Make intersection transparent using multiple subviews - iphone

Question

Please check below image. i have added scrollview in "BLACK" color and added subview in "GREY" color. now i want to make subview transparent which is define as "WHITE" color.
Please refer the below code. Let me know how to make button transparent with particular frame or let me know if you have any alternative for that.
self.scrollView = [[UIScrollView alloc] initWithFrame:CGRectMake(0.0, 40.0, self.frame.size.width, 300.0)];
self.scrollView.contentSize = CGSizeMake(self.bounds.size.width,ViewHeight);
self.scrollView.autoresizingMask=UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
self.scrollView.delegate = self;
self.scrollView.backgroundColor =[UIColor blackColor];
[self.view addSubview:self.scrollView
UIButton *butApp = [UIButton buttonWithType:UIButtonTypeCustom];
[butApp setFrame:CGRectMake(x, y , w, h)];
[butApp setBackgroundColor:[UIColor greyColor]];
[self.scrollView addSubview:butApp];
UIButton* gapButton = [UIButton buttonWithType:UIButtonTypeCustom];
[gapButton setFrame:CGRectMake(x+3, y+10, w-6, 10)];
[gapButton setBackgroundColor:[UIColor whiteColor]];
[self.scrollView addSubview:gapButton];
Instead of this gapButton i need transparent portion in grey color so user can see black color in that portion.

Answer 1

Try this, I suggested it in comments. Other answer requires subclassing UIButton, which you suggested was not ideal in your situation.
UIButton *butApp = [UIButton buttonWithType:UIButtonTypeCustom];
[butApp setFrame:CGRectMake(x, y , w, h)];
//[butApp setBackgroundColor:[UIColor greyColor]]; //replace this...
[butApp setBackgroundImage:[UIImage imageNamed:#"greyWithHoleInCenter.png"]
forState:UIControlStateNormal]; //...with this
[self.scrollView addSubview:butApp];
I created a crude .png file to represent the kind of backgroundImage you might be looking for. Note that the center is clear, not white. Therefore, it should show whatever image is behind it:

Answer 2

Ok. Funny question. In my opinion you have to override drawRect: + drawInContext: methods by subclassing UIView class.
You also need to set the container view (the gray view) + button bg to clearColor
-(void)drawRect:(CGRect)r
{
// Let this method blank will cause drawLayer:InContext to be called
}
-(void)drawLayer:(CALayer*)layer inContext:(CGContextRef)context
{
// Fill the bg with gray
CGContextSetFillColorWithColor(context, [UIColor grayColor].CGColor);
CGContextFillRect(context, self.bounds);
// I clear the subview frames
for (UIView * v in [self subviews]) // I do it for all subviews
{
CGContextSetBlendMode(context, kCGBlendModeClear);
CGContextFillRect(context, v.frame);
}
}