I would like to know the difference between:
On the screenshot I have made two UIViews with two black (alpha = 1.0) UILabels on top of each:
Assume a macro _RGB is defined before:
#define _RGB(r,g,b,a) [UIColor colorWithRed:r/255.0 green:g/255.0 blue:b/255.0 alpha:a]
and then here is the code::
[_view1 setBackgroundColor:_RGB(255, 0, 0, 1)];
[_view1 setAlpha:0.5];
[_view2 setBackgroundColor:_RGB(255, 0, 0, 0.5)];
[_view2 setAlpha:1];
[_view3 setBackgroundColor:_RGB(255, 0, 0, 1)];
[_view3 setAlpha:1];
I can see only one difference visually: Changing view's own alpha instead of bg color's, affects the subviews as well. But other than that is there any difference in functionality that I should consider? (eg. On animations, layers, etc.)
The difference is:
So in your examples:
_view1
(alpha <1 on view): alpha is also applied to the subview UILabel_view2
(alpha <1 on background color): subview UILabel is nicely opaque_view3
(defualt alpha 1 on both): well, we all see :-) background color and label are both opaqueExample usage of both:
Left image: You have a semi-transparent black overlay which has a subview UIImageView
containing a white checkmark icon and you usually want the icon to be fully opaque (non-transparent). So you set just the background color black with alpha <1 (0.75f in the example).
In opposing to:
Right image: You have have a semi-transparent black overlay which has a subview UIImageView
containing a white pattern image (the pattern is opaque white, no alpha). And you want the pattern in overlay to be also semi-transparent. You then would set background color to black with alpha 1 (opaque) and alpha <1 to the whole view.
As you can see, icon on left image is fully opaque, but on a right, you can see also through a stars pattern.