Drawing rectangles on a JPanel

问题

I have a JScrollPane and on top of it I have a JPanel named 'panel1'. I want some rectangles to be drawn on this JPanel.

I have a class named DrawRectPanel which extends JPanel and does all the drawing stuff. The problem is that, I tried to draw the rectangles on panel1 by writing the following code :

panel1.add(new DrawRectPanel());

but nothing appeared on panel1 then I tried, just as a test to the class DrawRectPanel :

JFrame frame = new JFrame();
frame.setSize(1000, 500);
Container contentPane =    frame.getContentPane();
contentPane.add(new DrawRectPanel());
frame.show();

This worked, and produced the drawings but on a separate JFrame How can I draw the rectangles on panel1 ? Thanks in advance.

EDIT : code for DrawRectPanel

public class DrawRectPanel extends JPanel  {

    DrawRectPanel() {
        Dimension g = new Dimension(400,400);
        this.setPreferredSize(g);
        System.out.println("label 1");
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        System.out.println("label 2");
        g.setColor(Color.red);
        g.fillRect(20, 10, 80, 30);
    }
 }

only label 1 is printed on the screen

回答1:

still no idea,

for example

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import javax.swing.JComponent;
import javax.swing.JFrame;

public class CustomComponent extends JFrame {

    private static final long serialVersionUID = 1L;

    public CustomComponent() {
        setTitle("Custom Component Graphics2D");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public void display() {
        add(new CustomComponents());
        pack();
        // enforces the minimum size of both frame and component        
        setMinimumSize(getSize());
        setVisible(true);
    }

    public static void main(String[] args) {
        CustomComponent main = new CustomComponent();
        main.display();
    }
}

class CustomComponents extends JComponent {

    private static final long serialVersionUID = 1L;

    @Override
    public Dimension getMinimumSize() {
        return new Dimension(100, 100);
    }

    @Override
    public Dimension getPreferredSize() {
        return new Dimension(400, 300);
    }

    @Override
    public void paintComponent(Graphics g) {
        int margin = 10;
        Dimension dim = getSize();
        super.paintComponent(g);
        g.setColor(Color.red);
        g.fillRect(margin, margin, dim.width - margin * 2, dim.height - margin * 2);
    }
}

回答2:

instead of adding

contentPane.add(new DrawRectPanel());

you should do

contentPane.add(panel1);

Because you already have new DrawRectPanel in panel1. But in your code you are adding another instance of DrawRectPanel in contentPane. And never added panel1 in none of your container.

回答3:

to fix your problem, change "paintComponent" to "paint" when the window repaints automatically, it should work.

来源：https://stackoverflow.com/questions/7723591/drawing-rectangles-on-a-jpanel

标签

java

swing

jpanel

draw

graphics2d