Java MouseEvent,检查是否按下了

Question

我有一个实现MouseListener(JPanel)的类.当我点击面板时会发生一些事情.我想要的是某种while循环,只要按下鼠标按钮就会循环.

@Override
public void mousePressed(MouseEvent e) {
    while(e.isPressedDownD) {      // <--
        //DO SOMETHING
    }
}

这显然不起作用,但我希望你理解我正在努力实现的目标.全班有兴趣的人:

package control;

import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import model.GridModel;
import view.GUIView;

public class MapListener implements MouseListener{
    private GridModel model;
    private GUIView view;
    private int posX;
    private int posY;

    public MapListener(GridModel model, GUIView view) {
        this.model = model;
        this.view = view;
    }

    @Override
    public void mouseClicked(MouseEvent e) {
        posX = e.getX();
        posY = e.getY();
        model.setMouseAtX(posX);
        model.setMouseAtY(posY);
        view.paintTile();
        System.out.println("X: " + posX + " Y: " + posY);
    }

    @Override
    public void mouseEntered(MouseEvent e) {
    }

    @Override
    public void mouseExited(MouseEvent arg0) {
    }

    @Override
    public void mousePressed(MouseEvent e) {
        while(e.getModifiers() == MouseEvent.MOUSE_PRESSED) { //Obviously doesn't work
            //DO SOMETHING
        }
    }

    @Override
    public void mouseReleased(MouseEvent arg0) {
    }
}

Answer 1

正如其他答案所指出的,完成工作的地方不在鼠标事件监听器方法中.

此外,没有明确的"鼠标按下"概念MouseEvent,因此您必须自己跟踪.我提供了一个如何执行此操作的示例.还要注意MouseEvent.BUTTON1引用,因为这只是为了跟踪鼠标左键的状态.

这是您必须开始学习并发性的地方.出于这个原因,我已经添加了一个synchronized方法,因为你需要知道当多个线程同时访问属性时会发生有趣的事情,并且这synchronized是一种保持理智的机制.考虑进一步阅读超出本示例的范围.

未经测试,但这应该工作:

volatile private boolean mouseDown = false;

public void mousePressed(MouseEvent e) {
    if (e.getButton() == MouseEvent.BUTTON1) {
        mouseDown = true;
        initThread();
    }
}

public void mouseReleased(MouseEvent e) {
    if (e.getButton() == MouseEvent.BUTTON1) {
        mouseDown = false;
    }
}

volatile private boolean isRunning = false;
private synchronized boolean checkAndMark() {
    if (isRunning) return false;
    isRunning = true;
    return true;
}
private void initThread() {
    if (checkAndMark()) {
        new Thread() {
            public void run() {
                do {
                    //do something
                } while (mouseDown);
                isRunning = false;
            }
        }.start();
    }
}

Answer 2

为什么这么多答案错误地断言MouseEvent中没有明确的"鼠标按下"概念？

虽然其他评论者是正确的,OP不应该在事件处理程序中执行所有这些操作,但在其他情况下,查询鼠标侦听器中的按钮状态是有用的.在这些情况下,您实际上可以确定按钮关闭状态.例如:

@Override
public void mouseExited(MouseEvent event) // Or any other mouse event handler...
{
    int buttonsDownMask = MouseEvent.BUTTON1_DOWN_MASK 
            | MouseEvent.BUTTON2_DOWN_MASK 
            | MouseEvent.BUTTON3_DOWN_MASK; // Or whichever buttons you care about...
    if ( (event.getModifiersEx() & buttonsDownMask) != 0 )
        System.out.println("Hey! Some button is pressed!");
}

特别注意该MouseEvent.getModifiersEx()方法的使用,以及MouseEvent.BUTTON1_DOWN_MASK和朋友一起使用.