Java 如何将JPanel的内容复制到BuffereImage

我从一个列表（this.docList）中有两个BuffereImage。在我的paintComponent方法中，我将它们绘制到JPanel，同时在'this.createdImage'上绘制它们

@Override
protected void paintComponent(Graphics g){
    super.paintComponent(g);
    this.createdImage = newBufferedImage(this.getWidth(),this.getHeight(), BufferedImage.TYPE_INT_ARGB); Graphics g2 = this.createdImage.getGraphics();
    if (controlWhichImage == 1){
        for(BufferedImage eachImage : docList){
            g2.drawImage(eachImage,0,inty,imageWidth,imageHeight,null);
            g.drawImage(eachImage, 0,inty,imageWidth,imageHeight,null);
            intx += eachImage.getWidth();
            inty += eachImage.getHeight() * zoomAdd;
            }

        if (intx >= this.getWidth() || inty >= this.getHeight()){
            inty = 0;
        }

我的问题是，当我使用createdImage时，我得到的只是一个空白面板

if (controlWhichImage == 2){
     g.drawImage(this.createdImage,this.getWidth(),this.getHeight(),null);
}

---

每次调用

paintComponent

时，您都会创建一个

BufferedImage

的新实例，如果

controlwhichichimage

是

1

它会将图像绘制到

BufferedImage

，如果它是

2

它绘制的，那么就什么都没有了

基本上你的代码基本上是这样运行的

Override
protected void paintComponent(Graphics g){
    super.paintComponent(g);
    this.createdImage = newBufferedImage(this.getWidth(),this.getHeight(), BufferedImage.TYPE_INT_ARGB); 
    Graphics g2 = this.createdImage.getGraphics();
    if (controlWhichImage == 1){
        for(BufferedImage eachImage : docList){
            g2.drawImage(eachImage,0,inty,imageWidth,imageHeight,null);
            g.drawImage(eachImage, 0,inty,imageWidth,imageHeight,null);
            intx += eachImage.getWidth();
            inty += eachImage.getHeight() * zoomAdd;
        }

        if (intx >= this.getWidth() || inty >= this.getHeight()){
            inty = 0;
        }
    } else if (controlWhichImage == 2){
         g.drawImage(this.createdImage,this.getWidth(),this.getHeight(),null);
    }

当

controlWhichImage

为

1

Override
protected void paintComponent(Graphics g){
    super.paintComponent(g);
    if (controlWhichImage == 1){
        this.createdImage = newBufferedImage(this.getWidth(),this.getHeight(), BufferedImage.TYPE_INT_ARGB); 
        Graphics g2 = this.createdImage.getGraphics();
        for(BufferedImage eachImage : docList){
            g2.drawImage(eachImage,0,inty,imageWidth,imageHeight,this);
            g.drawImage(eachImage, 0,inty,imageWidth,imageHeight,this);
            intx += eachImage.getWidth();
            inty += eachImage.getHeight() * zoomAdd;
        }

        if (intx >= this.getWidth() || inty >= this.getHeight()){
            inty = 0;
        }
        g2.dispose(); // This is kind of important...
    } else if (controlWhichImage == 2){
         g.drawImage(this.createdImage,this.getWidth(),this.getHeight(),this);
    }

或者当

createdImage

为空时

Override
protected void paintComponent(Graphics g){
    super.paintComponent(g);
    if (createdImage == null){
        this.createdImage = newBufferedImage(this.getWidth(),this.getHeight(), BufferedImage.TYPE_INT_ARGB); 
        Graphics g2 = this.createdImage.getGraphics();
        for(BufferedImage eachImage : docList){
            g2.drawImage(eachImage,0,inty,imageWidth,imageHeight,this);
            intx += eachImage.getWidth();
            inty += eachImage.getHeight() * zoomAdd;
        }

        if (intx >= this.getWidth() || inty >= this.getHeight()){
            inty = 0;
        }
        g2.dispose(); // This is kind of important...
    }
    g.drawImage(this.createdImage,this.getWidth(),this.getHeight(),this);

