调用 frame.setLocation() 时触发 Java mouseExited 事件

Question

我有一个没有装饰（没有标题栏、关闭按钮等）的 JFrame，我可以使用 setLocation() 和鼠标位置在屏幕上拖动它。

不幸的是，第一次移动窗口时会调用 mouseExited 事件...

1. 将鼠标移入窗口并触发 mouseEntered 事件
2. 单击鼠标并触发 mousePressed 事件。
3. 拖动鼠标并触发 mouseDragged 事件，并调用 setLocation。
4. mouseExited 事件被触发，即使鼠标仍在窗口中！
5. 此时将鼠标移出窗口不会触发 mouseExited。
6. 将鼠标移出和移入将重置回第 1 步。

除了手动测试鼠标在屏幕上的位置之外，我该如何解决这个问题？

编辑：这是代码的精简版

import java.awt.*;
import javax.swing.*;
import java.awt.Event;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;

import javax.swing.JComponent;
import javax.swing.JFrame;

class DragNDropper implements MouseMotionListener, MouseListener
{
    private int x, y;
    private int dx, dy;

    private boolean clicked;

    private JFrame frame;

    public DragNDropper(JFrame frame)
    {
    dx = dy = 0;
    this.frame = frame;
    }

    public void mouseDragged(MouseEvent e)
    {
    x = e.getXOnScreen();
    y = e.getYOnScreen();

    frame.setLocation(x-dx, y-dy);
    }

    public void mouseMoved(MouseEvent e)
    {
    x = e.getXOnScreen();
    y = e.getYOnScreen();
    }

    public void mouseClicked(MouseEvent e)
    {

    }

    public void mousePressed(MouseEvent e)
    {
    clicked = true;
    dx = e.getX();
    dy = e.getY();
    }

    public void mouseReleased(MouseEvent e)
    {
    clicked = false;
    }

    public void mouseEntered(MouseEvent e)
    {
    System.out.println("Mouse entered");
    }


    public void mouseExited(MouseEvent e)
    {
    System.out.println("Mouse exited");
    }
}


public class Program
{
public static void main(String[] argv)
{
JFrame jf = new JFrame();
DragNDropper dnd = new DragNDropper(jf);

jf.setSize(new Dimension(512, 512));
jf.addMouseListener(dnd);
jf.addMouseMotionListener(dnd);

jf.show();
}
}

Answer 1

使用此代码一切正常。请停止使用frame.show()，从那里您得知这是用于显示JFrame，改用frame.setVisible(true)。请多解释一下这个问题。请看一下这段代码的修改：

import java.awt.*;
import java.awt.Event;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import javax.swing.*;

public class DragNDropper implements MouseMotionListener, MouseListener {

    private int x, y;
    private int dx, dy; 
    private boolean clicked;    
    private JFrame jf;

    public static void main(String[] argv) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                new DragNDropper().displayGUI();
            }
        });
    }

    private void displayGUI() {
        dx = dy = 0;
        jf = new JFrame();
        jf.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        jf.setUndecorated(true);

        jf.setSize(new Dimension(512, 512));
        jf.addMouseListener(this);
        jf.addMouseMotionListener(this);

        jf.setVisible(true);
    }

    public void mouseDragged(MouseEvent e) {
        x = e.getXOnScreen();
        y = e.getYOnScreen();
        jf.setLocation(x-dx, y-dy);
    }

    public void mouseMoved(MouseEvent e) {
        x = e.getXOnScreen();
        y = e.getYOnScreen();
    }

    public void mouseClicked(MouseEvent e) {
    }

    public void mousePressed(MouseEvent e) {
        clicked = true;
        dx = e.getX();
        dy = e.getY();
    }

    public void mouseReleased(MouseEvent e) {
        clicked = false;
    }

    public void mouseEntered(MouseEvent e) {
        System.out.println("Mouse entered");
    }

    public void mouseExited(MouseEvent e) {
        System.out.println("Mouse exited");
    }
}