UIView重写drawRect导致视图不遵守masksToBounds [英] UIView overriding drawRect causes view not to obey masksToBounds

问题描述

我试图在自定义视图中覆盖UIView的 drawRect：方法。但是，我的视图的边界半径定义为：

I am trying to override the drawRect: method of UIView in my custom view. However, my view has a border radius defined as:

    sub = [[[NSBundle mainBundle] loadNibNamed:@"ProfileView" owner:self options:nil] objectAtIndex:0];
    [self addSubview:sub];
    [sub setUserInteractionEnabled:YES];
    [self setUserInteractionEnabled:YES];
    CALayer *layer = sub.layer;
    layer.masksToBounds = YES;
    layer.borderWidth = 5.0;
    layer.borderColor = [UIColor whiteColor].CGColor;
    layer.cornerRadius = 30.0;

这完美无缺，并在我的视图周围放置了一个带边框半径的漂亮边框（不介意背面的对角线/直白线，它们与此视图无关）：

This works perfectly and places a nice border with a border radius around my view (don't mind the diagonal/straight white lines at the back, they have nothing to do with this view):

然而，当我尝试覆盖 drawRect：在我看来，我可以看到黑色背景没有掩盖到边界。我不做任何（目前），这是我的代码：

However, when I try to override the drawRect: method in my view, I can see a black background not masking to bounds. I don't do anything (currently), here is my code:

-(void)drawRect:(CGRect)rect{
    [super drawRect:rect];
}

结果如下：

我'除了绘制方法之外什么都没改变。如何在保持视图遵循角半径蒙版的同时覆盖绘制方法？这是iOS中的错误还是我错过了什么？

I've changed nothing but the draw method. How can I override the draw method while keeping my view obey the corner radius mask? Is this a bug in iOS or am I missing something?

推荐答案

我不知道完整的答案，但我知道UIView的 drawLayer：inContext：的实现方式不同，具体取决于你是否实现了 drawRect：。也许掩盖/限制边界是其中一种不同的方式。

I don't know the full answer, but I do know that UIView's implementation of drawLayer:inContext: works differently depending on whether you have implemented drawRect: or not. Perhaps masking/clipping to bounds is one of those things it does differently.

您可以尝试通过多种方式解决问题：

You can try solving your issue a number of ways:

• 让你的背景透明：

• make your background transparent:

    layer.backgroundColor = [UIColor clearColor].CGColor;

将自己剪辑到自定义 drawRect：：

- (void)drawRect:(CGRect)rect {
    [[UIBezierPath bezierPathWithRoundedRect:rect cornerRadius:30.0] addClip];
    [image drawInRect:rect];  // or whatever
}

明确划出角落：

carve out the corners explicitly:

CGContextBeginPath(c);
CGContextAddArc(c, r, r, r, M_PI, 3*M_PI_2, 0);
CGContextAddLineToPoint(c, 0, 0);
CGContextClosePath(c);
CGContextClip(c);
[[UIColor grayColor] setFill];
UIRectFill(rect);

我偷了这个伟大的最后2条建议来自WWDC 2010的演示： iPhone OS上的高级性能优化（视频列在< a href =https://developer.apple.com/videos/wwdc/2010/\"rel =nofollow>这个索引页面 - 烦人的，没有直接的链接。）

I stole those last 2 suggestions from this great presentation from WWDC 2010: Advanced Performance Optimization on iPhone OS (video listed at this index page -- annoyingly, no direct link).

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