iOS: layer background color not showing when view background color is clear color

Question

I have two sibling views: a gray label and a green button, button is underneath. For some reason, I need to set label.backgroundColor to clear color and set label.layer.backgroundColor to grey. And button color is green. I expect to see grey on screen (because label is on top of button). But all I see is green (color of button). Why?

EDIT: relevant code

// in my custom cell
-(void)awakeFromNib
{
    [super awakeFromNib];

    // customize label
    _label.layer.cornerRadius = 5;
    _label.layer.backgroundColor = [UIColor grayColor].CGColor;
    _label.backgroundColor = [UIColor clearColor];
    _label.layer.masksToBounds = NO;


    // customize button        
    // show shadow and rounded corner at the same time

    _button.backgroundColor = [UIColor clearColor];
    _button.layer.backgroundColor = [UIColor greenColor].CGColor;
    _button.layer.masksToBounds = NO;
    _button.layer.cornerRadius = 10.0f;

    self.layer.masksToBounds = NO;
    self.layer.cornerRadius = 10.0f;
    self.layer.shadowOpacity = 0.5f;
    self.layer.shadowPath = [UIBezierPath bezierPathWithRoundedRect:_button.bounds cornerRadius:10.0f].CGPath;
    self.layer.shadowOffset = CGSizeMake(0.0f, 4.0f);
    self.layer.shadowRadius = 2.0f;

}

"For some reason" What reason? If we know the rationale behind your decisions, we might be able to help you better. — duci9y, Mar 24 '13 at 11:40
Because I need to round the corners of label while keeping `label.layer.masksToBounds = NO` (otherwise scrolling is stuttered severely). Thus I think the only option is to set `label.layer.backgroundColor` instead of `label.backgroundColor` — Philip007, Mar 24 '13 at 11:46
I was just having trouble with this issue, and for me it was a very simple fix. I forgot to set the View's isOpaque value to false. In IB this defaults to true, and if it is true the phone won't draw the view behind this view leaving a black background. — TMin, Apr 20 '18 at 10:02

Philip007 · Accepted Answer · 2013-03-26T13:08:18.677

16

Finally I found the solution: simply reverse the order of this two lines:

// both set to clear color eventually
_label.layer.backgroundColor = [UIColor grayColor].CGColor;
_label.backgroundColor = [UIColor clearColor];

to this:

// both set to gray eventually
_label.backgroundColor = [UIColor clearColor];
_label.layer.backgroundColor = [UIColor grayColor].CGColor;

The reason is that for UILabel, (not UIView though, more on it later) setting its background color will set it's layer's background color to nil. But if we set label background color first, and set layer background color later, then both go their own ways, then we would see label background color on screen.

But for UIView, it's a totally different story: view background color and its layer's background color is the same thing. Therefore whichever set last will prevail.

However, I cannot find anything about above observation in documentation. Hope someone could step in and help.

edited Mar 26 '13 at 13:08

answered Mar 24 '13 at 15:03

Philip007

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UIViews are layer backed, view and layer aren't two things but one. The view doesn't draw itself, only the layer gets drawn however you configure the view and/or the layer. – Pascal Mar 24 '13 at 15:48
Pascal, I used to think just like that. But like I experimented in this very post, at least for background color, view and it's layer behave wildly different. – Philip007 Mar 24 '13 at 15:53
For labels, seemingly, but not for UIView IIRC. UIView draws its layer in `- (void)drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx` just how you configure it or its layer. – Pascal Mar 24 '13 at 16:04
3

OK, but how about UILabel? – Philip007 Mar 24 '13 at 17:07

score 0 · Answer 2 · answered Apr 20 '18 at 10:03

0

Don't forget to set the view's isOpaque value to false. This defaults to true in IB.

answered Apr 20 '18 at 10:03

TMin

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iOS: layer background color not showing when view background color is clear color

2 Answers2