Respond to events in other JPanels

Question

Ok so lets say I have 3 Jpanels - 1 parent and 2 Children

//Assume necessary imports etc

parent is something like:

public class ParentPanel extends JFrame  {
private JPanel mainPanel,controlPanel;

public ParentPanel(){
    MainPanel pp= new ParentPanel();
    controlPanel cp = new controlPanel();
}
...

Main Panel in real thing is like a 2d graphics thing but not important for the point so simplified:

public class MainPanel implements MouseMotionListener{
    public MainPanel(){
        //not important now 
    }

    public void MouseMoved(MouseEvent arg0){
        int xPos e.getX
    }
...

What i want to do is get the X pos of the mouse and pass it from main panel up to the parent and into a label for example on the sibling control panel.

Any ideas clues or pointers appreciated thanks

Answer 1

You could write a pass-through listener. Something in the child panel that the parent can listen too. Then when the child received a mouse moved event it would broadcast it back up to the parent.

You could also make the label on the sibling control panel into a small model object. Then both of the children listeners would know about the model object. One child would modify it and the other would listen for updates.

Answer 2

You could create an interface that is notified of the changes which ParentPanel can then implement and MainPanel can use to pass the message along.

interface XPositionListener {
    void updateXPosition(int xPos);
}  

public class ParentPanel extends JFrame implements XPositionListener  {
    private MainPanel mainPanel; private ControlPanel controlPanel;

    public ParentPanel() {
        mainPanel = new MainPanel(this);
        controlPanel = new ControlPanel();
    }

    void updateXPosition(int xPos) {
        // Update a label or whatever
    }   

    // ...
}

public class MainPanel implements MouseMotionListener {
    XPositionListener listener;

    public MainPanel(XPositionListener listener) {
         this.listener = listener;
    }

    public void MouseMoved(MouseEvent event) {
        int xPos = event.getPoint().x;
        listener.updateXPosition(xPos);
    }

    // ...
}

Check out the Observer Pattern for information on a more robust solution.

Answer 3

Depending on how complicated the GUI is you can pass the ParentPanel object as a parameter to the MainPanel object. In the MainPanel you have access to all the ParentPanel's components etc.

 public class MainPanel implements MouseMotionListener{

 ParentPanel parent;

 public MainPanel(ParentPanel p){
    //not important now
    parent = p; 
 }

 public void MouseMoved(MouseEvent arg0){
    //Access to parent here.
 }

And in the ParentPanel when you create teh MainPanel:

MainPanel pp= new MainPanel(this);

This is of course a very simple solution and more complicated GUIs will not be suitable.