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Writing Event Listeners
How to Write an Undoable Edit Listener
Undoable edit events occur when an operation that can be undone
occurs on a component.
Currently, only text components fire undoable edit events,
and then only indirectly.
The text component's document fires the events.
For text components,
undoable operations include inserting characters,
deleting characters,
and modifying the style of text.
Programs typically listen to undoable edit events to
assist in the implementation of undo and redo commands.
Here is the undoable edit event handling code from an application
called TextComponentDemo.
...
//where initialization occurs
document.addUndoableEditListener(new MyUndoableEditListener());
...
protected class MyUndoableEditListener implements UndoableEditListener {
public void undoableEditHappened(UndoableEditEvent e) {
//Remember the edit and update the menus
undo.addEdit(e.getEdit());
undoAction.updateUndoState();
redoAction.updateRedoState();
}
}
You can find a link to the source file for
TextComponentDemo in the
example index for Using Swing Components. For a discussion about the undoable edit listener aspect
of the program see
Implementing Undo and Redo
The UndoableEditListener
Interface
Because UndoableEditListener has only one method,
it has no corresponding adapter class.
The UndoableEditEvent Class
| Method |
Purpose |
Object getSource()
(in java.util.EventObject)
|
Return the object that fired the event.
|
|
UndoableEdit getEdit() |
Returns an
UndoableEdit object that represents the edit
that occurred and contains information about and commands
for undoing or redoing the edit.
|
Examples that Use Undoable Edit Listeners
The following table lists the
examples that use undoable edit listeners.
