$WindowsArrowButton[,0,0,0x0,...] com.sun.java.swing.plaf.windows.WindowsScrollBarUI$WindowsArrowButton[,0,0,0x0,...]
In this listing, we see that jScrollPane contains a JViewport and two scrollbars (horizontal and vertical), as expected from standard Java scroll-panes. We need the internal hgTextEditMultiline object:
jViewPort = jScrollPane.getViewport; jEditbox = jViewPort.getComponent(0);
The retrieved jEditbox reference, is an object of class com.mathworks.hg.peer.EditTextPeer$hgTextEditMultiline, which indirectly extends the standard javax.swing.JTextPane. The default Matlab implementation of the editbox uicontrol simply enables a multi-line vertical-scrollable text area using the system font. However, the underlying JTextPane object enables many important customizations, including the ability to specify different font attributes (size/color/bold/italic etc.) and paragraph attributes (alignment etc.) for text segments (called style runs) and the ability to embed images, HTML and other controls.
Setting rich contents can be done in several alternative ways. From easiest to hardest:
Setting page URL
Use the setPage(url) method to load a text page from the specified URL (any pre-existing editbox content will be erased). The page contents may be plain text, HTML or RTF. The content type will automatically be determined and the relevant StyledEditorKit and StyledDocument will be chosen for that content. Additional StyledEditorKit content parsers can be registered to handle additional content types. Here’s an example loading an HTML page:
jEditbox.setPage('http://tinyurl.com/c27zpt');
where the URL’s contents are:
<html><body> <img src="images/dukeWaveRed.gif" width="64" height="64"> This is an uneditable <code>JEditorPane</code>, which was <em>initialized</em> with <strong>HTML</strong> text <font size=-2>from</font> a <font size=+2">URL</font>. <p>An editor pane uses specialized editor kits to read, write, display, and edit text of different formats. The Swing text package includes editor kits for plain text, HTML, and RTF. You can also develop custom editor kits for other formats. <script language="JavaScript" src="/js/omi/jsc/s_code_remote.js"></script> </body></html>
Matlab editbox initialized from an HTML webpage URL
Setting the EditorKit and ContentType
Set the requested StyledEditorKit (via setEditorKit()) or ContentType properties and then use setText() to set the text, which should be of the appropriate content type. Note that setting EditorKit or ContentType clears any existing text and left-aligns the contents (hgTextEditMultiline is center aligned by default). Also note that HTML
s get their own separate lines and that and opening and closing tags are accepted but unnecessary. For example:
jEditbox.setEditorKit(javax.swing.text.html.HTMLEditorKit); % alternative: jEditbox.setContentType('text/html'); htmlStr = [''... 'Matlab
GUI is ' ... 'highly customizable']; jEditbox.setText(htmlStr)
HTML contents in a Matlab editbox
Let’s show another usage example, of an event log file, spiced with icons and colored text based on event severity. First, define the logging utility function (the icon filenames may need to be changed based on your Matlab release):
