java - 如何将paintComponent()添加到JPanel

Question

我有 2 个类(class)，Class2 和 Class4。我希望使用 p4.add(c2o) 和 f.add(p4) 方法将 Class2 中的绘画从 Class4 添加到 Class4 中的 JPanel 上。添加 GUI 没有任何问题，但我就是无法添加图形。

4级:

import java.awt.BorderLayout;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;

public class Class4 {


    public void mainMethod(int event){
        JFrame f = new JFrame("Love Test");
        if(event == 0){

            f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            f.setSize(500,200);
            f.setLayout(null);

            JPanel p = new JPanel(new BorderLayout());
            p.setBounds(150, 0, 350, 75);
            Class3 c3o = new Class3();
            p.add(c3o);
            f.add(p);

            JPanel p2 = new JPanel();
            Class7 c7o = new Class7();
            p2.add(c7o);
            p2.setBounds(0, 75, 500, 40);
            f.add(p2);

            JPanel p3 = new JPanel();
            p3.setBounds(0, 0, 150, 75);
            Class5 c5o = new Class5();
            p3.add(c5o);
            f.add(p3);

            f.setVisible(true);

        }

        if(event == 5){

            JPanel p4 = new JPanel();
            Class2 c2o = new Class2();
            p4.add(c2o);
            p4.setBounds(0,115,500,55);
            f.add(p4);
        }

    }


}

2级:

import javax.swing.JOptionPane;
import javax.swing.JPanel;

import java.util.Random;
import java.awt.*;



public class Class2 extends JPanel{

    public void paint(Graphics g){
        super.paint(g);
        this.setBackground(Color.WHITE);
        g.setColor(new Color(0,0,0));
        String str = "";
        String str2 = "";
        Random rlove = new Random();
        int love = rlove.nextInt(101);
        Class3 c3o = new Class3();
        str = c3o.boy.getText() + " and " + c3o.girl.getText() + "'s amount of love is " + love + "%.";
        if(love >= 0 && love < 10){         
            str2 = "Stop thinking about that person anymore!";
        }
        if(love >= 10 && love < 20){
            str2 = "1/100 percent chance...";
        }
        if(love >= 20 && love < 30){
            str2 = "Little hope...";
        }
        if(love >= 30 && love < 40){
            str2 = "Not even a kiss, stop talking about French kisses! (wise words of Rubesh)";
        }
        if(love >= 40 && love < 50){
            str2 = "Near passing";
        }
        if(love >= 50 && love < 60){
            str2 = "Just Pass";
        }
        if(love >= 60 && love < 70){
            str2 = "Some effort needed.";
        }
        if(love >= 70 && love < 80){
            str2 = "Grade A. A good chance.";
        }
        if(love >= 80 && love < 90){
            str2 = "Good pair. Very good relationship!";
        }
        if(love >= 90 && love < 100){
            str2 = "Perfect pair. Lost for words.";
        }
        if(love == 100){
            str2 = "OH MY GOD!!!!!";
        }
        g.drawString(str,10,10);
        g.drawString(str2,10,30);
    }


}

如何将paintComponent添加到JPanel p4？谢谢!

Answer 1

1. 不要使用JPanel#paint，建议使用JPanel#paintComponent，查看Performing Custom Painting
2. 使用适当的布局管理器。您遇到的问题来自两个问题。首先，您的面板没有首选尺寸。重写 Class2 的 getPreferredSize 方法并返回布局管理器的适当大小。

...

JPanel p4 = new JPanel(); // Default layout manager is FlowLayout
Class2 c2o = new Class2();
// c2o has not size (0x0 by default)...
p4.add(c2o);
p4.setBounds(0,115,500,55);
f.add(p4);