Question

我想创建一条线，并在2秒后打破另一条线，依此类推。如果我绘制一条线并用Thread.sleep（）暂停程序执行并再次在paintComponent（）方法中绘制一条线，那么首先程序停止2秒然后同时绘制两条线。如何克服这个问题？

Answer 1

这是真正的共同要求和问题。您应首先查看Concurrency in Swing和How to use Swing Timers，了解有关如何解决基本问题的一些基本信息。

您还应该查看Painting in AWT and Swing和Performing Custom Painting，了解有关绘画如何在Swing中工作的更多信息

您想要关注的核心设计选择是：

不要阻止事件调度线程，这将阻止它绘制任何内容或响应新事件
不要在EDT上下文之外更新用户界面
绘画应该绘画状态。它不应该专注于尽可能做出逻辑决策，相反，它应该依赖于一个或多个模型来为其提供绘制自己所需的信息

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Shape;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.geom.Line2D;
import java.util.ArrayList;
import java.util.List;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Test {

    public static void main(String[] args) {
        new Test();
    }

    public Test() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        private List<Shape> shapes;
        private int yPos = 0;

        public TestPane() {
            shapes = new ArrayList<>(25);

            Timer timer = new Timer(2000, new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    yPos += 10;
                    Line2D line = new Line2D.Double(0, yPos, getWidth(), yPos);
                    shapes.add(line);
                    repaint();
                }
            });
            timer.setInitialDelay(2000);
            timer.start();
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            for (Shape line : shapes) {
                g2d.draw(line);
            }
            g2d.dispose();
        }

    }

}

随着时间的推移逐个绘制形状而不是一次全部绘制形状

1 个答案: