Undocumented Matlab
  • SERVICES
    • Consulting
    • Development
    • Training
    • Gallery
    • Testimonials
  • PRODUCTS
    • IQML: IQFeed-Matlab connector
    • IB-Matlab: InteractiveBrokers-Matlab connector
    • EODML: EODHistoricalData-Matlab connector
    • Webinars
  • BOOKS
    • Secrets of MATLAB-Java Programming
    • Accelerating MATLAB Performance
    • MATLAB Succinctly
  • ARTICLES
  • ABOUT
    • Policies
  • CONTACT
  • SERVICES
    • Consulting
    • Development
    • Training
    • Gallery
    • Testimonials
  • PRODUCTS
    • IQML: IQFeed-Matlab connector
    • IB-Matlab: InteractiveBrokers-Matlab connector
    • EODML: EODHistoricalData-Matlab connector
    • Webinars
  • BOOKS
    • Secrets of MATLAB-Java Programming
    • Accelerating MATLAB Performance
    • MATLAB Succinctly
  • ARTICLES
  • ABOUT
    • Policies
  • CONTACT

Listbox selection hacks

July 13, 2016 4 Comments

Last week a reader on the CSSM newsgroup asked whether it is possible to programmatically deselect all listbox items. By default, Matlab listboxes enable a single item selection: trying to deselect it interactively has no effect, while trying to set the listbox’s Value property to empty ([]) results in the listbox disappearing and a warning issued to the Matlab console:
Single-selection Matlab listbox

>> hListbox = uicontrol('Style','list', 'String',{'item #1','item #2','item #3','item #4','item #5','item #6'});
>> set(hListbox,'Value',[]);
Warning: Single-selection 'listbox' control requires a scalar Value.
Control will not be rendered until all of its parameter values are valid
(Type "warning off MATLAB:hg:uicontrol:ValueMustBeScalar" to suppress this warning.)

The reader’s question was whether there is a way to bypass this limitation so that no listbox item will be selected. The answer to this question was provided by MathWorker Steve(n) Lord. Steve is a very long-time benefactor of the Matlab community with endless, tireless, and patient advise to queries small and large (way beyond the point that would have frustrated mere mortals). Steve pointed out that by default, Matlab listboxes only enable a single selection – not more and not less. However, when the listbox’s Max value is set to be >1, the listbox enables multiple-items selection, meaning that Value accepts and reports an array of item indices, and there is nothing that prevents this array from being empty (meaning no items selected):

>> hListbox = uicontrol('Style','list', 'Max',2, 'String',{'item #1','item #2','item #3','item #4','item #5','item #6'});
>> set(hListbox,'Value',[]);  % this is ok - listbox appears with no items selected

>> hListbox = uicontrol('Style','list', 'Max',2, 'String',{'item #1','item #2','item #3','item #4','item #5','item #6'}); >> set(hListbox,'Value',[]); % this is ok - listbox appears with no items selected

Note: actually, the listbox checks the value of Max–Min, but by default Min=0 and there is really no reason to modify this default value, just Max.
While this makes sense if you think about it, the existing documentation makes no mention of this fact:

The Max property value helps determine whether the user can select multiple items in the list box simultaneously. If Max – Min > 1, then the user can select multiple items simultaneously. Otherwise, the user cannot select multiple items simultaneously. If you set the Max and Min properties to allow multiple selections, then the Value property value can be a vector of indices.

Some readers might think that this feature is not really undocumented, since it does not directly conflict with the documentation text, but then so are many other undocumented aspects and features on this blog, which are not mentioned anywhere in the official documentation. I contend that if this feature is officially supported, then it deserves an explicit sentence in the official documentation.
However, the original CSSM reader wanted to preserve Matlab’s single-selection model while enabling deselection of an item. Basically, the reader wanted a selection model that enables 0 or 1 selections, but not 2 or more. This requires some tweaking using the listbox’s selection callback:

set(hListbox,'Callback',@myCallbackFunc);
...
function test(hListbox, eventData)
   value = get(hListbox, 'Value');
   if numel(value) > 1
       set(hListbox, 'Value', value(1));
   end
end

set(hListbox,'Callback',@myCallbackFunc); ... function test(hListbox, eventData) value = get(hListbox, 'Value'); if numel(value) > 1 set(hListbox, 'Value', value(1)); end end

