在 JAVA 中重新绘制小程序而不会丢失以前的内容 [英] Repaint Applets in JAVA without losing previous contents

问题描述

是否可以重新绘制小程序而不丢失其先前的内容?我只是想制作一个程序，允许用户使用鼠标绘制线条、矩形等.我使用了重绘方法，但它不保留以前绘制的线条/矩形等.

Is it possible to re-paint an applet without losing its previous contents? I was just trying to make a program which allows users to draw lines, Rectangle etc. using mouse. I have used the repaint method but it does not keep the previously drawn lines/rectangles etc.

这是片段:

public void mousePressed(MouseEvent e){x1=e.getX();y1=e.getY();}
public void mouseDragged(MouseEvent e)
{
    x2=e.getX();
    y2=e.getY();
    repaint();
    showStatus("Start Point: "+x1+", "+y1+"         End Point: "+x2+", "+y2);
}
public void paint(Graphics g)
{
    //g.drawLine(x1,y1,x2,y2);
    g.drawRect(x1, y1, x2-x1, y2-y1);

}

推荐答案

两种可能的解决方案:

1. 使用通过getGraphics() 获取的Graphics 对象绘制到BufferedImage，然后在JPanel 的paintComponent(Graphics g) 方法中绘制BufferedImage.或者
2. 创建一个ArrayList，将鼠标指向List，然后在JPanel的paintComponent(Graphics g)方法中，用for循环遍历List循环，绘制所有点，或者有时更好 - 连接连续点的线.

1. Draw to a BufferedImage using the Graphics object obtained from it via getGraphics(), and then draw the BufferedImage in your JPanel's paintComponent(Graphics g) method. Or
2. Create an ArrayList<Point> place your mouse points into the List, and then in the JPanel's paintComponent(Graphics g) method, iterate through the List with a for loop, drawing all the points, or sometimes better -- lines that connect the contiguous points.

其他重要建议:

• 确保您使用的是 Swing 库(JApplet、JPanel)，而不是 AWT(Applet、Panel、Canvas).
• 如果可能，您最好避免使用小程序.
• 不要在paint方法中绘制，而是在JPanel的paintComponent(Graphics g)方法中绘制.
• 不要忘记在您的 paintComponent(Graphics g) 方法覆盖中首先调用 super 的方法.

• Be sure that you're using the Swing library (JApplet, JPanel), not AWT (Applet, Panel, Canvas).
• You're better off avoiding applets if at all possible.
• Don't draw in a paint method but rather a JPanel's paintComponent(Graphics g) method.
• Don't forget to call the super's method first thing in your paintComponent(Graphics g) method override.

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