function logMessage(jEditbox,text,severity) % Ensure we have an HTML-ready editbox HTMLclassname = 'javax.swing.text.html.HTMLEditorKit'; if ~isa(jEditbox.getEditorKit,HTMLclassname) jEditbox.setContentType('text/html'); end % Parse the severity and prepare the HTML message segment if nargin<3, severity='info'; end switch lower(severity(1)) case 'i', icon = 'greenarrowicon.gif'; color='gray'; case 'w', icon = 'demoicon.gif'; color='black'; otherwise, icon = 'warning.gif'; color='red'; end icon = fullfile(matlabroot,'toolbox/matlab/icons',icon); iconTxt =[',icon,'" height=16 width=16>']; msgTxt = [' ',text,'']; newText = [iconTxt,msgTxt]; endPosition = jEditbox.getDocument.getLength; if endPosition>0, newText=['
' newText]; end % Place the HTML message segment at the bottom of the editbox currentHTML = char(jEditbox.getText); jEditbox.setText(strrep(currentHTML,'',newText)); endPosition = jEditbox.getDocument.getLength; jEditbox.setCaretPosition(endPosition); % end of content end
Now, let’s use this logging utility function to log some messages:
logMessage(jEditbox, 'a regular info message...'); logMessage(jEditbox, 'a warning message...', 'warn'); logMessage(jEditbox, 'an error message!!!', 'error'); logMessage(jEditbox, 'a regular message again...', 'info');
Rich editbox contents (a log file)
HTML editboxes are normally editable, images included. In actual applications, we may wish to prevent editing the display log. To do this, simply call jEditbox.setEditable(false).
Setting a hyperlink handler is easy: first we need to ensure that we’re using an HTML content-type document. Next, set the editbox to be uneditable (hyperlinks display correctly when the editbox is editable, but are unclickable), using jEditbox.setEditable(false). Finally, set the callback function in the editbox’s HyperlinkUpdateCallback property:
jEditbox.setContentType('text/html'); jEditbox.setText('link: UndocumentedMatlab.com'); jEditbox.setEditable(false); hjEditbox = handle(jEditbox,'CallbackProperties'); set(hjEditbox,'HyperlinkUpdateCallback',@linkCallbackFcn); function linkCallbackFcn(src,eventData) url = eventData.getURL; % a java.net.URL object description = eventData.getDescription; % URL string jEditbox = eventData.getSource; switch char(eventData.getEventType) case char(eventData.getEventType.ENTERED) disp('link hover enter'); case char(eventData.getEventType.EXITED) disp('link hover exit'); case char(eventData.getEventType.ACTIVATED) jEditbox.setPage(url); end end
Hyperlink in editbox
Setting the style runs programmatically
Setting the styles programmatically, one style run after another, can be done via the text-pane’s Document property object. Individual character ranges can be set using the Document’s setCharacterAttributes method, or entire style runs can be inserted via insertString. Attributes are updated using the static methods available in javax.swing.text.StyleConstants. These methods include setting character attributes (font/size/bold/italic/strike-through/underline/subscript/superscript and foreground/background colors), paragraph attributes (indentation/spacing/tab-stops/bidi), image icons and any Swing Component (buttons etc.). Here is the end result:
Rich editbox contents: images, controls & font styles
Note that if a styled multi-line editbox is converted to a single-line editbox (by setting hEditbox’s Max property to 1), it loses all style information, embedded images and components. Returning to multi-line mode will therefore show only the plain-text.