…or a callback-function version that is a bit better because it takes the previous selection into account and tries to set the new selection to the latest-selected item (this works in most cases, but not with shift-clicks as explained below):

function myCallbackFunc(hListbox, eventData)
   lastValue = getappdata(hListbox, 'lastValue');
   value = get(hListbox, 'Value');
   if ~isequal(value, lastValue)
      value2 = setdiff(value, lastValue);
      if isempty(value2)
         setappdata(hListbox, 'lastValue', value);
      else
         value = value2(1);  % see quirk below
         setappdata(hListbox, 'lastValue', value);
         set(hListbox, 'Value', value);
      end
   end
end

function myCallbackFunc(hListbox, eventData) lastValue = getappdata(hListbox, 'lastValue'); value = get(hListbox, 'Value'); if ~isequal(value, lastValue) value2 = setdiff(value, lastValue); if isempty(value2) setappdata(hListbox, 'lastValue', value); else value = value2(1); % see quirk below setappdata(hListbox, 'lastValue', value); set(hListbox, 'Value', value); end end end

This does the job of enabling only a single selection at the same time as allowing the user to interactively deselect that item (by ctrl-clicking it).
There’s just a few quirks: If the user selects a block of items (using shift-click), then only the second-from-top item in the block is selected, rather than the expected last-selected item. This is due to line #9 in the callback code which selects the first value. Matlab does not provide us with information about which item was clicked, so this cannot be helped using pure Matlab. Another quirk that cannot easily be solved using pure Matlab is the flicker that occurs when the selection changes and is then corrected by the callback.
We can solve both of these problems using the listbox’s underlying Java component, which we can retrieve using my findjobj utility:

% No need for the standard Matlab callback now
set(hListbox,'Callback',[]);
% Get the underlying Java component peer
jScrollPane = findjobj(h);
jListbox = jScrollPane.getViewport.getView;
jListbox = handle(jListbox,'CallbackProperties');  % enable callbacks
% Attach our callback to the listbox's Java peer
jListbox.ValueChangedCallback = {@myCallbackFunc, hListbox};
...
function myCallbackFunc(jListbox, eventData, hListbox)
   if numel(jListbox.getSelectedIndices) > 1
      set(hListbox, 'Value', jListbox.getLeadSelectionIndex+1);  % +1 because Java indices start at 0
   end
end

% No need for the standard Matlab callback now set(hListbox,'Callback',[]); % Get the underlying Java component peer jScrollPane = findjobj(h); jListbox = jScrollPane.getViewport.getView; jListbox = handle(jListbox,'CallbackProperties'); % enable callbacks % Attach our callback to the listbox's Java peer jListbox.ValueChangedCallback = {@myCallbackFunc, hListbox}; ... function myCallbackFunc(jListbox, eventData, hListbox) if numel(jListbox.getSelectedIndices) > 1 set(hListbox, 'Value', jListbox.getLeadSelectionIndex+1); % +1 because Java indices start at 0 end end

We can use a similar mechanism to control other aspects of selection, for example to enable only up to 3 selections but no more etc.
We can use this underlying Java component peer for a few other useful selection-related hacks: First, we can use the peer’s RightSelectionEnabled property or setRightSelectionEnabled() method to enable the user to select by right-clicking listbox items (this is disabled by default):

jListbox.setRightSelectionEnabled(true);  % false by default
set(jListbox,'RightSelectionEnabled',true);  % equivalent alternative

jListbox.setRightSelectionEnabled(true); % false by default set(jListbox,'RightSelectionEnabled',true); % equivalent alternative

A similarly useful property is DragSelectionEnabled (or the corresponding setDragSelectionEnabled() method), which is true by default, and controls whether the selection is extended to other items when the mouse drags an item up or down the listbox.
Finally, we can control whether in multi-selection mode we enable the user to only select a single contiguous block of items, or not (which is Matlab’s default behavior). This is set via the SelectionMode property (or associated setSelectionMode() method), as follows:

jListbox.setSelectionMode(javax.swing.ListSelectionModel.SINGLE_INTERVAL_SELECTION);
jListbox.setSelectionMode(1);  % equivalent alternative (less maintainable/readable, but simpler)

jListbox.setSelectionMode(javax.swing.ListSelectionModel.SINGLE_INTERVAL_SELECTION); jListbox.setSelectionMode(1); % equivalent alternative (less maintainable/readable, but simpler)

SINGLE_SELECTION (default for Max=1) SINGLE_INTERVAL_SELECTION (only possible with Java) MULTIPLE_INTERVAL_SELECTION (default for Max>1)
SINGLE_SELECTION =0 SINGLE_INTERVAL_SELECTION =1 MULTIPLE_INTERVAL_SELECTION =2
(Matlab default for Max=1) (only possible with Java) (Matlab default for Max>1)


Additional listbox customizations can be found in related posts on this blog (see links below), or in section 6.6 of my Matlab-Java Programming Secrets book (which is still selling nicely almost five years after its publication, to the pleasant surprise of my publisher…).

