javax.swing.undo.UndoManager & javax.swing.JMenuItem

[Ricardo Wagemaker]

Can someone explain what I am missing and why this is not working? I am not going to paste the whole class as it's 1500 lines.

While it works using short cut keys example:
GOOD CODE FOR Keyboard short-cut

 final UndoManager undoManager = new UndoManager(); //TODO
 textComp = createTextComponent();
 textComp.getDocument().addUndoableEditListener(undoManager);
 InputMap im = textComp.getInputMap(JComponent.WHEN_FOCUSED);
 ActionMap am = textComp.getActionMap();
 im.put(KeyStroke.getKeyStroke(KeyEvent.VK_Z, Toolkit.getDefaultToolkit().getMenuShortcutKeyMask()), "Undo");
 im.put(KeyStroke.getKeyStroke(KeyEvent.VK_Y, Toolkit.getDefaultToolkit().getMenuShortcutKeyMask()), "Redo");

 am.put("Undo", new AbstractAction() {
	private static final long serialVersionUID = 1L;

		@Override
	    public void actionPerformed(ActionEvent e) {
	        try {
	            if (undoManager.canUndo()) {
	                undoManager.undo();
	            }
	        } catch (CannotUndoException exp) {
	            exp.printStackTrace();
	        }
	    }
	});
	am.put("Redo", new AbstractAction() {
		private static final long serialVersionUID = 1L;

		@Override
	    public void actionPerformed(ActionEvent e) {
	        try {
	            if (undoManager.canRedo()) {
	                undoManager.redo();
	            }
	        } catch (CannotUndoException exp) {
	            exp.printStackTrace();
	        }
	    }
	});

I am now trying to add/use the JMenuItem with the following code and I can't understand why this is not working as it looks all good too me.

CODE NOT WORKING VIA MENU

// Set it up
 final UndoManager undoManager = new UndoManager(); //TODO
 textComp = createTextComponent();
 textComp.getDocument().addUndoableEditListener(undoManager);
 JMenuItem mnuUndo = new JMenuItem("Undo", new ImageIcon(getClass().getResource("/undo.png")));
 mnuUndo.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_Z, Toolkit.getDefaultToolkit().getMenuShortcutKeyMask()));

// add to the menu
edit.add(mnuUndo);

// ActionListener
 mnuUndo.addActionListener(new ActionListener() {
	 @Override
	    public void actionPerformed(ActionEvent e) {
	        try {
	        	System.out.println("trying");
	            if (undoManager.canUndo()) {
	                undoManager.undo();
	                System.out.println("Undone");
	            }
	        } catch (CannotUndoException exp) {
	            exp.printStackTrace();
	        }
	    }
	});

I have no error actually System.out.println("trying"); shows when button is pressed but for some reason undoManager.canUndo() is not valid.

Any help would be greatly appreciated as I am sure it's something simple I forgot or can't see at the moment.

[Rob Camick]

Your basic approach is wrong.

The benefit of using an Action is that it can be shared by any component that supports Actions.

So instead of trying to implement multiple annonymous inner classes, you should be creating a single Action. Then you can create your JMenuItem with this Action.

Another benefit of using the Action is that you can assign the accelerator and mnemonic keys directly to the Action. Swing will then do the Keystroke bindings for you automatically when you create the menu item.

Read the section from the Swing tutorial on How to Use Actions for more information. There is also a section on Text Component Features that demos  working undo/redo Actions.