从 JButton 创建滑块答案

【问题标题】：create slider from JButton从 JButton 创建滑块
【发布时间】：2014-02-14 16:10:05
【问题描述】：

我在 JPanel 上有 JTextField 和 JButton。我想将监听器添加到JButton，这样当我按下按钮并移动鼠标时，文本字段的值开始改变（当我向右移动鼠标时增加，当我向左移动鼠标时减少）。所以它有点像滑块。这是代码

 final JPanel panel=new JPanel();
 final JTextField text = new JTextField("10");
 JButton button=new JButton("f");
 panel.add(text);
 panel.add(button);

 button.addMouseListener(new MouseAdapter(){
        @Override
        public void mousePressed(final MouseEvent evt){

        //here we add listener to read mouse position when mouse pressed on button
        panel.addMouseListener(new MouseAdapter(){

                int x1 = evt.getXOnScreen();

                int x2;

                @Override
                public void mouseMoved(MouseEvent e){
                    // this method is never called
                    x2=e.getXOnScreen();
                    //increase(decrese) number in textfield by 1% for every moved pixel
                    double d = (x2-x1)*0.01+Double.parseDouble(text.getText());
                    text.setText(Double.toString(d));
                    x1=x2;

                                                    }


                                              });

                        }
       // now, when mouse released we should remove listener from panel
        @Override
        public void mouseReleased(final MouseEvent evt){
            MouseListener[] ml = panel.getListeners(MouseListener.class);
            panel.removeMouseListener(ml[0]);


        }
    });

问题是，panelListener 的 mouseMoved 方法永远不会被调用。我该怎么办？

【问题讨论】：

标签： java swing mouseevent

【解决方案1】：

随便用

panel.addMouseMotionListener(...)

代替：

panel.addMouseListener(...)

来自Java Docs：

公共接口 MouseListener： 用于接收组件上“有趣的”鼠标事件（按下、释放、单击、进入和退出）的侦听器接口。（要跟踪鼠标移动和鼠标拖动，请使用 MouseMotionListener。）

【讨论】：

【解决方案2】：

将MouseMotionListener 添加到您的按钮并使用mouseDragged。坐标可以存储在Point 上的MouseEvent 或MouseListener.mousePressed() 中。这样您就无需添加和删除侦听器：

import java.awt.BorderLayout;
import java.awt.Point;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class Application {

  public static void main(String[] args) {
    final JFrame frame = new JFrame("FrameDemo");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    final JPanel panel = new JPanel();
    final JTextField text = new JTextField("10");
    final JButton button = new JButton("f");
    panel.add(text);
    panel.add(button);
    final Point point1 = new Point();
    final Point point2 = new Point();
    button.addMouseListener(new MouseAdapter() {
      @Override
      public void mousePressed(final MouseEvent evt) {
        point1.x = evt.getXOnScreen();
      }
    });
    button.addMouseMotionListener(new MouseMotionListener() {
      @Override
      public void mouseDragged(MouseEvent e) {
        System.out.println(e);
        point2.x = e.getXOnScreen();
        double d = (point2.x - point1.x) * 0.01 + Double.parseDouble(text.getText());
        text.setText(Double.toString(d));
        point1.x = point2.x;
      }
      @Override
      public void mouseMoved(MouseEvent e) {
      }
    });
    frame.getContentPane().add(panel, BorderLayout.CENTER);
    frame.pack();
    frame.setVisible(true);
  }
}

【讨论】：