How to mask a UILabel in iOS - Objective-C

I want to sub-class a UIView and place four UILabels over top开发者_高级运维 one another ; top label will be the MASK, 2nd label will be a normal label with text, the 3rd label is a label with solid background with no text. the bottom label will the same as the top 2nd label with a different color font. when i sent the width of the third label it will cover up the bottom label showing a partial view of the text. I want to have the 2nd text be one color while the uncoverd bottom label display another color font.

Is this possibe? If someone can explain how to mask in objective-C that will help too.

I trying to build a UIView that acts like a progress bar, as the bar fill to 60%, I want to top text to show in white font color, when the bottom text shows in a different color.

You could do it with two UILabels, one on the bottom, and one embedded in another view on top.

UILabel *bottomLabel = ...;
[self.view addSubview:bottomLabel];

UIView *topContainer = [[UIView alloc] initWithFrame:bottomLabel.frame];
topContainer.clipsToBounds = YES;
topContainer.opaque = NO;
topContainer.backgroundColor = [UIColor clearColor];

UILabel *topLabel = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, bottomLabel.frame.size.width, bottomLabel.frame.size.height)];
topLabel.text = bottomLabel.text;
topLabel.opaque = NO;
topLabel.backgroundColor = [UIColor clearColor];

[topContainer addSubview:topLabel];
[self.view addSubview:topContainer];

Then, when you want to change the progress, you'd set the width of topContainer. This should clip topLabel.

Rather than using four UILabels, why not subclass UILabel and draw it yourself in the drawRect: method? It would look something like:

- (void)drawRect:(CGRect)rect {
    CGContextRef context = UIGraphicsGetCurrentContext();

    // Set the mask
    CGContextClipToMask(context, self.bounds, /* mask image */);

    // Draw the text in a different font
    [self.text drawInRect:rect withFont:/* alternate font */];

    // Draw a solid background
    CGContextSetRGBFillColor(context, ...);
    CGContextFillRect(context, rect);

    // Draw the text normally
    [super drawRect:rect];
}

You could make the masking image and the alternate font properties of your subclass, for convenience.