FindJObj GUI – display container hierarchy

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)

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

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

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

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:

  1. 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....
  2. 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...
  3. uitree This article describes the undocumented Matlab uitree function, which displays data in a GUI tree component...
  4. Tri-state checkbox Matlab checkboxes can easily be made to support tri-state functionality....
  5. Editbox data input validation Undocumented features of Matlab editbox uicontrols enable immediate user-input data validation...
  6. uiinspect uiinspect is a Matlab utility that displays detailed information about an object's methods, properties and callbacks in a single GUI window....

Categories: Figure window, GUI, Handle graphics, High risk of breaking in future versions, Java, UI controls, Undocumented feature

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3 Responses to FindJObj GUI – display container hierarchy

  1. Pingback: JIDE Property Grids | Undocumented Matlab

  2. Patrice Tscherrig says:


    I really love this tool. Perfect! One question – I really did not find it out myself. How do you manage the resize behavior of the tree pane? I.e. that you can move over the mouse on the tree pane and adjust it to make it less wide?

    Best Regards,

    • @Patrice – findjobj uses JSplitPanes, which enable easy resizing of the left/right or top/bottom panes. I simply placed the tree in the top left pane and the JSplitPane control took care of the rest. Easy.

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<pre lang="matlab">
a = magic(3);