Question

我无法弄清楚为什么我写的这个简单程序在鼠标离开跟踪区域（白色JPanel）时尝试更新鼠标坐标时会得到一个IndexOutOfBounds异常。我认为第38行的检查会照顾它。有什么建议？谢谢！

import java.awt.*;

import javax.swing.JFrame;

public class MainFrame extends JFrame {

    private static final long serialVersionUID = 1L;

    Label coorLabel;
    Panel coorPanel, content;

    public MainFrame(String s){

        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        Container cont = getContentPane();

        coorLabel = new Label("Mouse Coordinates: ");

        coorPanel = new Panel();
        coorPanel.setPreferredSize(new Dimension(400,400));
        coorPanel.setBackground(Color.WHITE);
        /**
        content = new Panel();
        content.add(coorPanel, BorderLayout.PAGE_START);
        content.add(coorLabel, BorderLayout.PAGE_END);
        **/

        cont.add(coorPanel, BorderLayout.PAGE_START);
        cont.add(coorLabel, BorderLayout.PAGE_END);

        pack();
        setVisible(true);

    }

    public void updateCoor(){

        if(coorPanel.getMousePosition()!=null){
            coorLabel.setText("Mouse Coordinates: "+getMousePosition().x+", "+getMousePosition().y);
            coorLabel.repaint();
        }

    }

    public static void main(String[]args){

        MainFrame frame = new MainFrame("Coor App");
        while(true){
            frame.updateCoor();
        }

    }

}

Answer 1

查看Concurrency in Swing教程。你正在完全占据初始带有while(true)循环的线程并更新事件调度线程之外的用户界面。

请参阅Introduction to Event Listeners以熟悉Swing事件模型，特别是How to Write a Mouse-Motion Listener以了解鼠标移动侦听器示例。

Answer 2

您检查coorPanel.getMousePosition()是否为空，然后引用（此。）getMouseLocation();尝试将其改为仅在支票中说出getMousePosition，并添加一个打印：

if( this.getMousePosition() != null ){
    System.out.println(getMousePosition());
    coorLabel.setText("Mouse Coordinates: "+getMousePosition().x+", "+getMousePosition().y);
    coorLabel.repaint();
}

Answer 3

这是你应该做的：

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;
import javax.swing.*;

public class Stack extends JFrame implements MouseMotionListener{
    int x;
    int y;
    JPanel p = new JPanel();
    JPanel detectPanel = new JPanel();
    JTextField t = new JTextField(10);
    JLabel l = new JLabel("Position's inside of bordered panel: ");
    public Stack(){
        setLayout(new BorderLayout());
        t.setEditable(false);
        p.add(l);
        p.add(t);
        detectPanel.setBorder(BorderFactory.createLineBorder(Color.BLACK));
        add(p,BorderLayout.NORTH);
        add(detectPanel,BorderLayout.CENTER);
        detectPanel.addMouseMotionListener(this);

    }

    public static void main(String[] a){
        SwingUtilities.invokeLater(new Runnable(){
            public void run(){
                Stack s = new Stack();
                s.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                s.setLocationByPlatform(true);
                s.setPreferredSize(new Dimension(640,480));
                s.pack();
                s.setVisible(true);
            }
        });
    }

    public void mouseDragged(MouseEvent e) {

    }

    public void mouseMoved(MouseEvent e) {
        x= e.getX();
        y= e.getY();
        t.setText(x+", "+y);
    }
}

IndexOutOfBounds使用swing gui跟踪鼠标

3 个答案: