java - 创建新的 Bufferstrategy 时出现非法状态异常

Question

当我试图弄清楚如何使用缓冲策略时，总体上只是改进我编写代码和清理东西的方式。当我运行以下代码时，在“createBufferStrategy(3)”

时出现错误

    package Game1Test;

import java.awt.Canvas;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.image.BufferStrategy;
import java.io.IOException;

import javax.swing.*;

public class Base extends Canvas implements Runnable{

    private static final long serialVersionUID = 1L;
    private boolean running = false;
    int ticks = 0;

    public Base(JFrame f) {
        setSize(f.getWidth(),f.getHeight());
        start();
    }

    public void start(){
        running = true;
        new Thread(this).start();
    }
    public void stop(){

    }
    public void run(){
        while(running){
            ticks++;
            System.out.println(ticks);
            render();

                try {
                    Thread.sleep(2);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
        }
    }
    public void render(){
        BufferStrategy bs = getBufferStrategy();
        Graphics g;
        if(bs == null){
            createBufferStrategy(3);
            requestFocus();
            return;
        }
        bs.show();
    }



}

然后在 Base 中添加:

package Game1Test;

import java.awt.*;

import javax.swing.JFrame;

public class Screen extends JFrame{

    public final int GAME_WIDTH = 400;
    public final int GAME_HEIGHT = 400;
    public Dimension gameDim = new Dimension(GAME_WIDTH,GAME_HEIGHT);
    final String gameName = "Test";

    public Screen(){
        setSize(gameDim);
        setTitle(gameName);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setResizable(false);
        setLayout(new GridLayout());
        setVisible(true);
        setLocationRelativeTo(null);
    }
    public static void main(String[] args){
        Screen s = new Screen();
        s.add(new Base(s));
    }
}

我收到以下错误:

Exception in thread "Thread-2" java.lang.IllegalStateException: Component must have a valid peer
    at java.awt.Component$FlipBufferStrategy.createBuffers(Unknown Source)
    at java.awt.Component$FlipBufferStrategy.<init>(Unknown Source)
    at java.awt.Component$FlipSubRegionBufferStrategy.<init>(Unknown Source)
    at java.awt.Component.createBufferStrategy(Unknown Source)
    at java.awt.Canvas.createBufferStrategy(Unknown Source)
    at java.awt.Component.createBufferStrategy(Unknown Source)
    at java.awt.Canvas.createBufferStrategy(Unknown Source)
    at Game1Test.Base.render(Base.java:46)
    at Game1Test.Base.run(Base.java:33)
    at java.lang.Thread.run(Unknown Source)

谁能告诉我为什么会这样？也许是解决这个问题的方法？

谢谢

Answer 1

看看 API ，如果组件不可显示，则会抛出此异常。在这种情况下，即 Canvas.peer 为 null 时。查看 peer 字段会发现

The peer is set when the Component is added to a container that also is a peer

由于您是从组件的构造函数启动更新线程，因此可以在将组件添加到另一个容器之前调用 render，这意味着 peer 是 null，然后将抛出 IllegalStateException。