java - 调整窗口大小时 Canvas 会被清除

Question

我正在尝试制作一个绘画程序，但我的 Canvas 遇到了这个问题，每次我调整大小或最大化包含它的窗口时，它都会清除。我真的不知道问题出在哪里，paint()和repaint()方法在canvas类中没有被重写，并且我没有使用任何适配器来调整窗口大小。任何帮助将不胜感激。

代码如下:

public class Plansa extends Canvas{
Image image;
Pencil pencil;
public Plansa(){
    this.setSize(800, 600);
    this.setBackground(Color.white);
    pencil = new Pencil(this);
    addMouseListener(pencil);
    addMouseMotionListener(pencil);
}
public Plansa(int width, int height){
    this.setBounds(0, 0, width, height);
    this.setBackground(Color.white);
    pencil = new Pencil(this);
    addMouseListener(pencil);
    addMouseMotionListener(pencil);
}
public Plansa(Image imag) {
    this.setBackground(Color.white);
    this.setSize(imag.getWidth(this), imag.getHeight(this));
    image = imag;
    this.image = imag;
    this.repaint();
    pencil = new Pencil(this);
    addMouseListener(pencil);
    addMouseMotionListener(pencil);  

        }


public Dimension getPreferredSize() { 
    if(image==null)  
        return new Dimension( 800, 600 );  
    int w = image.getWidth( this );  
    int h = image.getHeight( this );  
    return new Dimension( w, h );  
 }

}



public class Fereastra extends JFrame{
private Plansa plansa;

public Fereastra () {
    super( "***Painter***" ) ;
    Dimension dimension = Toolkit.getDefaultToolkit().getScreenSize();
    int x = (int) ((dimension.getWidth() - this.getWidth())/2);
    int y = (int) ((dimension.getHeight() - this.getHeight())/2);
    this.setLocation(0, 0);
    this.setSize(dimension);
    plansa = new Plansa(this.getWidth(), this.getHeight());

    //...

    setDefaultCloseOperation(EXIT_ON_CLOSE);

    add (plansa, BorderLayout.CENTER ) ;
    pack();
}

}

Answer 1

听起来就像您使用 getGraphics 进行绘图 - 答案是不要这样做。而是重写 paintComponent 方法:

public class Canvas extends JPanel {

    public void paintComponent(Graphics g) {
        super.paintComponent(g) // paints background

        /* do your drawings here */

    }

}

_{如果这没有帮助，请花点时间发布您的绘图代码。}