---

每次调用

paintComponent

时，您都会创建一个

BufferedImage

的新实例，如果

controlwhichichimage

是

1

它会将图像绘制到

BufferedImage

，如果它是

2

它绘制的，那么就什么都没有了

基本上你的代码基本上是这样运行的

Override
protected void paintComponent(Graphics g){
    super.paintComponent(g);
    this.createdImage = newBufferedImage(this.getWidth(),this.getHeight(), BufferedImage.TYPE_INT_ARGB); 
    Graphics g2 = this.createdImage.getGraphics();
    if (controlWhichImage == 1){
        for(BufferedImage eachImage : docList){
            g2.drawImage(eachImage,0,inty,imageWidth,imageHeight,null);
            g.drawImage(eachImage, 0,inty,imageWidth,imageHeight,null);
            intx += eachImage.getWidth();
            inty += eachImage.getHeight() * zoomAdd;
        }

        if (intx >= this.getWidth() || inty >= this.getHeight()){
            inty = 0;
        }
    } else if (controlWhichImage == 2){
         g.drawImage(this.createdImage,this.getWidth(),this.getHeight(),null);
    }

当

controlWhichImage

为

1

Override
protected void paintComponent(Graphics g){
    super.paintComponent(g);
    if (controlWhichImage == 1){
        this.createdImage = newBufferedImage(this.getWidth(),this.getHeight(), BufferedImage.TYPE_INT_ARGB); 
        Graphics g2 = this.createdImage.getGraphics();
        for(BufferedImage eachImage : docList){
            g2.drawImage(eachImage,0,inty,imageWidth,imageHeight,this);
            g.drawImage(eachImage, 0,inty,imageWidth,imageHeight,this);
            intx += eachImage.getWidth();
            inty += eachImage.getHeight() * zoomAdd;
        }

        if (intx >= this.getWidth() || inty >= this.getHeight()){
            inty = 0;
        }
        g2.dispose(); // This is kind of important...
    } else if (controlWhichImage == 2){
         g.drawImage(this.createdImage,this.getWidth(),this.getHeight(),this);
    }

或者当

createdImage

为空时

Override
protected void paintComponent(Graphics g){
    super.paintComponent(g);
    if (createdImage == null){
        this.createdImage = newBufferedImage(this.getWidth(),this.getHeight(), BufferedImage.TYPE_INT_ARGB); 
        Graphics g2 = this.createdImage.getGraphics();
        for(BufferedImage eachImage : docList){
            g2.drawImage(eachImage,0,inty,imageWidth,imageHeight,this);
            intx += eachImage.getWidth();
            inty += eachImage.getHeight() * zoomAdd;
        }

        if (intx >= this.getWidth() || inty >= this.getHeight()){
            inty = 0;
        }
        g2.dispose(); // This is kind of important...
    }
    g.drawImage(this.createdImage,this.getWidth(),this.getHeight(),this);

---

好的，我已将其更改为：if（createdImage==null）{this.createdImage=new buffereImage（this.getWidth（），this.getHeight（），buffereImage.TYPE_INT_ARGB）；}，但在2上它仍然为空。但是谢谢你的回复，好吧，因为你选择不提供一个能证明你的问题的答案，其他所有的事情都是纯粹的猜测。对不起，我试着让它尽可能简单。这并不是说我不想提供一个可运行的示例，而是说如何使其保持简单。好的，我已经将其更改为：if（createdImage==null）{this.createdImage=new buffereImage（this.getWidth（），this.getHeight（），buffereImage.TYPE_INT_ARGB）}，但在2上它仍然是空的。但是谢谢你的回复，好吧，因为你选择不提供一个能证明你的问题的答案，其他所有的事情都是纯粹的猜测。对不起，我试着让它尽可能简单。这并不是说我不想提供一个可运行的示例，而是如何让它保持简单。不要执行昂贵的操作，比如在paint方法中创建BuffereImage。每秒可以调用多次paintComponent（和所有绘制方法）！重复。不要执行昂贵的操作，如在绘制方法内创建BuffereImage。每秒可以调用多次paintComponent（和所有绘制方法）！副本。