java 清除JPanel
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Clearing JPanel
提问by Adrian D'Urso
I am making a program in which there is a square that changes its x and y positions when a key is pressed. The square moves but the the old square is still there. How do I remove/clear everything from a panel before I repaint it? Calling removeAllhad no effect.
我正在制作一个程序，其中有一个正方形，当按下某个键时，它会改变其 x 和 y 位置。广场移动了，但旧广场还在。在重新粉刷面板之前，如何从面板上移除/清除所有内容？调用removeAll没有效果。
采纳答案by user268396
Presumably your code includes custom paintComponent()logic. The key thing to observe is what does your panel look like when you do notoverride paintComponent()? An empty (or cleared) panel:
大概您的代码包含自定义paintComponent()逻辑。要观察的关键是当您不覆盖时您的面板是什么样子的paintComponent()？一个空的（或清除的）面板：
Thus the solution is to invoke the paintComponent()method of the parent type on the panel, before executing your custom paintComponent()logic:
因此，解决方案是paintComponent()在执行自定义paintComponent()逻辑之前调用面板上父类型的方法：
public class CustomPanel extends JPanel {
@Override
public void paintComponent(Graphics g) {
super.paintComponent(g); // first draw a clear/empty panel
// then draw using your custom logic.
}
}
回答by Mike K.
I think this should work.
我认为这应该有效。
g.clearRect (0, 0, panel.getWidth(), panel.getHeight());
Also, you could keep the old location of the square and just clear that rather than clear the whole background.
此外，您可以保留广场的旧位置并清除它而不是清除整个背景。
