UndoManager manually add UndoableEdit to make it work with JTabbedPane

Question

Edit : please, have a look at the end of the post...

To begin, please excuse me for my bad english...

I'm trying to make a text editor in Java, using a JTabbedPane to edit multiple files. I have found no good help on the Internet to use UndoManager in that case.

So I tried something but it doesn't seem to work.

In fact, I tried to save all UndoableEdit by listening when I change tab. When I change tab, I save the UndoableEdits for the previously opened tab, then I clean the edits of the UndoManager and finaly, I restore the UndoableEdits of the new active tab.

The problem I have is that when I call the function that updates the undo/redo button state, the canUndo()/canRedo() methods always return false, but there are edits in the list... And I don't know why this happens, I don't understand what I forgot to do...

Obviously, however present the UndoableEdits are present in the "edits" Vector, UndoManager doesn't care of this. When I tried to force the buttons to be enabled, an exception throws... (javax.swing.undo.CannotUndoException / javax.swing.undo.CannotRedoException)

Could you help me please ?

Don't hesitate to ask me for further information if you need it.

Thank you.

My extension of the UndoManager class :

public class UndoManagerPerso extends UndoManager
{
private static final long serialVersionUID = 8386145389216281754L;


public ArrayList<UndoableEdit> getEdits()
{
    ArrayList<UndoableEdit> listEdits = new ArrayList<UndoableEdit>();

    listEdits.addAll(this.edits);

    return listEdits;
}

public void setEdits(ArrayList<UndoableEdit> listEdits)
{
    for(UndoableEdit ue:listEdits)
    {
        this.addEdit(ue);
    }
}

}

The call of these functions, in my main window's class :

    tabbedPane_editeur.addChangeListener(new ChangeListener()
    {
        @Override
        public void stateChanged(ChangeEvent e)
        {
            if (e.getSource() instanceof JTabbedPane)
            {
                JTabbedPane pane = (JTabbedPane) e.getSource();
                int previousTab = f_principale.this.activeTab;
                int activeTab = pane.getSelectedIndex();

                System.out.println("Selected paneNo : " + pane.getSelectedIndex() + ", précédent : " + previousTab);

                f_principale.this.listEditeurs.get(previousTab).setListEdits( f_principale.this.undoManager.getEdits());
                f_principale.this.undoManager.setEdits(f_principale.this.listEditeurs.get(activeTab).getListEdits());

                f_principale.this.activeTab = activeTab;

                f_principale.this.updateButtons();
            }
        }

    });
public void updateButtons()
 {
     this.btnUndo.setText(undoManager.getUndoPresentationName());
     this.btnRedo.setText(undoManager.getRedoPresentationName());
     this.btnUndo.setEnabled(undoManager.canUndo());//returns false
     this.btnRedo.setEnabled(undoManager.canRedo());//returns false
 }

Edit : (1 day later) I have tested the UndoManader again today, and I noticed something. In fact, insert manually the UndoableEdit works ! But the number of edits increases too quickly to be normal...

I reach the default limit (100) quickly and that's why I thought it wasn't working at all yesterday : when the limit is reached, canUndo() / canRedo() seem to return false and when the button are forced to be enabled, exceptions are thrown.

Maybe when I switch tab, something wrong happens... But what ? Do you have any idea ? I'm going to have a look at this...

Answer 1

You should create a separate UndoManager for each Tab.