Related posts:

  1. Customizing listbox/combobox items – Matlab listboxes can be customized using custom Java cell-renderers. ...
  2. Additional uicontrol tooltip hacks – Matlab's uicontrol tooltips have several limitations that can be overcome using the control's underlying Java object....
  3. Setting listbox mouse actions – Matlab listbox uicontrol can be modified to detect mouse events for right-click context menus, dynamic tooltips etc....
  4. Smart listbox & editbox scrollbars – Matlab listbox and multi-line editbox scrollbars can easily be made smarter, for improved appearance. ...
  5. Font selection components – Several built-in components enable programmatic font selection in Matlab GUI - this article explains how. ...
  6. Listbox layout customization – Matlab's listbox layout can be modified to display multiple item columns and different inter-cell margins. ...
Callbacks Java uicontrol Undocumented feature
Print Print
« Previous
Next »
4 Responses
  1. Radek July 15, 2016 at 00:27 Reply

    I am trying to figure out how to simulate held Ctrl key in ListBox.

    I already tried using the callback and programatically add previous selection to new one, but this one works when mouse key is released, so everything goes empty and then selected back.
    MousePressedCallback doesn’t work well either because selection is performed after this event so my selection is overridden anyway.

    I have a feeling something would need to be changed setSelectionModel

    • Yair Altman July 16, 2016 at 23:32 Reply

      @Radek – you are not making any sense. “Simulate held Ctrl key”? all you need to do is to set the Value property to an array of indexes (e.g. [1,3,5,7]) and then the listbox selection will be updated appropriately.

      • Radek July 18, 2016 at 20:10

        @Yair Altman – I meant I want to be able to click items on the list and each time a click new item it would be selected without clearing the others. So the user by default wouldn’t need to hold Ctrl key.
        I know in Java it is possible to override SelectionModel behavior, but in Matlab I don’t know how.

      • Yair Altman July 19, 2016 at 11:35

        @Radek – I think that the end-result would not be intuitive to users so I advise against doing this.

        If you still want to do it, then you could either update the underlying Java SelectionModel, or do it programmatically in Matlab: you could use a similar callback function as the second one in my post, and use the Matlab union function to merge the previous selection values with the newly-selected value(s).

Leave a Reply
HTML tags such as <b> or <i> are accepted.
Wrap code fragments inside <pre lang="matlab"> tags, like this:
<pre lang="matlab">
a = magic(3);
disp(sum(a))
</pre>
I reserve the right to edit/delete comments (read the site policies).
Not all comments will be answered. You can always email me (altmany at gmail) for private consulting.

Click here to cancel reply.

Useful links
  •  Email Yair Altman
  •  Subscribe to new posts (email)
  •  Subscribe to new posts (feed)
  •  Subscribe to new posts (reader)
  •  Subscribe to comments (feed)
 
Accelerating MATLAB Performance book
Recent Posts

Speeding-up builtin Matlab functions – part 3

Improving graphics interactivity

Interesting Matlab puzzle – analysis

Interesting Matlab puzzle

Undocumented plot marker types

Matlab toolstrip – part 9 (popup figures)

Matlab toolstrip – part 8 (galleries)

Matlab toolstrip – part 7 (selection controls)

Matlab toolstrip – part 6 (complex controls)

Matlab toolstrip – part 5 (icons)

Matlab toolstrip – part 4 (control customization)

Reverting axes controls in figure toolbar

Matlab toolstrip – part 3 (basic customization)

Matlab toolstrip – part 2 (ToolGroup App)

