java - 创建后绘制组件

Question

为了用 Java 创建我的第一个 2D 游戏，我想到使用 JFrame 的 getContentPane()，每 50 毫秒用新 View 更新一次。

JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
// ...
frame.setVisible(true);
// ...
Container area = frame.getContentPane();
Graphics pen = area.getGraphics();
pen.clearRect(0, 0, area.getWidth(), area.getHeight()); // Remove previous drawing
pen.drawString("Text", 50, 50);
// ...
area.repaint();

但是这不起作用；窗口没有改变。

Answer 1

正如 kiheru 已经说过的，使用 paintComponent(Graphics g) 进行自定义绘制。这是一个例子:

import javax.swing.*;

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

public class Example {

    int i = 0;

    public Example() {

        JFrame frame = new JFrame();

        frame.getContentPane().add(new DrawingPanel());

        frame.setSize(500, 500);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);

        ActionListener actionListener = new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {

                frame.getContentPane().repaint();

            }

        };

        Timer timer = new Timer(500, actionListener); //500 = Every 500 milliseconds
        timer.start();

    }

    class DrawingPanel extends JPanel {

        @Override
        public void paintComponent(Graphics g) {

            super.paintComponent(g); // Removes previous graphics

            Random r = new Random(); //Randomizer

            //Random x- and y-coordinates
            int x = r.nextInt(400);
            int y = r.nextInt(400);

            //Random rgb-values
            int red = r.nextInt(255); 
            int green = r.nextInt(255);
            int blue = r.nextInt(255);

            //Random width and height
            int width = r.nextInt(100);
            int height = r.nextInt(100);

            g.setColor(new Color(red, green, blue)); //Setting color of the graphics

            g.fillRect(x, y, width, height); //Filling a rectangle

        }

    }

    public static void main(String[] args) {

        new Example();

    }

}