Subview appears underneath superviews layer.border

问题:

I have a UIView in which I define it's border in the following manner:

self.layer.borderColor = [UIColor blackColor].CGColor;
self.layer.borderWidth = 3;

I attach a subview to this UIView, and when I move the subview over the border, it goes underneath it. Is this the intended behavior? Is there anyway to make the subview go on top of it?

回答1:

According to the Apple specification: It is composited above the receiver’s contents and sublayers.

So, the border will always be above of all your subviews, even if you bring your subview to the front and so on.

So I make a background view to fake the border.

E.g.:

UIView *backgroundView = [[UIView alloc] initWithFrame:CGRectMake(100, 100, 200, 200)];
backgroundView.backgroundColor = [UIColor blackColor];
backgroundView.clipsToBounds = NO;

UIView *bView = [[UIView alloc] initWithFrame:CGRectInset(backgroundView.bounds, 3, 3)];
bView.backgroundColor = [UIColor redColor];

UIView *cView = [[UIView alloc] initWithFrame:CGRectMake(-50, -50, 100, 100)];
cView.backgroundColor = [UIColor yellowColor];
[bView addSubview:cView];

[backgroundView addSubview:bView];

[self.window addSubview:backgroundView];

and the effect:

回答2:

Did you try setting the superview's 'clipsToBounds' property to YES? This is set to NO by default for performance reasons, but setting it to yes might give you the effect you are looking for.

回答3:

Depending on your view structure, it might be easier to add the subview to the parent of your main view. It can then overlap the main view and will overlay the border as you requested.