Matlab toolstrip – part 1

Categories
  • Desktop (45)
  • Figure window (59)
  • Guest bloggers (65)
  • GUI (165)
  • Handle graphics (84)
  • Hidden property (42)
  • Icons (15)
  • Java (174)
  • Listeners (22)
  • Memory (16)
  • Mex (13)
  • Presumed future risk (394)
    • High risk of breaking in future versions (100)
    • Low risk of breaking in future versions (160)
    • Medium risk of breaking in future versions (136)
  • Public presentation (6)
  • Semi-documented feature (10)
  • Semi-documented function (35)
  • Stock Matlab function (140)
  • Toolbox (10)
  • UI controls (52)
  • Uncategorized (13)
  • Undocumented feature (217)
  • Undocumented function (37)
Tags
ActiveX (6) AppDesigner (9) Callbacks (31) Compiler (10) Desktop (38) Donn Shull (10) Editor (8) Figure (19) FindJObj (27) GUI (141) GUIDE (8) Handle graphics (78) HG2 (34) Hidden property (51) HTML (26) Icons (9) Internal component (39) Java (178) JavaFrame (20) JIDE (19) JMI (8) Listener (17) Malcolm Lidierth (8) MCOS (11) Memory (13) Menubar (9) Mex (14) Optical illusion (11) Performance (78) Profiler (9) Pure Matlab (187) schema (7) schema.class (8) schema.prop (18) Semi-documented feature (6) Semi-documented function (33) Toolbar (14) Toolstrip (13) uicontrol (37) uifigure (8) UIInspect (12) uitools (20) Undocumented feature (187) Undocumented function (37) Undocumented property (20)
Recent Comments
  • Patrick Fitzgerald (1 day 22 hours ago): Just a heads up to anyone else digging around for help related to this: if you assign BackrgoundColor to a pushbutton-style uicontrol, it seems to prevent you from...
  • Vasiliy (17 days 18 hours ago): Hi Yair, i’m trying to use the MonthChooserPanel class. com.mathworks.mwswing.MJUtilit ies.initJIDE; handles.jPanel = com.jidesoft.combobox.MonthCho oserPanel;...
  • DM (17 days 18 hours ago): Hi Yair, I’m trying to use the MonthChooserPanel class. com.mathworks.mwswing.MJUtilit ies.initJIDE; handles.jPanel = com.jidesoft.combobox.MonthCho oserPanel; [handles.hPanel,...
  • Yair Altman (21 days 10 hours ago): @Alex – thanks, but keep in mind that new functions will only work on the recent Matlab releases. If your code needs to work on older Matlab releases, you could revert to...
  • Alex Churchill (21 days 11 hours ago): I was looking up how to do this exact task today. I was about to hold my nose and use the internal controllib function, when I happened to chance across a slightly newer...
  • Sebastian Hölz (27 days 17 hours ago): I have not investigated this in detail, but I think one way to go in new versions of Matlab (>2019b) might be to use listeners to suitable figure properties, e.g. fig =...
  • Prathep (27 days 20 hours ago): Hi Yair, Thanks for your introduction on Matlab Toostrip. Is there any way to add Matlab toolstrip for uifigures as you have done already for figure?
  • Josh (34 days 2 hours ago): Dear Yair, Small typo; you wrote >>Move lines up or down – CTRL + ALT + UP or DOWN allows you to move selected lines up or down but it’s actually ALT+SHIFT then UP/DOWN...
  • Yair Altman (40 days 21 hours ago): You can try to increase the Java heap memory size in the Matlab preferences (General => Java Heap Memory). Any changes to the settings will only take effect after restarting...
  • Thomas (40 days 22 hours ago): Hello, thanks for sharing! I currently receive the following memory error message when using savezip with a big object (Matlab R2020b, Windows 10). Error using...
  • Yair Altman (44 days 6 hours ago): Yerlan – either use menuItem1.setEnabled(0) or set(menuItem1,'Enabled',0)
  • Manzn (44 days 9 hours ago): Thank you man! you saved me, when there was no more light 😀
  • Yerlan (45 days 13 hours ago): Hello Mr. Altman, how can I disable menu items in the context menu? E.g. when I am trying to do this: menuItems = jmenu.getSubElements; menuItem1 = menuItems(1);...
  • Yair Altman (46 days 6 hours ago): Thanks for the note Eric – you forgot the crucial call to jTable.setLabelTable(labelTabl e) – I added it into your code snippet above.
  • Erik (47 days 17 hours ago): Thank you for this — I don’t know if this has been mentioned anywhere else before, but it could be useful to mention how to add custom labels to a jslider. I did the...
Contact us
Undocumented Matlab © 2009 - Yair Altman
Scroll to top