Java event propagation stopped

Question

I have a main window:

public class MainPanel extends JFrame implements MouseListener {

   public MainPanel() {
      setLayout(new FlowLayout());
      setDefaultCloseOperation(EXIT_ON_CLOSE);
      addMouseListener(this);

      ChildPanel child = new ChildPanel();
      add(child);

      JPanel spacer = new JPanel();
      spacer.setPreferredSize(new Dimension(50, 50));
      add(spacer);

      pack();
      setLocationRelativeTo(null);
   }

   @Override
   public void mouseClicked(MouseEvent e) {
      System.out.println("Mouse click event on MainPanel");
   }
}

And a child JPanel:

public class ChildPanel extends JPanel implements MouseListener {

   public ChildPanel() {
      setBackground(Color.RED);
      setPreferredSize(new Dimension(200, 200));
      //addMouseListener(this);
   }

   @Override
   public void mouseClicked(MouseEvent e) {
      System.out.println("Mouse click event on ChildPanel");
   }
}

With the call to addMouseListener commented out in the child panel, the parent receives click events when I click anywhere in the window, including on the child. If I uncomment that call and click on the child panel, only the child receives the click event and it doesn't propagate to the parent.

How do I stop the event from being consumed by the child?

Answer 1

In Swing, you generally want the clicked component to respond; but you can forward the mouse event to the parent, as shown below. Here's a related example.

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
import javax.swing.JPanel;

/** @see https://stackoverflow.com/questions/3605086 */
public class ParentPanel extends JPanel {

    public ParentPanel() {
        this.setPreferredSize(new Dimension(640, 480));
        this.setBackground(Color.cyan);
        this.addMouseListener(new MouseAdapter() {

            @Override
            public void mouseClicked(MouseEvent e) {
                System.out.println("Mouse clicked in parent panel.");
            }
        });
        JPanel child = new JPanel();
        child.setPreferredSize(new Dimension(320, 240));
        child.setBackground(Color.blue);
        child.addMouseListener(new MouseAdapter() {

            @Override
            public void mouseClicked(MouseEvent e) {
                System.out.println("Mouse clicked in child panel.");
                ParentPanel.this.processMouseEvent(e);
            }
        });
        this.add(child);
    }

    private void display() {
        JFrame f = new JFrame("MouseEventTest");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(this);
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                new ParentPanel().display();
            }
        });
    }
}