重绘在JAVA小程序，而不会丢失previous内容 [英] Repaint Applets in JAVA without losing previous contents

问题描述

是否有可能重新画一个小程序，而不会失去它的previous内容是什么？我只是试图让一个程序，它允许用户绘制线条，矩形等使用鼠标。我已经使用了重新绘制方法，但它不守previously绘制的线条/矩形等。

下面是片段：

 公共无效鼠标pressed（的MouseEvent E）{X1 = e.getX（）; Y1 = e.getY（）;}
公共无效的mouseDragged（的MouseEvent E）
{
    X2 = e.getX（）;
    Y2 = e.getY（）;
    重绘（）;
    showStatus（开始点：+ X1 +，+ Y1 +终点：+ 2 +，+ Y2）;
}
公共无效漆（图形G）
{
    //g.drawLine(x1,y1,x2,y2）;
    g.drawRect（X1，Y1，X2-X1，Y2-Y1）;}
 

解决方案

有两种可能的解决方案：

1. 使用图形通过从该对象获取的getGraphics（）绘制到一个BufferedImage，然后绘制的BufferedImage在JPanel中的的paintComponent（图形摹）方法。或


2. 创建一个的ArrayList＆LT;点＆GT; 将鼠标点到列表，然后在JPanel的的paintComponent（图形G）方法，遍历一个for循环的清单，绘制所有点，或有时更好 - 连接相邻点线

其他重要建议：

• 请确保您使用的Swing库（JApplet的，JPanel中），而不是AWT（小程序，面板，帆布）。


• 你最好避免小程序，如果在所有可能的。


• 请不要在paint方法绘制，而是一个JPanel的的paintComponent（图形G）方法。


• 请不要忘了调用超类的方法，第一件事就是在你的的paintComponent（图形G）方法重写。

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.

Here is the snippet:

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);

}

解决方案

Two possible solutions:

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.

Other important suggestions:

• 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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