没有在JPanel中显示添加到另一个JPanel的图形 [英] Not showing graphics in JPanel which is added to another JPanel

问题描述

将具有图形的 JPanel 添加到 JFrame 时，它运行正常。但是当我尝试添加一个 JPanel ，其中我添加了另一个带有图形的 JPanel ，它没有显示在的JFrame 。请参阅下面的代码

When adding a JPanel that has graphics to a JFrame, it's working fine. But when I try to add a JPanel in which I have added another JPanel with graphics, its not showing in the JFrame. Please see code below

package sample;

import java.awt.Graphics;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class Main extends JFrame{
    public static void main(String[] args) {
        new Main();
    }

    public Main(){
        setTitle("Sample");
        setVisible(true);
        setSize(500,500);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        add(new SamplePanel2());
    }
}

class SamplePanel2 extends JPanel{
    public SamplePanel2(){
        add(new JButton("Hi"));
        add(new SamplePanel());
    }
}
class SamplePanel extends JPanel {
    public SamplePanel(){
    }

    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawString("HHHHHHHHHHHH", 100, 100);
    }
}

推荐答案

请观察 Main 类的构造函数，使其成为habbit，遵循此示例中所示的顺序。首先将组件添加到 JFrame 然后只进行调用，如 pack（），setSize（）或setVisible（...），而不是在那之前。

Please do watch the constructor of the Main Class, make this your habbit to follow the sequence as shown in this example. First add components to the JFrame then only make calls like pack(), setSize() or setVisible(...), not before that.

总是让它成为你的习惯，每当你覆盖 paintcomponent（）方法时，覆盖 getPreferredSize（）方法。

Always make it your habbit, that whenever you override paintcomponent() method, override getPreferredSize() method as well.

并始终调用 pack（）/ EDT中的setVisible（...） - 事件调度线程。有关该主题的更多详细信息，请阅读 Swing中的并发。

And always put calls like pack()/setVisible(...) inside the EDT - Event Dispatch Thread. Please read Concurrency in Swing, for more detail on the topic.

import java.awt.Dimension;
import java.awt.Graphics;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class Main extends JFrame{
    public static void main(String[] args) {
        new Main();
    }

    public Main(){
        setTitle("Sample");        
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setContentPane(new SamplePanel2());
        pack();        
        setVisible(true);
    }
}

class SamplePanel2 extends JPanel{
    public SamplePanel2(){
        add(new JButton("Hi"));
        add(new SamplePanel());
    }
}
class SamplePanel extends JPanel {
    public SamplePanel(){
    }

    @Override
    public Dimension getPreferredSize()
    {
        return (new Dimension(300, 300));
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawString("HHHHHHHHHHHH", 100, 100);
    }
}

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