java - 如何将 JPanel 的内容复制到 BufferedImage

Question

我有一个列表(this.docList)中的两个 BufferedImage。在我的 PaintComponent 方法中，我将它们绘制到 JPanel，同时将它们绘制到“this.createdImage”上。

@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);
}

Answer 1

每次调用paintComponent时，都会创建一个BufferedImage的新实例，如果controlWhichImage是1它将图像绘制到 BufferedImage，如果它是 2，则绘制，但什么也不绘制。

基本上你的代码的运行方式基本上就像......

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 时，您应该只创建 createdImaeg 的实例

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);