Related posts:
Customizing listbox & editbox scrollbars Matlab listbox and multi-line editbox uicontrols have pre-configured scrollbars. This article shows how they can be customized....
Customizing help popup contents The built-in HelpPopup, available since Matlab R2007b, has a back-door that enables displaying arbitrary text, HTML and URL web-pages....
Setting line position in an edit-box uicontrol Matlab uicontrols have many useful features that are only available via Java. Here's how to access them....
Customizing Matlab labels Matlab's text uicontrol is not very customizable, and does not support HTML or Tex formatting. This article shows how to display HTML labels in Matlab and some undocumented customizations...

FindJObj GUI – display container hierarchy

Yair Altman — Tue, 12 Jan 2010 13:47:18 +0000

In my previous post, I explained how the findjobj utility can be used to access a Matlab component’s underlying Java component. Findjobj has another role: displaying the component hierarchy of complex Matlab containers such as the figure window, GUIDE or the Editor.
When findjobj is called with no output arguments, the function infers that the user requests to see the GUI version, rather than to get the control’s Java handle:
>> findjobj(gcf); % or: findjobj(gcf)
FindJObj GUI (click to zoom)
There are several note-worthy aspects in this graphical hierarchy presentation:
The hierarchy tree itself is displayed using the internal com.mathworks.hg.peer.UITreePeer Java object. This is the object that underlies the semi-documented uitree function. The hierarchy sub-components are presented as tree nodes, each having a separate icon based on the component type. In some cases (toolbar buttons for example), the component’s icon image is used for its corresponding tree node. A javax.swing.JProgressBar is presented while the tree is being populated, an action that can take a few seconds depending on the target figure’s complexity. Some tree branches which are normally uninteresting are automatically collapsed: hidden containers (these are also grayed-out), menubars, toolbars and scrollbars. In parallel to the Java container hierarchy, a separate tree branch is presented with the corresponding Matlab (Handle-Graphics, or HG) hierarchy.
Another GUI example - note the hidden (gray) items, the HG tree branch and the auto-collapsed MJToolBar container
Each node item gets a unique tooltip (see top screenshot above). Similarly, a unique context-menu (right-click menu) is attached to each node item with actions that are relevant for that node:
Item-specific context-menu
Finally, a node-selection callback is attached to the tree, that will flash a red border around the GUI control when its corresponding Java node-item is clicked/selected:
FindJObj - flashing red border around a toolbar icon
Once the tree was done, I set out to display and enable modifications of component properties and callbacks in separate adjacent panels. I used the internal com.mathworks.mlwidgets.inspector.PropertyView component to display the properties (this is the JIDE component that underlies the built-in inspect function). To prevent a JIDE run-time alert, I called com.mathworks.mwswing.MJUtilities.initJIDE. A label is added to the table’s header, displaying the currently selected sub-component’s class (e.g., “javax.swing.JButton”), and a tooltip with a color-coded list of all the control’s properties.
The callbacks table was implemented using com.jidesoft.grid.TreeTable to enable easy column resizing, but this is otherwise used as a simple data table. A checkbox was added to filter out the 30-odd standard Swing callbacks, which are non-unique to the selected sub-component (tree node). All the panels – tree, properties and callbacks – are then placed in resizable javax.swing.JSplitPanes and presented to the user.
I have omitted mention of some other undocumented features in findjobj. After all, space here is limited and the function is over 2500 lines long. I encourage you to download the utility and explore the code, and I gladly welcome your feedback.

Related posts:
FindJObj – find a Matlab component’s underlying Java object The FindJObj utility can be used to access and display the internal components of Matlab controls and containers. This article explains its uses and inner mechanism....
cprintf – display formatted color text in the Command Window cprintf is a utility that utilized undocumented Matlab desktop functionalities to display color and underline-styled formatted text in the Command Window...
uitree This article describes the undocumented Matlab uitree function, which displays data in a GUI tree component...
Tri-state checkbox Matlab checkboxes can easily be made to support tri-state functionality....

