Display UIView with a UILabel text mask

问题:

I'm trying to add a UIView to a UILabel, so that the text is the view's mask, enabling me to do things like animated text backgrounds (much like the slide to unlock label on the lockscreen).

The way I was planning on doing it was using the mask property on the view's layer to mask it to the shape of the text. However, I cannot find a way to get the UILabel's text shape as a CALayer.

Is this even possible? I can only find solutions that override the -(void)drawRect: method in the UILabel, but this wouldn't give me much flexibility.

回答1:

UIView added the maskView property in iOS 8.0. Now, just create a UILabel to use as a mask for a UIView:

Objective-C:

UILabel* label = [[UILabel alloc] initWithFrame:self.view.frame];
label.text = @"Label Text";
label.font = [UIFont systemFontOfSize:70];
label.textAlignment = NSTextAlignmentCenter;
label.textColor = [UIColor whiteColor];

UIView* overlayView = [[UIView alloc] initWithFrame:self.view.frame];
overlayView.backgroundColor = [UIColor blueColor];
overlayView.maskView = label;
[self.view addSubview:overlayView];

Swift 2:

let label = UILabel.init(frame: view.frame)
label.text = "Label Text"
label.font = UIFont.systemFontOfSize(70)
label.textAlignment = .Center
label.textColor = UIColor.whiteColor()

let overlayView = UIView.init(frame: view.frame)
overlayView.backgroundColor = UIColor.blueColor()
overlayView.maskView = label

view.addSubview(overlayView)

This creates a crisp UILabel with UIColor.blueColor() color taken from overlayView.

回答2:

mopsled's solution is more flexible if you building for iOS 8+. However, if you're looking for a pre-iOS 8 answer, here it is.

---

Thanks to Linuxios for pointing me to this question. The key is to use CATextLayer instead of UILabel.

Objective-C:

CGRect textRect = {0, 100, self.view.frame.size.width, 100}; // rect to display the view in

CATextLayer* textMask = [CATextLayer layer];
textMask.contentsScale = [UIScreen mainScreen].scale; // sets the layer's scale to the main screen scale
textMask.frame = (CGRect){CGPointZero, textRect.size};
textMask.foregroundColor = [UIColor whiteColor].CGColor; // an opaque color so that the mask covers the text
textMask.string = @"Text Mask"; // your text here
textMask.font = (__bridge CFTypeRef _Nullable)([UIFont systemFontOfSize:30]); // your font here
textMask.alignmentMode = kCAAlignmentCenter; // centered text

UIView* view = [[UIView alloc] initWithFrame:textRect];
view.backgroundColor = [UIColor blueColor];
view.layer.mask = textMask; // mask the view to the textMask
[self.view addSubview:view];

Swift:

let textRect = CGRect(x: 0, y: 100, width: view.frame.size.width, height: 100) // rect to display the view in

let textMask = CATextLayer()
textMask.contentsScale = UIScreen.mainScreen().scale // sets the layer's scale to the main screen scale
textMask.frame = CGRect(origin: CGPointZero, size: textRect.size)
textMask.foregroundColor = UIColor.whiteColor().CGColor // an opaque color so that the mask covers the text
textMask.string = "Text Mask" // your text here
textMask.font = UIFont.systemFontOfSize(30) // your font here
textMask.alignmentMode = kCAAlignmentCenter // centered text

let bgView = UIView(frame: textRect)
bgView.backgroundColor = UIColor.blueColor()
bgView.layer.mask = textMask // mask the view to the textMask
view.addSubview(bgView)

回答3:

I create the custom maskLabel.

Check the answer https://stackoverflow.com/a/47105664/7371852

This is the result.