为什么我的形状和图像在我的面板上消失？ [英] Why do my shapes and images disappear on my panel?

问题描述

我使用 paintComponent 方法在面板上绘制图形。但是，每次我最小化框架或调整大小时，它们都会消失。不知道要添加到我的代码中。

  public class ShapePanel extends JPanel implements ActionListener，MouseListener {
 
 int a，b，c，d; 
 Graphics2D g2D; 
 private Rectangle2D rect = new Rectangle2D（a，b，c-a，d-b）; 
 
 public ShapePanel（）{
 
 addMouseListener（this）; 
 setLayout（new GridLayout（））; 
} 
 
 public void paintComponent（Graphics g）{
 
 g2D =（Graphics2D）g; 
 g2D.draw（rect）; 
 repaint（）; 
 
 
 
 
 //获取坐标的方法：MousePressed，MouseReleased 
  

解决方案不要在 paintComponent 下调用 repaint（） / code>方法。另外，请在 paintComponent 方法中执行 super.paintComponent（g）。

更新：您的代码有很多编译错误。然而，请看下面的变更列表：

• new Rectangle2D（a，b，c，d ）应该是新的 Rectangle2D.Float（10，10，100，100）; 或者无论如何，a，b，c和d应该有一些值，否则它们都是零，所以没有矩形


• 在定义和构造函数中命名该类


• 实现 mouseClicked ， mouseEntered 和 mouseExited


• 从 actionPerformed 中删除​​ g2D.draw（），并且不要保留对 g2D 。

如果您需要，我有完整的代码可用。

I have used the paintComponent method to draw shapes on my panel. However, every time I minimize the frame or resize it, they disappear. Not sure what to add to my code.

   public class ShapePanel extends JPanel implements ActionListener, MouseListener{

    int a,b,c,d;
    Graphics2D g2D;
    private Rectangle2D rect = new Rectangle2D(a,b,c-a,d-b);

    public ShapePanel(){

    addMouseListener(this);
    setLayout(new GridLayout());
}

    public void paintComponent(Graphics g) {

    g2D = (Graphics2D) g;
    g2D.draw(rect);
    repaint();

}


   //get methods for coordinates: MousePressed, MouseReleased

解决方案

Don't call repaint() under the paintComponent method. Also, do super.paintComponent(g) the first thing in your paintComponent method.

Update: your code has a lot of compile errors. However, please see below a list of things to change:

• new Rectangle2D(a, b, c, d) should be new Rectangle2D.Float(10, 10, 100, 100); or anyway, a, b, c and d should have some values, otherwise they are all zero, so no rectangle
• name the class the same both in definition and in constructor
• implement mouseClicked, mouseEntered and mouseExited
• remove g2D.draw() from actionPerformed and don't keep a reference to g2D in the class.

I have the full code that is working if you need it.

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