drawRect introduce

最新推荐文章于 2025-12-04 14:59:40 发布

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本文详细介绍了UIView中的drawRect:方法，该方法用于在指定区域内绘制视图内容。子类如果需要绘制自己的视图，则需要覆盖此方法。默认情况下，该方法不执行任何操作。文章还解释了坐标转换的应用及如何获取当前绘图上下文。

drawRect:
Draws the receiver’s image within the passed-in rectangle.
- (void)drawRect:(CGRect)rect
Parameters
rect
A rectangle defining the area to restrict drawing to.
Discussion
Subclasses override this method if they actually draw their views. Subclasses need not override this method if the subclass is a container for other views. The default implementation does nothing. If your custom view is a direct UIView subclass, you do not need to call the implementation of super. Note that it is the responsibility of each subclass to totally fill rect if its superclass’s implementation actually draws and opaqueis YES.
When this method is invoked, the receiver can assume the coordinate transformations of its frame and bounds rectangles have been applied; all it needs to do is invoke rendering client functions. Use the UIGraphicsGetCurrentContext function to get the current graphics context for drawing that also has the coordinate origin in the upper-left corner. Do not retain the graphics context since it can change between calls to thedrawRect: method.
Availability
Available in iPhone OS 2.0 and later.
See Also
– setNeedsDisplay
– setNeedsDisplayInRect:
@property contentMode
Declared In
UIView.h