iOS UIButton with transparent title on white background - ios

Question

I have a custom UIButton with transparent background and white title.
I'm looking for a simple solution to invert it on highlight (white background and transparent title) as it is achieved on system UISegmentedControl.
Is there simpler solution than inverting alpha on snapshot used as a CALayer mask?
If not, could you tell how can I invert CALayer alpha?

Answer 1

You can draw the text on a CGContext using Destination Out as blend mode.
This code seems to work:
- (void)viewDidLoad
{
[super viewDidLoad];
self.view.backgroundColor = [UIColor greenColor];
UIFont* font = [UIFont fontWithName:#"Helvetica-Bold" size:18];
NSString* buttonText = #"BUTTON";
CGSize buttonSize = CGSizeMake(200, 50);
NSDictionary* textAttributes = #{NSFontAttributeName:font};
CGSize textSize = [buttonText sizeWithAttributes:textAttributes];
UIGraphicsBeginImageContextWithOptions(buttonSize, NO, [[UIScreen mainScreen] scale]);
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGContextSetFillColorWithColor(ctx, [UIColor redColor].CGColor);
UIBezierPath *path = [UIBezierPath bezierPathWithRect:CGRectMake(0, 0, buttonSize.width, buttonSize.height)];
CGContextAddPath(ctx, path.CGPath);
CGContextFillPath(ctx);
CGContextSetBlendMode(ctx, kCGBlendModeDestinationOut);
CGPoint center = CGPointMake(buttonSize.width/2-textSize.width/2, buttonSize.height/2-textSize.height/2);
[#"BUTTON" drawAtPoint:center withAttributes:textAttributes];
UIImage* viewImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
UIImageView* imgView = [[UIImageView alloc] initWithImage:viewImage];
[self.view addSubview:imgView];
}
By the way, if you want to set the UIImage in a UIButton instead of just adding it to a view:
UIButton* boton = [[UIButton alloc] initWithFrame:CGRectMake(50, 50, viewImage.size.width, viewImage.size.height)];
[boton setBackgroundColor:[UIColor clearColor]];
[boton setTitleColor:[UIColor redColor] forState:UIControlStateNormal];
boton.titleLabel.font = font;
[boton setTitle:buttonText forState:UIControlStateNormal];
[boton setImage:viewImage forState:UIControlStateHighlighted];
[self.view addSubview:boton];

Answer 2

You could set
-(void)viewDidload: {
[yourButton setTitleColor:(UIColor *)color
forState:UIControlStateHighlighted];
[yourButton addTarget:self
action:#selector(changeButtonBackGroundColor:)
forControlEvents:UIControlEventTouchDown];
}
-(void)changeButtonBackGroundColor:(UIButton *)button {
[button setBackgroundColor:[UIColor yourColor]];
}
remember to change it back with events: UIControlEventTouchUpInside and UIControlEventTouchOutSide :)