问题是你画这样的JPanel:
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor (Color.CYAN);
g.fillRect(10,10,200,50);
g.setColor(Color.RED);
g.fillOval(50,50,50,50);
}
因此,如果创建JPanel时,它会绘制一个青色矩形和一个红色椭圆。 问题是,如果你想移动椭圆形,例如,你必须重新绘制整个面板!
如何制作2D物体并使其可移动和可更改而无需重新绘制整个面板?
答案 0 :(得分:2)
首先看看Painting in AWT and Swing和Performing Custom Painting,了解绘画过程。
你没有"有"如果您不想重新绘制整个面板,可以使用JPanel#repaint(int, int, int, int)
来指定要重新绘制的区域。
现在,请记住,如果您需要绘制用于包含椭圆的区域,然后绘制它现在所在的区域,这样可以确保先前的位置也会更新,否则您将获得重影。
/*
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package testball;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
public class TestBall {
public static void main(String[] args) {
new TestBall();
}
public TestBall() {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
ex.printStackTrace();
}
JFrame frame = new JFrame("Testing");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(new TestPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class TestPane extends JPanel {
private int x = 100 - 10;
private int y = 100 - 10;
private int delta = 4;
public TestPane() {
Timer timer = new Timer(40, new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
// Replace existing area...
repaint(x, y, 21, 21);
x += delta;
if (x + 20 >= getWidth()) {
x = getWidth() - 20;
delta *= -1;
} else if (x < 0) {
x = 0;
delta *= -1;
}
repaint(x, y, 21, 21);
}
});
timer.start();
}
@Override
public Dimension getPreferredSize() {
return new Dimension(200, 200);
}
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g.create();
g2d.setColor(Color.RED);
g2d.drawOval(x, y, 20, 20);
g2d.dispose();
}
}
}
答案 1 :(得分:1)
如果您的对象是新订单,则必须重新绘制。如果最小化和最大化窗口,默认情况下也会调用重绘。制作在移动时自动更新面板的2D对象的一种可能性是使用观察者模式: http://en.wikipedia.org/wiki/Observer_pattern