一旦 JLayeredComponent 将它们移动到前层，组件就会回到原点

问题描述

我有一个程序，当您单击并拖动按钮时，它会将按钮移动到屏幕的前面。问题在于，一旦分层窗格将组件添加到其他层之上的层，它就会将组件移回 JFrame 的原点。

package Control;

import java.awt.Color;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;

import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JlayeredPane;

public class layeredPaneTest {
static JlayeredPane layeredPane;

static int screenX;
static int screenY;

public static MouseListener getMouseListener(JComponent component) {
    MouseListener mListener = new MouseListener() {
        @Override
        public void mouseClicked(MouseEvent e) {}

        @Override
        public void mousepressed(MouseEvent e) {
            screenX = e.getXOnScreen();
            screenY = e.getYOnScreen();

            layeredPane.add(component,new Integer(1),0); //this method is the one that makes the component go back to the origin
            //If I delete this method,the buttons no longer go back to the origin,but the layered obvIoUsly doesn't work
            //I've tried adding a setBounds method here for component,but it still goes back to the origin
        }

        @Override
        public void mouseReleased(MouseEvent e) {}

        @Override
        public void mouseEntered(MouseEvent e) {}

        @Override
        public void mouseExited(MouseEvent e) {}
    };
    return mListener;
}

public static MouseMotionListener getMouseMotionListener(JComponent component) {
    MouseMotionListener mmListener = new MouseMotionListener() {
        @Override
        public void mouseDragged(MouseEvent e) {
            int deltaX = e.getXOnScreen() - screenX;
            int deltaY = e.getYOnScreen() - screenY;
                
            component.setLocation(deltaX,deltaY);
        }

        @Override
        public void mouseMoved(MouseEvent e) {}

    };
    return mmListener;
}

private static void createAndShowGUI() {
    JFrame frame = new JFrame();
    frame.setLocation(0,0);
    frame.setSize(400,400);
    frame.setVisible(true);
    
    layeredPane = new JlayeredPane();
    
    JButton button1 = new JButton("JButton 1");
    button1.setBackground(Color.RED);
    button1.setSize(100,50);
    button1.addMouseListener(getMouseListener(button1));
    button1.addMouseMotionListener(getMouseMotionListener(button1));
    layeredPane.add(button1,new Integer(0),0);
    button1.setBounds(0,button1.getWidth(),button1.getHeight());
    
    JButton button2 = new JButton("JButton 2");
    button2.setBackground(Color.BLUE);
    button2.setSize(100,50);
    button2.addMouseListener(getMouseListener(button2));
    button2.addMouseMotionListener(getMouseMotionListener(button2));
    layeredPane.add(button2,0);
    button1.setBounds(100,100,button2.getWidth(),button2.getHeight());
    
    JButton button3 = new JButton("JButton 3");
    button3.setBackground(Color.GREEN);
    button3.setSize(100,50);
    button3.addMouseListener(getMouseListener(button3));
    button3.addMouseMotionListener(getMouseMotionListener(button3));
    layeredPane.add(button3,0);
    button1.setBounds(200,200,button3.getWidth(),button3.getHeight());
    
    frame.add(layeredPane);
}

public static void main(String[] args) {
    //Schedule a job for the event-dispatching thread:
    //creating and showing this application's GUI.
    javax.swing.SwingUtilities.invokelater(new Runnable() {
        public void run() {
            createAndShowGUI();
        }
   }); 
}
}

我花了很多时间尝试切换方法、测试等等，但问题依赖于方法 layeredPane.add(component,0);。我对 JlayeredPanes 很陌生，所以一定有我遗漏的地方。

解决方法

问题不在于 layeredPane.add() 方法，而在于您计算新组件位置的方式。

假设按钮是一个位置，因此当您在 (200,100) 位置单击时，您会按下按钮。在那一刻，您存储了 screenX=200; screenY=100;。

如果您现在将鼠标移动到 (210,100)，您将新位置计算为 deltaX = 210-200; 和 deltaY = 100 - 100;，从而将组件放置在左上角。

---

您可能应该在 mousePressed 事件上存储鼠标相对于组件的偏移量，并在 mouseDragged 事件上为该偏移量调整组件位置：

static int offsetX;
static int offsetY;

public static MouseListener getMouseListener(JComponent component) {
    // [...]
    @Override
    public void mousePressed(MouseEvent e) {
        offsetX = e.getXOnScreen() - component.getX();
        offsetY = e.getYOnScreen() - component.getY();

        layeredPane.add(component,new Integer(1),0);
    }
    // [...]
}

public static MouseMotionListener getMouseMotionListener(JComponent component) {
    MouseMotionListener mmListener = new MouseMotionListener() {
        @Override
        public void mouseDragged(MouseEvent e) {
            int posX = e.getXOnScreen() - offsetX;
            int posY = e.getYOnScreen() - offsetY;
            
            component.setLocation(posX,posY);
        }
        // [...]
    };
    return mmListener;
}