java 为什么在使用 MouseAdapter 时没有收到 mouseDragged 事件？

Why are mouseDragged-events not received when using MouseAdapter?

提问by Tim

Why are mouseDragged-events only received when using MouseMotionAdapter
and not when using MouseAdapter?

为什么mouseDragged-events 只在使用MouseMotionAdapter
时接收，而在使用时不接收MouseAdapter？

Java has two abstract adapter classes for receiving mouse-events ;
MouseAdapterand MouseMotionAdapter.

Java 有两个抽象适配器类用于接收鼠标事件；
MouseAdapter和MouseMotionAdapter。

Both classes have a mouseDragged(MouseEvent e)-method, but the
one in MouseAdapterdoes not seem to work ; mouseDragged-events
never get through with this one.

两个类都有一个mouseDragged(MouseEvent e)-method，但
一个 inMouseAdapter似乎不起作用；mouseDragged- 事件
永远无法解决这个问题。

Both classes implement the MouseMotionListener-interface which
defines the mouseDragged-event, so I don't understand why it is
not working correctly on both of them.

这两个类都实现了MouseMotionListener其γ-接口
定义了mouseDragged-event，所以我不明白为什么它
不能在他们两人的正常工作。

Here is sample-code which shows this issue :

这是显示此问题的示例代码：

import java.awt.event.MouseAdapter;  
import java.awt.event.MouseEvent;  
import java.awt.event.MouseMotionAdapter;  
import javax.swing.JFrame;  

public class SwingApp extends JFrame
{
    public SwingApp()
    {   
        // No mouseDragged-event is received when using this : 
    this.addMouseListener(new mouseEventHandler()); 

    // This works correct (when uncommented, of course) :
    // this.addMouseMotionListener(new mouseMovedEventHandler());


    setBounds(400,200, 550,300);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setResizable(false);
    setVisible(true);
    }   

  public static void main(String args[])
  {
    new SwingApp();
  }

  class mouseEventHandler extends MouseAdapter
  {         
    @Override
    public void mouseDragged(MouseEvent e) // Why is this method never called ?
    {
        System.out.println(String.format("MouseDragged via MouseAdapter / X,Y : %s,%s ", e.getX(), e.getY()));
    }
  } 

  class mouseMovedEventHandler extends MouseMotionAdapter
  {           
    @Override
    public void mouseDragged(MouseEvent e)
    {
        System.out.println(String.format("MouseDragged via MouseMotionAdapter / X,Y : %s,%s ", e.getX(), e.getY()));
    }
  } 

}

回答by aioobe

If you add it through

如果你通过添加它

this.addMouseListener(new mouseEventHandler()); 

you will not receive motion related MouseEvents(That's not what you registered the listener for!)

你不会收到相关的动作MouseEvents（那不是你注册监听器的目的！）

You'll have to add the listener twice, i.e., add it using addMouseMotionListeneras well:

您必须添加两次侦听器，即也使用以下addMouseMotionListener方法添加它：

mouseEventHandler handler = new mouseEventHandler();
this.addMouseListener(handler); 
this.addMouseMotionListener(handler);

in order to get both type of events.

为了获得这两种类型的事件。

(A side node, always use a capital first letter for your classes, i.e., use MouseEventHandlerinstead :-)

（一个侧节点，总是为你的类使用大写的第一个字母，即使用MouseEventHandler:-)

回答by iluxa

you gotta add your MouseAdapter as both mouseListener and mouseMotionListener, and you'll be golden. MouseAdapter implements both MouseListener and MouseMotionListener, but your component doesn't know to pass mouseDragged events to it unless you call addMouseMotionListener

你必须将你的 MouseAdapter 添加为 mouseListener 和 mouseMotionListener，你会很高兴。MouseAdapter 实现了 MouseListener 和 MouseMotionListener，但是除非您调用 addMouseMotionListener，否则您的组件不知道将 mouseDragged 事件传递给它

回答by jvn91173

The top answers for this question are now pretty old. For anyone using Java JDK 8 or later, be sure to check out https://docs.oracle.com/javase/tutorial/uiswing/events/mousemotionlistener.html.

这个问题的最佳答案现在已经很老了。对于使用 Java JDK 8 或更高版本的任何人，请务必查看https://docs.oracle.com/javase/tutorial/uiswing/events/mousemotionlistener.html。

To summarize, your listener class has to extend from MouseInputAdapterinstead of MouseMotionAdapteror MouseAdapter. You'll add your listener class using addMouseMotionListenerand addMouseListeneras follows:

总而言之，您的侦听器类必须从而MouseInputAdapter不是MouseMotionAdapteror扩展MouseAdapter。您将使用addMouseMotionListener和添加您的侦听器类addMouseListener，如下所示：

MyMouseHandler myMouseHandler = new MyMouseHandler ();
addMouseMotionListener(myMouseHandler);
addMouseListener(myMouseHandler);