Java AWT：如何知道在 mouseDragged 事件后释放了哪个鼠标按钮？答案

【问题标题】：Java AWT: How to know which mouse button was released after a mouseDragged event?Java AWT：如何知道在 mouseDragged 事件后释放了哪个鼠标按钮？
【发布时间】：2018-03-15 05:33:41
【问题描述】：

如果我按住两个鼠标按钮，然后拖动鼠标，然后释放其中一个按钮，我如何确定哪个按钮被释放？按下的按钮可以通过 MouseEvent.getModifiersEx() 检索，但似乎没有任何方法可以判断哪个按钮被释放，因为在释放事件触发之前按下的所有按钮都存储在该掩码中：

public void mouseReleased(MouseEvent e) {

    int b1 = MouseEvent.BUTTON1_DOWN_MASK;
    int b2 = MouseEvent.BUTTON2_DOWN_MASK;

    System.out.println(e.getButton()) // prints "0" when the mousereleased
                                      // event follows a mouseDragged
                                      // event

    if ((mouseEvent.getModifiersEx() & b1) == b1) {
      System.out.println("button 1 released");
    } else if ((mouseEvent.getModifiersEx() & b2) == b2) {
      System.out.println("button 2 released");
    }

    /* 
       Following a mouseDragged event, assuming button 1 and button 2 
       were pressed before either was released, the first if clause 
       evaluates to true regardless of which button was actually released.
       In other words, releasing button 2 in this scenario will print
       "button 1 released"
     */

}

如果 mouseReleased 事件之前有 mousePressed 事件很容易，但是当它之前有 mouseDragged 时，我不能简单地调用 getButton()...

【问题讨论】：

请发布您最好的minimal reproducible example 尝试向我们展示您的代码是如何正常工作的。
你试过SwingUtilities#isLeftMouseButton和isRightMouseButton吗？
@HovercraftFullOfEels 感谢您的反馈。我用一个具体的代码块替换了抽象代码块，以更好地说明我的问题。
谢谢，它有效。我不知道为什么我认为 getButton 在之前的拖动事件之后返回 0。

标签： java events awt mouse

【解决方案1】：

但是当它前面有mouseDragged时，我不能简单地调用getButton()...

为什么不呢？

如果您想要在拖动停止后鼠标释放的状态，也许在您的 MouseAdapter 中使用一个布尔标志，并在拖动时将其设置为 true。比如：

import java.awt.Dimension;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;

import javax.swing.*;

public class MouseButtons extends JPanel {
    private static final int PREF_W = 800;
    private static final int PREF_H = 650;

    public MouseButtons() {
        MyMouseAdapter myMouse = new MyMouseAdapter();
        addMouseListener(myMouse);
        addMouseMotionListener(myMouse);
    }

    @Override
    public Dimension getPreferredSize() {
        if (isPreferredSizeSet()) {
            return super.getPreferredSize();
        }
        return new Dimension(PREF_W, PREF_H);
    }

    private class MyMouseAdapter extends MouseAdapter {
        private boolean dragging = false;

        @Override
        public void mousePressed(MouseEvent e) {
        }

        @Override
        public void mouseReleased(MouseEvent e) {
            String text = "";
            int button = e.getButton();
            if (button == MouseEvent.BUTTON1) {
                text = "Button 1";
            } else if (button == MouseEvent.BUTTON2) {
                text = "Button 2";
            } else if (button == MouseEvent.BUTTON3) {
                text = "Button 3";
            }

            if (dragging) {
                System.out.println(text + " just finished dragging");
            } else {
                System.out.println(text + " not recently dragging");
            }
            dragging = false;
        }

        @Override
        public void mouseDragged(MouseEvent e) {
            dragging = true;
        }
    }

    private static void createAndShowGui() {
        JFrame frame = new JFrame("MouseButtons");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(new MouseButtons());
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> createAndShowGui());
    }
}

除非我完全误解了你的问题，如果是这样，我请你澄清一下。

【讨论】：