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我正在尝试创建一个简单的绘图程序，但每次调用 myDrawingPanel2.repaint() 时，该程序都会简单地擦除已绘制的旧点，并在新位置用一个点替换它。我在 Mac OS X 10.8 上使用最新版本的 Java JDK(u15) 和最新版本的 Netbeans 运行它。我希望程序继续绘制点而不擦除前一个点。

这是我的申请表的代码：

private void myDrawingPanel2MouseClicked(java.awt.event.MouseEvent evt) {                                             
    myDrawingPanel2.setxC(evt.getX());
    myDrawingPanel2.setyC(evt.getY());

    myDrawingPanel2.repaint();
}                                            

private void myDrawingPanel2MouseDragged(java.awt.event.MouseEvent evt) {                                             
    myDrawingPanel2.setxC(evt.getX());
    myDrawingPanel2.setyC(evt.getY());

    myDrawingPanel2.repaint();
}                                            

private void upActionPerformed(java.awt.event.ActionEvent evt) {                                   
    myDrawingPanel2.setyC(myDrawingPanel2.getyC()-5);

    myDrawingPanel2.repaint();
}                                  

private void downActionPerformed(java.awt.event.ActionEvent evt) {                                     
    myDrawingPanel2.setyC(myDrawingPanel2.getyC()+5);

    myDrawingPanel2.repaint();
}                                    

private void leftActionPerformed(java.awt.event.ActionEvent evt) {                                     
    myDrawingPanel2.setxC(myDrawingPanel2.getxC()-5);

    myDrawingPanel2.repaint();
}                                    

private void rightActionPerformed(java.awt.event.ActionEvent evt) {                                      
    myDrawingPanel2.setxC(myDrawingPanel2.getxC()+5);

    myDrawingPanel2.repaint();
}                                     

private void upKeyPressed(java.awt.event.KeyEvent evt) {                              
    if(evt.getKeyCode() == 38) {
        myDrawingPanel2.setyC(myDrawingPanel2.getyC()-5);
    }
    if(evt.getKeyCode() == 40) {
        myDrawingPanel2.setyC(myDrawingPanel2.getyC()+5);
    }
    if(evt.getKeyCode() == 39) {
        myDrawingPanel2.setxC(myDrawingPanel2.getxC()+5);
    }
    if(evt.getKeyCode() == 37) {
        myDrawingPanel2.setxC(myDrawingPanel2.getxC()-5);
    }
    myDrawingPanel2.repaint();
}                             

private void leftKeyPressed(java.awt.event.KeyEvent evt) {                                
    if(evt.getKeyCode() == 38) {
        myDrawingPanel2.setyC(myDrawingPanel2.getyC()-5);
    }
    if(evt.getKeyCode() == 40) {
        myDrawingPanel2.setyC(myDrawingPanel2.getyC()+5);
    }
    if(evt.getKeyCode() == 39) {
        myDrawingPanel2.setxC(myDrawingPanel2.getxC()+5);
    }
    if(evt.getKeyCode() == 37) {
        myDrawingPanel2.setxC(myDrawingPanel2.getxC()-5);
    }
    myDrawingPanel2.repaint();
}                               

private void downKeyPressed(java.awt.event.KeyEvent evt) {                                
    if(evt.getKeyCode() == 38) {
        myDrawingPanel2.setyC(myDrawingPanel2.getyC()-5);
    }
    if(evt.getKeyCode() == 40) {
        myDrawingPanel2.setyC(myDrawingPanel2.getyC()+5);
    }
    if(evt.getKeyCode() == 39) {
        myDrawingPanel2.setxC(myDrawingPanel2.getxC()+5);
    }
    if(evt.getKeyCode() == 37) {
        myDrawingPanel2.setxC(myDrawingPanel2.getxC()-5);
    }
    myDrawingPanel2.repaint();
}                               

private void rightKeyPressed(java.awt.event.KeyEvent evt) {                                 
    if(evt.getKeyCode() == 38) {
        myDrawingPanel2.setyC(myDrawingPanel2.getyC()-5);
    }
    if(evt.getKeyCode() == 40) {
        myDrawingPanel2.setyC(myDrawingPanel2.getyC()+5);
    }
    if(evt.getKeyCode() == 39) {
        myDrawingPanel2.setxC(myDrawingPanel2.getxC()+5);
    }
    if(evt.getKeyCode() == 37) {
        myDrawingPanel2.setxC(myDrawingPanel2.getxC()-5);
    }
    myDrawingPanel2.repaint();
}

这是我的 JPanel 的代码：

package drawingdemo;

import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JPanel;


public class MyDrawingPanel extends JPanel{

int xC = 150;
int yC = 100;
int diameter = 25;

public int getxC() {
    return xC;
}

public void setxC(int xC) {
    this.xC = xC;
}

public int getyC() {
    return yC;
}

public void setyC(int yC) {
    this.yC = yC;
}

public int getDiameter() {
    return diameter;
}

public void setDiameter(int diameter) {
    this.diameter = diameter;
}

@Override
public void paintComponent(Graphics g){

    //super.paintComponent(g);

    g.setColor(Color.RED);
    g.fillOval(xC - (diameter/2), yC - (diameter/2), diameter, diameter);

}

}
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1 回答 1

1

该程序执行您告诉它执行的操作。paintComponent用于绘制整个组件，您的实现绘制一个点。如果您希望您的组件显示多个点，您可以提供一个paintComponent绘制多个点的实现。这意味着您必须记住所有点的位置。

有一些技巧可以迫使 Swing 不清除背景，但这些技巧会很麻烦，因为您没有实现正确的语义。可见的屏幕状态可能随时丢失，例如当另一个窗口与您的窗口重叠时，或者如果用户最小化并恢复窗口或显示设置更改。因此，您必须提供一个paintComponent无论如何都能够恢复整个预期显示内容的实现。

于 2013-10-01T21:20:53.053 回答