FindJObj – find a Matlab component’s underlying Java object

Yair Altman — Wed, 06 Jan 2010 21:06:33 +0000

In a previous post, I explained that all Matlab GUI (except the axes plotting engine) is based on Java components, and showed how we can use this information to display HTML contents in Matlab uicontrols. In other posts, I have shown how a utility called findjobj can be used to access the underlying Java components to enable customizations that are unavailable in standard Matlab: setting the line location in an edit-box, customizing button appearance, setting uicontrol callbacks, or setting list-box mouse actions. I have also shown how findjobj can be used to display the component hierarchy of complex Matlab containers such as the figure window, GUIDE or the Editor.
The time is therefore well overdue for a formal introduction of findjobj, explaining its uses and internal mechanism. Of course, readers are welcome to continue using findjobj as a black-box utility, but I think important insight can be gained from understanding its inner details. Findjobj‘s code is available for free download on the MathWorks File Exchange. It is one of my favorite submissions and is apparently well-liked by users, being highly reviewed and highly downloaded.
Findjobj has two main purposes:
Find the underlying Java object reference of a given Matlab handle – Historically this was the original purpose, hence the utility’s name. Findjobj was meant to extend Matlab’s standard findobj function, which does not expose Java components.
Display a container’s internal components hierarchy in a graphical user interface, to facilitate visualization of complex containers. This was later extended to also display and allow modification of the sub-components’ properties and callbacks.
Today I will focus on the first (programmatic) aspect; next week I will describe the second (GUI) aspect.
Findjobj‘s heart is finding a control’s underlying Java handle. Unfortunately, this is not exposed by Matlab except in very rare cases. As hard as I tried, I could not find a way to directly access the underlying Java-peer handle. I therefore resorted to getting the control’s enclosing Java frame (window) reference, and then working down its sub-components hierarchy until finding the Java object(s) which satisfy the position and/or class criteria. To get the enclosing Java frame (aka TopLevelAncestor), I use the Matlab figure’s undocumented JavaFrame property. Using this property issues a standard warning (since Matlab release R2008a) of becoming obsolete in some future Matlab release. Since it worked so far, I have turned off this warning in findjobj‘s code, but note that this code may well fail in some future Matlab version. If and when JavaFrame does become obsolete, be sure to look in this blog for workarounds…
Traversing the frame’s hierarchy presents several challenges: Main-menu items are accessed using different functions than other Swing components or sub-containers, and are not automatically accessible until first displayed. I have overcome this latter challenge by simulating a menu-open action in case menus should be searched (this is off by default since it takes several seconds and also changes the GUI focus). For “regular” sub-containers, sometimes we need to loop over getComponent(…) and in some other cases over getChildAt(…).
Another challenge was presented by the fact that Java positions start at (0,0) in the top left corner increasing rightward and downward, rather than starting at (1,1) in the bottom left and increasing upward as in Matlab. Moreover, Java positions are always pixel-based and relative to their parent container, which is different from Matlab (if the Matlab units is ‘pixels’ then the value is absolute; if ‘normalized’ then it returns a non-pixel value). To further complicate matters, some Matlab controls have a different size than their Java counterparts: some controls have a 5-pixel margins while others not, some controls are shifted by a pixel or two from their container’s border (for a total offset of up to 7 pixels), while some controls (such as popup-menus) have an entirely different reported size. In theory, we could use the Matlab component’s undocumented PixelBounds property (much faster than getpixelposition), but unfortunately PixelBounds turns out to be unreliable and returns erroneous values in many cases. Finally, different Java containers/components have different ways of returning their position: for some it is a getLocation() method, for others it is getX()/getY() and for others it is the X and Y properties (that sometimes have no corresponding getX()/getY() accessor methods!).
Having finally overcome all these challenges (and quite a few smaller ones, documented within the source code), I have wrapped the algorithm in a function interface that tries to emulate findobj‘s. Using findjobj can now be as easy as:
% Modify the mouse cursor when over the button hButton = uicontrol('string','click me!'); jButton = findjobj(hButton); jButton.setCursor(java.awt.Cursor(java.awt.Cursor.HAND_CURSOR))
Modified uicontrol cursor - a Java property
…or as complex as:
% Find all non-button controls with the specified label jControls = findjobj('property',{'text','click me!'}, 'not','class','button');
Space here is limited and findjobj is over 2500 lines long, so I have obviously not covered everything. I encourage you to download the utility and explore the code, and I gladly welcome your feedback.

Related posts:
FindJObj GUI – display container hierarchy The FindJObj utility can be used to present a GUI that displays a Matlab container's internal Java components, properties and callbacks....
Setting status-bar components Matlab status-bars are Java containers in which we can add GUI controls such as progress-bars, not just simple text labels...
Date selection components The JIDE package, pre-bundled in Matlab, contains several GUI controls for selecting dates - this article explains how they can be used...
Plot-type selection components Several built-in components enable programmatic plot-type selection in Matlab GUI - this article explains how...

Field	Role
Name	Interal property name, not necessarily displayed, used as a key to identify the property.
DisplayName	A short property name shown in the left column of the property grid.
Description	A concise description of the property, shown at the bottom of the property pane, below the grid.
Type	The Java type associated with the property, used to invoke the appropriate renderer or editor.
EditorContext	An editor context object. If set, both the type and the context are used to look up the renderer or editor to use. This lets, for instance, one flag value to display as a true/false label, while another as a checkbox.
Category	A string specifying the property’s category, for grouping purposes.
Editable	Specifies whether the property value is modifiable or read-only.
Value	The current property value, as a Java object.