在JPanel中移动图形 [英] Moving Graphics in JPanel

问题描述

当单击按钮时，我想在JPanel中将椭圆形从一个位置移动到另一个位置.这是我想出的代码.但是，当我单击按钮时，所有这些都立即发生，并且没有可见的移动，从开始到结束的速度都很慢.椭圆形刚刚出现在新位置.

I'll like to make an Oval move from one place to the other in a JPanel when a button is clicked. This is the code I came up with. When I click the button however it all happens at once without visible movement the slow from the start to finish seen. The Oval just appears in a new location.

import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;
import javax.swing.JPanel;
public class testtest implements ActionListener{
    JButton button;
    MyDrawPanel panel;
    int x = 0;
    int y = 0;
    public static void main(String[]args){
        testtest test = new testtest();
        test.go();
    }
    public void go(){
        JFrame frame = new JFrame("Balloon Balls");
        panel = new MyDrawPanel();
        button = new JButton("Restart");
        button.addActionListener(this);
        panel.add(button);
        frame.setSize(300, 300);
        frame.add(panel);
        frame.setVisible(true);
    }

    @Override
    public void actionPerformed (ActionEvent e){
        for(int i=0;i<130;i++){
            x++;
            y++;
            panel.repaint();
            try {
                Thread.sleep(100);
            } catch(Exception ex) { }
        }
    }
    class MyDrawPanel extends JPanel{
        @Override
        public void paintComponent(Graphics g){
            g.fillOval(x, y, 30, 30);
            g.setColor(Color.BLACK);

        }
    }
}

推荐答案

Swing是单线程且不是线程安全的.

Swing is single thread AND not thread safe.

在ActionListener中使用Thread.sleep(100)阻止了事件分发线程，从而阻止了任何内容的绘制.直到actionPerformed方法存在之后，才会进行新的绘画遍历.

Using Thread.sleep(100) within the ActionListener is blocking the Event Dispatching Thread, preventing anything from been painted. A new paint pass won't occur until after the actionPerformed method exists.

有关更多详细信息，请参见 Swing中的并发.

See Concurrency in Swing for more details.

Swing也不是线程安全的，这意味着您永远不应在EDT上下文之外对UI进行更改.

Swing is also not thread safe, this means you should never make changes to the UI from outside the context of the EDT.

最简单的解决方案是使用 Swing Timer ，它将允许建立定时定时的回调，这些回调在事件调度线程中执行，但不会阻止EDT.

The easiest solution is to make use of a Swing Timer, which will allow to establish regularly timed callbacks, which are executed within the Event Dispatching Thread, but which won't block the EDT.

您还缺少OO的重要概念之一，即封装. x/y属性实际上应该由MyDrawPanel而不是testtest

You're also missing one of the important concepts of OO, encapsulation. The x/y properties should actually be managed by the MyDrawPanel, not testtest

例如...

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;

public class testtest implements ActionListener {

    JButton button;
    MyDrawPanel panel;

    public static void main(String[] args) {
        testtest test = new testtest();
        test.go();

    }

    public void go() {
        JFrame frame = new JFrame("Balloon Balls");
        panel = new MyDrawPanel();
        button = new JButton("Restart");
        button.addActionListener(this);
        panel.add(button);
        frame.add(panel);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);

    }

    private Timer timer;

    public void actionPerformed(ActionEvent e) {
        if (timer != null) {
            return;
        }
        timer = new Timer(100, new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent evt) {
                if (panel.update()) {
                    timer.stop();
                    timer = null;
                }
            }
        });
        timer.start();
    }

    class MyDrawPanel extends JPanel {

        private int xPosy = 0;
        private int yPosy = 0;

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(300, 300);
        }

        public boolean update() {
            xPosy++;
            yPosy++;
            repaint();

            return xPosy > getWidth() || yPosy > getHeight();
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);            
            g.fillOval(xPosy, yPosy, 30, 30);
            g.setColor(Color.BLACK);
        }
    }
}

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