下面是JDK文档对这个方法的说明,看不明白,麻烦解释一下:
另外,如果不调用超类的实现,[color=#FF0000]则必须遵守不透明属性,也就是如果此组件是不透明的,则必须以透明的颜色完全填充背景。如果不遵守不透明属性,则很可能看到可视化的人为内容。 [/color]
super.paintComponent和组件的背景有什么联系?
另外,如果不调用超类的实现,[color=#FF0000]则必须遵守不透明属性,也就是如果此组件是不透明的,则必须以透明的颜色完全填充背景。如果不遵守不透明属性,则很可能看到可视化的人为内容。 [/color]
super.paintComponent和组件的背景有什么联系?
* Calls the UI delegate's paint method, if the UI delegate
* is non-<code>null</code>. We pass the delegate a copy of the
* <code>Graphics</code> object to protect the rest of the
* paint code from irrevocable changes
* (for example, <code>Graphics.translate</code>).
* <p>
* If you override this in a subclass you should not make permanent
* changes to the passed in <code>Graphics</code>. For example, you
* should not alter the clip <code>Rectangle</code> or modify the
* transform. If you need to do these operations you may find it
* easier to create a new <code>Graphics</code> from the passed in
* <code>Graphics</code> and manipulate it. Further, if you do not
* invoker super's implementation you must honor the opaque property,
* that is
* if this component is opaque, you must completely fill in the background
* in a non-opaque color. If you do not honor the opaque property you
* will likely see visual artifacts.
* <p>
* The passed in <code>Graphics</code> object might
* have a transform other than the identify transform
* installed on it. In this case, you might get
* unexpected results if you cumulatively apply
* another transform.
*
* @param g the <code>Graphics</code> object to protect
* @see #paint
* @see ComponentUI
*/
protected void paintComponent(Graphics g) {
if (ui != null) {
Graphics scratchGraphics = (g == null) ? null : g.create();
try {
ui.update(scratchGraphics, this);
}
finally {
scratchGraphics.dispose();
}
}
} /**
* Notifies this UI delegate that it's time to paint the specified
* component. This method is invoked by <code>JComponent</code>
* when the specified component is being painted.
* By default this method will fill the specified component with
* its background color (if its <code>opaque</code> property is
* <code>true</code>) and then immediately call <code>paint</code>.
* In general this method need not be overridden by subclasses;
* all look-and-feel rendering code should reside in the <code>paint</code>
* method.
*
* @param g the <code>Graphics</code> context in which to paint
* @param c the component being painted;
* this argument is often ignored,
* but might be used if the UI object is stateless
* and shared by multiple components
*
* @see #paint
* @see javax.swing.JComponent#paintComponent
*/
public void update(Graphics g, JComponent c) {
if (c.isOpaque()) {
g.setColor(c.getBackground());
g.fillRect(0, 0, c.getWidth(),c.getHeight());
}
paint(g, c);
}