如何在JFrame的paint（）函数之外绘制图形 [英] How to draw graphics outside of the paint() function in a JFrame

问题描述

我希望能够在 JFrame 上绘制 Image s，但是只要我想要（不在 JFrame.paint 方法。

对于我正在开发的项目，我有一个 class Bullseye extends BufferedImage ，并试图将它放到 JFrame ：

  class DrawingFrame extends JFrame {
 public void drawImage（Image img，int x，int y）{
 getGraphics（）。drawImage（img，x，y，null ）; 
 repaint（）; 
} 
} 
 
 class Main {
 public static void main（String [] args）{
 DrawingFrame frame = new DrawingFrame（）; 
 Bullseye bullseye = new Bullseye（20,20）; //宽度，高度
 
 //稍后
 frame.setVisible（true）; 
 frame.drawImage（bullseye，10,20）; 
 frame.drawImage（bullseye，20,20）; 
 frame.drawImage（bullseye，30,20）; 
} 
} 
  

然而， ws up。经过一番研究，显然这是行不通的，因为当我 repaint（）时，图形 。

我该怎么做？这甚至是正确的方法吗？

解决方案

在Java中绘制屏幕（几乎）总是在paint（）中完成。你需要的类是：

  class DrawingFrame extends JFrame {
 
 private Image bullseye = new牛眼（20,20）; //宽度，高度
 
 
 public void paint（Graphics g）{
 g.drawImage（bullseye，10,20）; 
 g.drawImage（bullseye，20,20）; 
 g.drawImage（bullseye，30,20）; 
 
 
 
 $ b class Main {
 public static void main（String [] args）{
 DrawingFrame frame = new DrawingFrame（ ）; 
 
 //稍后
 frame.setVisible（true）; 
 
 
 
 
 $ b如果你需要开启bullseyes的绘图在特定的时间，在DrawingFrame对象上创建一个标志，并在需要时设置它。您需要在设置标志时调用repaint（）。
 
I would like to be able to paint Images onto a JFrame, but whenever I want (not in the JFrame.paint method.

For the project I am working on, I have a class Bullseye extends BufferedImage, and am trying to put it onto a JFrame:
class DrawingFrame extends JFrame {
    public void drawImage(Image img, int x, int y) {
        getGraphics().drawImage(img,x,y,null);
        repaint();
    }
}

class Main {
    public static void main(String[] args) {
        DrawingFrame frame = new DrawingFrame();
        Bullseye bullseye = new Bullseye(20,20); //width,height

        // later
        frame.setVisible(true);
        frame.drawImage(bullseye,10,20);
        frame.drawImage(bullseye,20,20);
        frame.drawImage(bullseye,30,20);
    }
}
However, nothing shows up. After some research, apparently this doesn't work because the changes to the graphics object get cleared when I repaint().

How can I do this? Is this even the right approach?
解决方案
Drawing to the screen in Java is (almost) always done in paint(). What you need for your class is:
class DrawingFrame extends JFrame {

    private Image bullseye = new Bullseye(20,20); //width,height


    public void paint(Graphics g) {
        g.drawImage(bullseye,10,20);
        g.drawImage(bullseye,20,20);
        g.drawImage(bullseye,30,20);
    }

}

class Main {
    public static void main(String[] args) {
        DrawingFrame frame = new DrawingFrame();

        // later
        frame.setVisible(true);
    }
}
If you need to turn on the drawing of bullseyes at a specific time, create a flag on the DrawingFrame object, and set it when you need them. You will need to call repaint() when the flag is set.

                        
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