我正在尝试在 Java 中渲染一个蓝色方块，但出现 IllegalStateException 错误有人能帮我吗？

编程问答 2022-05-30

问题描述

我试图在 Java 中将一个蓝色方块渲染到屏幕上，但蓝色方块没有显示出来，而且我得到了一个 IllegalStateException。

创建窗口类

package Graphics;

import java.awt.Dimension;

import javax.swing.JFrame;

public class CreateWindow {
    
    
    public CreateWindow(int width,int height,String title) {
        Dimension d = new Dimension();
        JFrame frame;
        
        
            d.width =  width;
            d.height = height;
            
            frame = new JFrame();
            
            frame.setPreferredSize(d);
            frame.setMinimumSize(d);
            frame.setMaximumSize(d);
            
            frame.setResizable(false);
            frame.setTitle(title);
            frame.setDefaultCloSEOperation(JFrame.EXIT_ON_CLOSE);
            frame.setLocationRelativeto(null);
            frame.setVisible(true);
            
            new BufferedImageOperation();
        
    }
    
    
    public void deleteWindow() {}
    
    
    public static void main(String[] args) {
        new CreateWindow(500,500,"POOP");
    }
}

BufferedImageOperation 类

package Graphics;

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

public class BufferedImageOperation extends Canvas {
        
    private static final long serialVersionUID = 1L;
    public BufferedImageOperation() {
        render();
    }
    public  void render() {
        BufferStrategy bs = getBufferStrategy();
        if(bs == null) {
            createBufferStrategy(3);
            return; 
        }
        
        Graphics g = bs.getDrawGraphics();
        
        g.setColor(Color.BLUE);
        g.drawRect(0,32,32);
        g.dispose();
        bs.show();
    }
}

控制台是这样说的：

Exception in thread "main" java.lang.IllegalStateException: Component must have a valid peer
    at java.desktop/java.awt.Component$FlipBufferStrategy.createBuffers(Component.java:4106)
    at java.desktop/java.awt.Component$FlipBufferStrategy.<init>(Component.java:4080)
    at java.desktop/java.awt.Component$FlipSubRegionBufferStrategy.<init>(Component.java:4608)
    at java.desktop/java.awt.Component.createBufferStrategy(Component.java:3943)
    at java.desktop/java.awt.Canvas.createBufferStrategy(Canvas.java:195)
    at java.desktop/java.awt.Component.createBufferStrategy(Component.java:3867)
    at java.desktop/java.awt.Canvas.createBufferStrategy(Canvas.java:170)
    at Graphics.BufferedImageOperation.render(BufferedImageOperation.java:17)
    at Graphics.BufferedImageOperation.<init>(BufferedImageOperation.java:12)
    at Graphics.CreateWindow.<init>(CreateWindow.java:30)
    at Graphics.CreateWindow.main(CreateWindow.java:39)

解决方法

了解异常在哪里抛出很重要，但我怀疑 BufferedImageOperation 不可见，未添加到任何（可见）组件中，
例如：frame.add(new BufferedImageOperation());。

编辑：检查 createBufferStrategy():

的文档

throws IllegalStateException - 如果组件不可显示

和isDisplayable()：

当一个组件被添加到一个可显示的包含层次结构或者当它的包含层次结构被设置为可显示时，它就会被设置为可显示的。当其祖先窗口被打包或可见时，包含层次结构将变为可显示。

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