//---------------------
//Parent view
[self.view setBackgroundColor:[[UIColor clearColor] colorWithAlphaComponent:0.5]];
//Subview
[sview setBackgroundColor:[[UIColor clearColor] colorWithAlphaComponent:1.0]];
//--------------------
UIView *view.backgroundColor=[[UIColor blackColor] colorWithAlphaComponent:.6];
It's not the same as:
UIView *view.backgroundColor=[UIColor blackColor];
view.alpha=.6;