UIButton never responds
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Here's my view hierarchy: parentView (UIView) has a UIImageView as its subview which in turn has a UIButton as its subview. 

    left = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"left.png"]];
    left.userInteractionEnabled = YES;
    [parentView addSubview:left];
    
    back = [UIButton buttonWithType:UIButtonTypeCustom];
    [back setImage:[UIImage imageNamed:@"Arrow-left.png"] forState:UIControlStateNormal];
    [back addTarget:self action:@selector(back:) forControlEvents:UIControlEventTouchUpInside];
    back.showsTouchWhenHighlighted = YES;
    [left addSubview:back];

Everything shows up properly but the button does not respond to touches. It does respond if I move its frame out of the UIImageView's frame to somewhere else and set it as a subView to the parentView (UIView). But here's the thing. Even if I set to parentView's subView the button does not respond if it is within the UIImageView's frame area. The userInteractionEnabled property has been already set to YES for the image view. Any idea what's going on?
    
