Intercepting JSplitPane events

There may be situations when you need to know that the divider in a split pane has moved; however, if the online documentation for JSplitPane, you will notice that this class does not offer any method like addChangeListener().

A JSplitPane is really just a container for other components.

If you examine the JComponent class, you will notice a method called addAncestorListener(), which is used to notify a component when its owner has changed.

• In any application supporting a JSplitPane instance, you can implement an AncestorListener for one of the components it owns.
• The interface requires the implementation of three methods, and one of these methods is called to notify the component that its owner (the split pane in this case) has changed.

You can implement this code as follows:

class MyPanel
     extends  JPanel
implements AncestorListener
{
    // Add any special code for this component
    // Ancestor Listener support
    public void ancestorMoved( AncestorEvent event )
       {
           // Add code here to handle a split pane divider movement
         }

   // Not used
   public void ancestorAdded( AncestorEvent event )
     {
      }

   public void ancestorRemoved( AncestorEvent event )
   {
    }
}

The MyPanel class can then be added to one side of the split pane and will faithfully detect any changes to the divider.