Question

I need to restrict movement of a component (JInternalFrame) inside a JPanel.
More exact: a component should only move along one axis when dragged by the user.

I tried to do it by adding a component listener and reset the position
of one axis everytime the component moves. But it “vibrates”
(moves rapidly during dragging).

I even wrote a custom layout manager, it didn’t help a little!

I guess, the problem is: Both the layout manager and the listener
handle the movement-event after the component is actually moved, right?

Any suggestions?

Should (can I) intercept some event, and modify it, before it’s delivered?

Answer 1

you might want to subclass your InternalFrameUI. I see in BasicInteralFrameUI.BorderListener.mouseDragged(event)(line 885 in version 1.129) a call to getDesktopManager().dragFrame(frame, newX, newY);

You could extend BasicInternalFrameUI to return a custom DesktopManager (extension of DefaultDesktopManager), where in dragFrame() you test the identity of your frame and adjust the axis.

edit:

thinking about it, you are right – it is too complex. as the UI for the internal frame defers to the DesktopManager of the JDesktopPane, you can set it there. here is a poc:

public Demo() {
        JFrame frame = new JFrame();
        frame.setSize(300,300);
        JDesktopPane df = new JDesktopPane();
        DesktopManager dm = df.getDesktopManager();
        df.setDesktopManager(new DefaultDesktopManager(){
               public void dragFrame(JComponent f, int newX, int newY) {
                  super.dragFrame(f, newX, 5);
               }

        });
        JInternalFrame jif = new JInternalFrame("test ");
        jif.setLocation(5, 5);
        jif.setSize(150,100);
        jif.setVisible(true);
        df.add(jif);
        frame.setContentPane(df);
        frame.setVisible(true);
}