的paintComponent的多个电话（）

问题描述

我有这两个类：

public class Pencil extends JComponent implements MouseListener, MouseMotionListener{
Plansa plansa;
Graphics g;
public Pencil(Plansa newCanvas){
    this.plansa = newCanvas;
    this.plansa.setFlagShape(false);
}
@Override
public void mouseDragged(MouseEvent arg0) {
    plansa.setMouseDragged(arg0);
    this.plansa.setFlagShape(false);
    plansa.paintComponent(plansa.getGraphics());
}

@Override
public void mouseClicked(MouseEvent e) {
}

@Override
public void mousePressed(MouseEvent arg0) {
    plansa.setMousePressed(arg0);
}

@Override
public void mouseReleased(MouseEvent arg0) {
    // TODO Auto-generated method stub
    plansa.setMouseReleased(arg0);
    this.plansa.setFlagShape(true);
    plansa.paintComponent(plansa.getGraphics());

}

@Override
public void mouseEntered(MouseEvent e) {
}

@Override
public void mouseExited(MouseEvent e) {
}

@Override
public void mouseMoved(MouseEvent e) {
}

}

而这其中：

public class Plansa extends JPanel{
Image image;
Pencil pencil;
 //...
 void init(){
    this.setShape("freeLine");
    this.setColor(Color.BLACK);
    this.size=1;
    this.type="round";
    this.fill=false;
    this.setBackground(Color.WHITE);
    pencil = new Pencil(this);
    addMouseListener(pencil);
    addMouseMotionListener(pencil);
    flagPaint = true;
    flagShape = false;
}
public Plansa(){
    this.setSize(800, 600);
    init();
}

//...

       @Override
    public void paintComponent(Graphics g) {
    g.setColor(currentColor);
    Graphics2D g2d = (Graphics2D) g;
    g2d.setStroke(setBrush(size,type));
    super.paintComponent(g);
    switch(shape){
        default: break;
        case "freeLine":{
            g.drawLine(xDragged, yDragged, xCurrent, yCurrent);
            break;
        }
            case "rectangle":{
                if(flagShape == true){
            g.drawRect(xPressed, yPressed, Math.max(xCurrent-xPressed,xPressed-xCurrent), Math.max(yCurrent-yPressed,yPressed-yCurrent));
            if(fill == true) g.fillRect(xPressed, yPressed, Math.max(xCurrent-xPressed,xPressed-xCurrent), Math.max(yCurrent-yPressed,yPressed-yCurrent));
                }
            break;
        }
        case "circle":{
            if(flagShape == true){
            int radius = (int)Math.sqrt(Math.max(xCurrent-xPressed,xPressed-xCurrent)*Math.max(xCurrent-xPressed,xPressed-xCurrent)+Math.max(yCurrent-yPressed,yPressed-yCurrent)*Math.max(yCurrent-yPressed,yPressed-yCurrent));
            g.drawOval(xPressed, yPressed, radius, radius);
            if(fill == true) g.fillOval(xPressed, yPressed, radius, radius);
            }
            break;
        }
        case "oval":{
            if(flagShape == true){
            g.drawOval(xPressed, yPressed, Math.max(xCurrent-xPressed,xPressed-xCurrent), Math.max(yCurrent-yPressed,yPressed-yCurrent));
            if(fill == true) g.fillOval(xPressed, yPressed, Math.max(xCurrent-xPressed,xPressed-xCurrent), Math.max(yCurrent-yPressed,yPressed-yCurrent));
            }
            break;
        }
        case "line":{
            if(flagShape == true){
            g.drawLine(xPressed, yPressed, xCurrent, yCurrent);
            }
            break;
        }
    }

}

 //...
}

我的问题是，每次我打电话的paintComponent（）方法，JPanel中清除，而且是唯一产品我刚绘制的之一。有没有什么办法避免这种情况？

My problem is that every time I call paintComponent() method, the JPanel clears and the only item that remains is the one I just drawn. Is there any way to avoid this?

推荐答案

一般逐行图纸更好的方法是使用的BufferedImage 作为画布，因为看到此处。

A better idea generally for progressive drawings is to use a BufferedImage as the canvas, as seen here.

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