java - 使用 getGraphics 进行闪烁绘画

Question

我正在做一个选择工具，我已经提供了这些解决方案，在第一个使用 JPanel getGraphics 方法中，我在鼠标拖动的地方绘制一个椭圆形，在第二个中，我重写 PaintComponent 方法来绘制椭圆形。

当我执行第一个方法时，拖动鼠标时会出现闪烁，并且绘图效果很差，而第二种方法则运行完美。为什么会发生这种情况？如果我在第一个解决方案中退出重绘，它会绘制椭圆形并且不会“删除”它们。

执行此类操作的最佳实践是什么？当我使用 getGraphics 绘图时，我是否遗漏了某些内容？

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;


public class TestGetGraphics extends JFrame {

    JPanel canvas;
    Painter painter;

    class Painter{
        void paint( Graphics2D g, Point p ){
            g.drawOval(p.x, p.y, 30, 30);
        }
    }

    public TestGetGraphics(){
        super();

        canvas = new JPanel();
        painter = new Painter();

        canvas.setPreferredSize( new Dimension(400, 400) );
        canvas.setBackground(Color.WHITE);

        canvas.addMouseMotionListener(new MouseAdapter() {
                public void mouseDragged(MouseEvent me){
                    painter.paint((Graphics2D) canvas.getGraphics(), me.getPoint());
                    canvas.repaint();
                }
        });

        add( canvas );

        setVisible(true);
        pack();
        setDefaultCloseOperation(EXIT_ON_CLOSE);
    }


    public static void main(String [] args){
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                new TestGetGraphics();
            }
        });
    }

}

这是paintComponent方法:

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;


public class TestPaintComponent extends JFrame  {
    JPanel canvas;
    Painter painter;

    class Painter{
        Point p;
        void paint( Graphics2D g ){
            if( p != null )
                g.drawOval(p.x, p.y, 30, 30);
        }

        void setPoint( Point p ){
            this.p = p;
        }
    }

    public TestPaintComponent(){
        super();

        canvas = new JPanel(){
            @Override
            public void paintComponent(Graphics g){
                super.paintComponent(g);
                painter.paint((Graphics2D) g);

            }

        };
        painter = new Painter();

        canvas.setPreferredSize( new Dimension(400, 400) );
        canvas.setBackground(Color.WHITE);

        canvas.addMouseMotionListener(new MouseAdapter() {
                public void mouseDragged(MouseEvent me){
                    painter.setPoint(me.getPoint());
                    canvas.repaint();
                }
        });

        add( canvas );

        setVisible(true);
        pack();
        setDefaultCloseOperation(EXIT_ON_CLOSE);
    }



    public static void main(String [] args){
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                new TestPaintComponent();
            }
        });
    }
}

Answer 1

不要在组件上调用 getGraphics()。相反，扩展组件并重写paintComponent()。更多信息请点击:http://docs.oracle.com/javase/tutorial/uiswing/painting/