在底层组件上触发鼠标事件

Question

I'm looking for a way to pass mouse events to components covered by other components. To illustrate what I mean, here's a sample code. It contains two JLabel s, one is twice smaller and entirely covered with a bigger label. If you mouse over the labels, only the bigger one fires mouseEntered event however.

import java.awt.Color;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.WindowConstants;
import javax.swing.border.LineBorder;

public class MouseEvtTest extends JFrame {

    public MouseEvtTest() {
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        setLayout(null);
        setSize(250, 250);

        MouseAdapter listener = new MouseAdapter() {
            @Override
            public void mouseEntered(MouseEvent e) {
                System.out.printf("Mouse entered %s label%n", e.getComponent().getName());
            }
        };
        LineBorder border = new LineBorder(Color.BLACK);

        JLabel smallLabel = new JLabel();
        smallLabel.setName("small");
        smallLabel.setSize(100, 100);
        smallLabel.setBorder(border);
        smallLabel.addMouseListener(listener);
        add(smallLabel);

        JLabel bigLabel = new JLabel();
        bigLabel.setName("big");
        bigLabel.setBorder(border);
        bigLabel.setSize(200, 200);
        bigLabel.addMouseListener(listener);
        add(bigLabel, 0); //Add to the front
    }

    public static void main(String[] args) {
        new MouseEvtTest().setVisible(true);
    }
}

What would be the best way to fire mouse entered event on the smaller label when cursor is moved to the coordinates above it? How would it work in case where there would be multiple components stacked on top of each other? What about the remaining mouse events, like mouseClicked , mousePressed , mouseReleased , etc.?

Answer 1

In your listener:

bigLabel.dispatchEvent(mouseEvent);

Of course, you will have to define bigLabel as final

Answer 2

看看 Alexander Potochkin 在A Well-Behaved GlassPane上的博客条目

Answer 3

Well to understand whats happening you need to understand how Z-Ordering works. As a quick overview, the component that was added last is painted first. So in your case you want to add the small component before the big component.

// add(bigLabel, 0); //Add to the front
add(bigLabel); // add to the end so it is painted first

The OverlayLayout might help explain this better and give you another option.