Introduction

Using a pure-Java Swing-based Graphical User Interface (GUI) has several important advantages compared to using a pure-Matlab GUI:

• Java GUI widget toolkit provides a large collection of components (scrollbar, slider, etc…) and layouts (card, spring, etc…)
• Multiple event handling options
• Mature third-party Java Swing IDEs for quick and easy GUI development (Netbeans, Eclipse, etc…)
• Supports pluggable look and feel that allows applications to have a look and feel that is unrelated to the underlying platform.
• Java Swing’s window icon can be modified, whereas Mathworks apparently places an [entirely unreasonable] license restriction on modifying the Matlab figure window icon.

When Matlab is in development (non-deployed) mode, we can load and display a Java JFrame using the following Matlab code:

% Add Java library to dynamic Java classpath
javaaddpath([pwd '\ExampleWindow.jar']);
% Get example Java window from the library
jFrame = examplewindow.JavaWindow();
% Get Java buttons
% Note: see https://undocumentedmatlab.com/articles/matlab-callbacks-for-java-events-in-r2014a
plotMeshButton = handle(jFrame.getPlotMeshButton(),    'CallbackProperties');
showWarnButton = handle(jFrame.getShowWarnDlgButton(), 'CallbackProperties');
% Set Java button callbacks
set(plotMeshButton, 'ActionPerformedCallback', @myPlotMeshCallback);
set(showWarnButton, 'ActionPerformedCallback', @myShowWarnCallback);
% Display the Java window
jFrame.setVisible(true);

Java JFrame created in Matlab (click for full-size image)

The problem

All this works great when ran within the Matlab environment. However, when the Matlab source code file (.m) is compiled as a Windows standalone executable application, when running the resulting executable the Java window appears for a short period and then terminates (exits). Without a visible Matlab figure, the compiled Matlab application does not retain the Java window open. The JFrame flashes on for a split-second, and then vanishes.

The solution

To fix this problem, it turns out that we only need to add the Matlab waitfor command after making the Java window visible:

% (earlier code as above)
% Display the Java window
jFrame.setVisible(true);
if isdeployed
    waitfor(jFrame);
end

Java JFrame in deployed Matlab (click for full-size image)

The post Using pure Java GUI in deployed Matlab apps appeared first on Undocumented Matlab.

function updateInterface( lookandfeel )
    % Preserve the original L&F, before updating
    originalLnF = javax.swing.UIManager.getLookAndFeel;
    % Update the L&F in the demo figure as requested
    ... (all the existing code within the function)
    % Restore the original L&F for any new figure/window
    javax.swing.UIManager.setLookAndFeel(originalLnF);
end  % updateInterface

Note that after changing the L&Fs several times, some L&F properties night get “mixed-up” causing odd-looking L&Fs. The simplest solution in this case is to restart Matlab…

The post JTattoo look-and-feel demo appeared first on Undocumented Matlab.

% Create a Java button
jButton = javacomponent(javax.swing.JButton('click me'), [20,20,60,20], gcf);
% Assign a Matlab callback
hButton = handle(jButton, 'CallbackProperties');
set(hButton, 'ActionPerformedCallback', @myCallback);
% Matlab callback function
function myCallback(hObject, hEventData)
    % Insert your code here
end

This approach works fine for simple pure-Java GUI created using an IDE (for example, NetBeans or Eclipse) that only have a small number of controls. You can retrieve all the Java controls in Matlab and set the callbacks as shown in the above example.
Unfortunately, practical GUIs often contain numerous controls. Assigning each control a different Matlab callback can be quite tedious.

Using a callback switchyard function

A workaround to this problem can be achieved using an invisible/hidden static Java JButton. During Matlab initialization, assign a single callback for the static Java JButton:

% Return a reference to the GUI's static trigger button
triggerButton = statictrigger.triggerCls.getTrigger();
% Assign Matlab switchyard callback for triggerButton
buttonProps = handle(triggerButton, 'callbackproperties');
set(triggerButton, 'ActionPerformedCallback',@TriggerCallback);

When an event is triggered by any monitored control in the Java GUI, then within the Java code set the static button’s action command string to the desired Matlab callback name (a String) and invoke the static button’s doClick() method to trigger the Matlab TriggerCallback callback. Based on the action command string, this callback invokes the appropriate Matlab function. In this manner, Matlab’s TriggerCallback() acts as a switchyard function to the actual callback functions:

function TriggerCallback(hObject, hEventData)
   actionCmd = char( hObject.getActionCommand() );
   hgfeval(actionCmd, hObject, hEventData);
end

Note how the char function converts the Java action command (a java.lang.String object) into Matlab char array. The requested Matlab function is then dynamically invoked using Matlab’s semi-documented hgfeval function, which Yair will describe in another article later this month.
The next few sections will look into the sample application in more detail. This application can be downloaded from here.

Java GUI

Firstly, let’s look into the Java GUI:

private void showActionPerformed(java.awt.event.ActionEvent evt)
{
    // Add form values to hash map
    hMap.put(name.getName(), name.getText());
    hMap.put(age.getName(), age.getValue());
    hMap.put(sex.getName(), (String)sex.getSelectedItem());
    hMap.put(address.getName(), address.getText());
    hMap.put(email.getName(), email.getText());
    // Serialize hash map
    WriteObject(hMap);
    // Set trigger
    triggerCls.setTrigger(evt.getActionCommand());
}

Matlab callbacks

The Java GUI sources are compiled and packaged in the statictrigger.jar file. The Matlab StaticButtonTriggerExample.m source file adds the Java library to the dynamic Java classpath:

% Add dynamic java class path
javaclasspath([pwd '\javalib\statictrigger.jar']);

The main.m function contains the code for creating the Java GUI and assigning the static button callback:

% create the statictrigger object
app = statictrigger.app();
% Set static trigger button listener
triggerButton = statictrigger.triggerCls.getTrigger();
buttonProps = handle(triggerButton,'callbackproperties');
set(buttonProps,'ActionPerformedCallback', {@StaticButtonTriggerCallback, app});
% Show the Java Frame
app.setVisible(1);

statictrigger.triggerCls.getTrigger() is a static Java public method that returns the static button object, for which we assign our callback switchyard function.
The following is the StaticButtonTriggerCallback.m code, which displays the information in a Matlab message-box:

% Get action command string
actionCommand = src.getActionCommand();
% Read in serialized hash map
hashMap = app.ReadObject();
% Convert hash map to Matlab structure
data = Hash2Struct(hashMap);
% Display data in Matlab dialog box
msg = ['Name: ' char(hashMap.get('name')) ...
       ', Age: ' num2str(hashMap.get('age')) ...
       ', Sex: ' char(hashMap.get('sex')) ...
       ', Address: ' char(hashMap.get('address')) ...
       ', Email: ' char(hashMap.get('email')) ];
uiwait(helpdlg(msg, 'Form Details'));

You can download the example’s files from here. Extract the zip file, cd to the newly-generated StaticButtonTrigger folder, then invoke the StaticButtonTriggerExample.m function to run the example.

The post Matlab-Java interface using a static control appeared first on Undocumented Matlab.