Java Swing GlassPane拖动性能

Question

我试图使用GlassPane在我的Swing应用程序中进行可视化拖放，但遇到了拖拽图像滞后于鼠标指针的问题。我该如何解决这个问题？我的GlassPane代码如下。谢谢!

package dragui;

import java.awt.*;
import javax.swing.*;
import java.awt.event.MouseEvent;
import javax.swing.event.MouseInputAdapter;

public class GlassPane extends JComponent {
    private int x=0, y=0, k=25,z=1;
    private boolean showDot;
    private MouseInputAdapter mia = new MouseInputAdapter(){

        @Override
        public void mouseDragged(MouseEvent me) {
            setPos(me.getX(), me.getY());
        }

        @Override
        public void mousePressed(MouseEvent me) {
            setShow(true);
            setPos(me.getX(), me.getY());   
        }

        @Override
        public void mouseReleased(MouseEvent me){
            setShow(false);
            setVisible(false);
        }
    };

    public void setShow(boolean b){ this.showDot = b; }

    public void paint(Graphics g) {
        if (showDot) {
            g.setColor(new Color(0.0f, 0.25f, 1.0f));
            g.fillOval(x - k, y - k, 2*k, 2*k);
        }
    }

    public void setPos(int x, int y) {
        int tmpX = this.x, tmpY = this.y; 
        this.x = x; this.y = y;
        repaint(tmpX - k , tmpY-k, 2*k+5, 2*k+5);
        repaint(this.x-k, this.y-k, 2*k+5, 2*k+5);        
    }

    public GlassPane() {
        addMouseListener(mia); 
        addMouseMotionListener(mia);
        setOpaque(false);
    }
}

Answer 1

根据Javadoc的说法

如果一个子类只是想要专门化UI (外观)委托的

方法，那么它就应该覆盖paintComponent。

这是因为paint(...)实际上将绘制工作委托给了三个受保护的方法：paintComponent、paintBorder和paintChildren。也就是说，试着用下面的代码替换paint(...)

@Override
protected void paintComponent(Graphics g) {
    if (showDot) {
        Graphics gCopy = g.create();

        gCopy.setColor(new Color(0.0f, 0.25f, 1.0f));
        gCopy.fillOval(x - k, y - k, 2*k, 2*k);

        gCopy.dispose();
    }
}

Answer 2

也许你不应该在每次重新绘制时创建一个new Color(0.0f, 0.25f, 1.0f)。

对我来说，这场表演相当不错。

public class Example {
    static public void main( String[] s ) {
        EventQueue.invokeLater( new Runnable() {
            public void run() {
                JFrame frame = new JFrame();
                frame.setBounds( 50, 50, 600, 600 );
                frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
                frame.setGlassPane( new JComponent() {
                    {
                        MouseInputAdapter mia = new MouseInputAdapter(){
                            public void mouseDragged(MouseEvent me) {
                                setPos(me.getX(), me.getY());
                            }
                            public void mousePressed(MouseEvent me) {
                                setShow(true);
                                setPos(me.getX(), me.getY());   
                            }
                            public void mouseReleased(MouseEvent me){
                                setShow(false);
                                setVisible(false);
                            }
                        };
                        addMouseListener(mia); 
                        addMouseMotionListener(mia);
                        setOpaque(false);
                    }
                    private int x=0, y=0, k=25,z=1;
                    private boolean showDot;
                    public void setShow(boolean b){ this.showDot = b; }
                    private Color color = new Color(0.0f, 0.25f, 1.0f);
                    public void paintComponent(Graphics g) {
                        if (showDot) {
                            g.setColor(color);
                            g.fillOval(x - k, y - k, 2*k, 2*k);
                        }
                    }
                    public void setPos(int x, int y) {
                        int tmpX = this.x, tmpY = this.y; 
                        this.x = x; this.y = y;
                        repaint(tmpX - k , tmpY-k, 2*k+5, 2*k+5);
                        repaint(this.x-k, this.y-k, 2*k+5, 2*k+5);        
                    }
                } );
                frame.getGlassPane().setVisible( true );
                frame.setVisible( true );
            }
        });
    }
}