java JFrame 图形 [英] java JFrame graphics

问题描述

我在 JFrame 构造函数中有以下简单代码

I have the following simple code in a JFrame constructor

    super(name);
    setBounds(0,0,1100,750);
    setLayout(null);


    setVisible(true);

    g = this.getGraphics();
    int[] x =new int[]{65,  122,  77,  20, };
    int[] y =new int[]{226,  258, 341,  310};
    g.setColor(Color.RED);  
    g.drawPolygon (x, y, x.length);
    System.out.println(g);

我在控制台上得到的输出为:

I get the output on console as:

sun.java2d.SunGraphics2D[font=java.awt.Font[family=Dialog,name=Dialog,style=plain,size=12],color=java.awt.Color[r=255,g=0,b=0]]

sun.java2d.SunGraphics2D[font=java.awt.Font[family=Dialog,name=Dialog,style=plain,size=12],color=java.awt.Color[r=255,g=0,b=0]]

但在 JFrame 上没有绘制红色多边形，只有空白的 JFrame.

But no red polygon drawn on JFrame but just the blank JFrame.

为什么??

推荐答案

• 不要覆盖JFrame

  而是将带有覆盖的 paintComponent(Graphics g) 的 custom JPanel 添加到 JFrame

  Rather add custom JPanel with overridden paintComponent(Graphics g) to JFrame

  不要使用 Null/AbsoluteLayout 使用合适的 LayoutManager

  Dont use Null/AbsoluteLayout use an appropriate LayoutManager

  不要在 JFrame 实例上调用 setBounds(..)(不是不允许，但在这个应用程序中看不到它是相关的)

  Dont call setBounds(..) on JFrame instance (not that its not allowed but cant see it being relevant in this application)

  不要忘记使用 EDT 来创建并更改 GUI 组件:

  Dont forget to use EDT for creating and changing GUI components:

  javax.swing.SwingUtilities.invokeLater(new Runnable() {
              @Override
             public void run() {
                  Test test = new Test();
             }
  });
  

然后你会做这样的事情:

you would then do something like this:

public class Test {

    /**
     * Default constructor for Test.class
     */
    public Test() {
        initComponents();
    }

    public static void main(String[] args) {

        /**
         * Create GUI and components on Event-Dispatch-Thread
         */
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                Test test = new Test();
            }
        });
    }

    /**
     * Initialize GUI and components (including ActionListeners etc)
     */
    private void initComponents() {
        JFrame jFrame = new JFrame();
        jFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        jFrame.add(new MyPanel());

        //pack frame (size JFrame to match preferred sizes of added components and set visible
        jFrame.pack();
        jFrame.setVisible(true);
    }
}

class MyPanel extends JPanel {

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        int[] x = new int[]{65, 122, 77, 20};
        int[] y = new int[]{226, 258, 341, 310};
        g.setColor(Color.RED);
        g.drawPolygon(x, y, x.length);
    }

    //so our panel is the corerct size when pack() is called on Jframe
    @Override
    public Dimension getPreferredSize() {
        return new Dimension(400, 400);
    }
}

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