Frame of your overlay view has zero size:
UIView *btnView = [[UIView alloc] initWithFrame:CGRectZero];
Change it like this and you will see it:
UIView *btnView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 1024, 1024];
Update:
Also enable clipsToBounds
flag: btnView.clipsToBounds = YES;