在 UIImage 上绘制透明圆圈 - iPhone SDK

Drawing a transparent circle on top of a UIImage - iPhone SDK(在 UIImage 上绘制透明圆圈 - iPhone SDK)

问题描述

我在尝试找出如何在我的 UIImageView 中的 UIImage 上绘制透明圆圈时遇到了很多麻烦.Google-ing 给了我线索，但我仍然找不到一个可行的例子.

I am having a lot of trouble trying to find out how to draw a transparent circle on top of a UIImage within my UIImageView. Google-ing gives me clues, but I still can't find a working example.

是否有任何人都知道的例子可以证明这一点?

Are there any examples that anyone knows of that demonstrate this?

推荐答案

最简单的方法就是创建一个半透明的方形UIView，然后将其图层的cornerRadius设置为其宽度/高度的一半.比如:

Easiest way is simply to create a semi-transparent square UIView, then set the cornerRadius of its layer to be half of its width/height. Something like:

UIView *squareView = [[UIView alloc] initWithFrame:CGRectMake(0,0,100,100)];
squareView.alpha = 0.5;
squareView.layer.cornerRadius = 50;
...
[squareView release];

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