How to make selected area of a superview transparent - ios

Question

Is there any way we can make only the selected area of a superview transparent? I have a UIView with black (alpha 0.5) background color. I am putting some hollow circles on the UIView and want the underneath UIView to be transparent so that I could see through it. Any idea
- (id)initWithFrame:(CGRect)iFrame andHollowFrames:(NSArray *)iHollowFrames withRadius:(NSNumber *)iRadius {
if ((self = [super initWithFrame:iFrame]) != nil) {
self.hollowFrames = [[NSSet setWithArray:iHollowFrames] allObjects];
self.hollowCircleRadius = iRadius;
[self addShadowView];
}
return self;
}
- (void)addShadowView {
UIBezierPath *path = [UIBezierPath bezierPathWithRoundedRect:CGRectMake(0, 0, self.bounds.size.width, self.bounds.size.height) cornerRadius:0];
for (NSValue *point in self.hollowFrames) {
UIBezierPath *circlePath = [UIBezierPath bezierPathWithRoundedRect:CGRectMake(point.CGPointValue.x - self.hollowCircleRadius.floatValue, point.CGPointValue.y - self.hollowCircleRadius.floatValue, 2.0 * self.hollowCircleRadius.floatValue, 2.0 * self.hollowCircleRadius.floatValue) cornerRadius:self.hollowCircleRadius.floatValue];
[path appendPath:circlePath];
}
[path setUsesEvenOddFillRule:YES];
CAShapeLayer *fillLayer = [CAShapeLayer layer];
fillLayer.path = path.CGPath;
fillLayer.fillRule = kCAFillRuleEvenOdd;
fillLayer.fillColor = [UIColor blackColor].CGColor;
fillLayer.opacity = 0.5;
[self.layer addSublayer:fillLayer];
}

Answer 1

Here is a UIView subclass solution. In order for this to work you must leave the superviews backgroundColor property as nil witch is the default value. If this UIView-subclass is in the storyboard then make sure you set the background color to "Clear color" in the attributes inspector.
- (void)drawRect:(CGRect)rect
{
CGContextRef ctx = UIGraphicsGetCurrentContext();
UIColor *blackBackgroundColor = [UIColor colorWithRed:0 green:0 blue:0 alpha:0.5];
CGContextSetFillColorWithColor(ctx, blackBackgroundColor.CGColor);
CGContextFillRect(ctx, rect);
CGRect transparentPart = CGRectMake(10, 10, 120, 80);
CGContextClearRect(ctx, transparentPart);
}