Setting alpha on UIView sets the alpha on its subviews which should not happen

I think this is a bug in the documentation. You should file it at bugreport.apple.com.

Everything I can see after a bit of quick research suggests what you are seeing is how it always has behaved, and my own testing shows it too.

The alpha of a view is applied to all subviews.

Perhaps all you need is [[UIColor blackColor] colorWithAlphaComponent:0.5] but if not you will need to make the view a sibling instead of a child.

Don't set the alpha directly on the parent view. Instead of it use the below line of code which will apply transparency to parentview without affecting its child views.

[parentView setBackgroundColor:[[UIColor clearColor] colorWithAlphaComponent:0.5]];

In swift

view.backgroundColor = UIColor.whiteColor().colorWithAlphaComponent(0.5)

UPDATED FOR SWIFT 3

view.backgroundColor = UIColor.white.withAlphaComponent(0.5)

Set Opacity of the background color instead of alpha will not affect its child views.

1. select view.
2. go to attribute inspector than background color
3. click on "others"
4. set opacity to 30%

Or you can set by programmetically

var customView:UIView = UIView()
customView.layer.opacity = 0.3

Thats it. Happy Coding!!!