Cocoa Touch - Custom UIButton shape

Question

How can I make the touchable button area to be of the same shape of the image provided?
Say I have a custom button with a triangle image, how can I make sure that only t

Answer 1

OBShapedButton is a great Project for that

It works by subclassing UIButton and overriding -pointInside:withEvent:

@implementation OBShapedButton

// UIView uses this method in hitTest:withEvent: to determine which subview 
// should receive a touch event.
// If pointInside:withEvent: returns YES, then the subview’s hierarchy is 
// traversed; otherwise, its branch
// of the view hierarchy is ignored.
- (BOOL)pointInside:(CGPoint)point withEvent:(UIEvent *)event 
{
    // Return NO if even super returns NO (i.e. if point lies outside our bounds)
    BOOL superResult = [super pointInside:point withEvent:event];
    if (!superResult) {
        return superResult;
    }

    // We can't test the image's alpha channel if the button has no image. 
    // Fall back to super.
    UIImage *buttonImage = [self imageForState:UIControlStateNormal];
    if (buttonImage == nil) {
        return YES;
    }

    CGColorRef pixelColor = [[buttonImage colorAtPixel:point] CGColor];
    CGFloat alpha = CGColorGetAlpha(pixelColor);
    return alpha >= kAlphaVisibleThreshold;
}

@end

[aUIImage colorAtPixel:point] is a category-method that is attached.