How to make a UIView have an effect of transparent gradient?

问题

I want to make a UIView have an effect of transparent gradient from the middle to the left and right. Like in this example:

enter image description here

The word 籍 has the desired effect. This view is achieved by the class MarqueeLabel. I examined the source code, it is likely implemented by class CALayer.

回答1:

You can use CAGradientLayer as following.

gradientLayer = [CAGradientLayer layer];
gradientLayer.frame = baseView.bounds;
gradientLayer.startPoint = CGPointMake(0.5,0.0);
gradientLayer.endPoint = CGPointMake(0.5,1.0);
gradientLayer.locations = @[@(0.0), @(0.2), @(1.0)];
gradientLayer.colors = @[(id)[UIColor colorWithWhite:1.0 alpha:0.9].CGColor,
                         (id)[UIColor colorWithWhite:1.0 alpha:0.3].CGColor,
                         (id)[UIColor colorWithWhite:1.0 alpha:0.0].CGColor];
[baseView.layer addSublayer:gradientLayer];

CAGradientLayer supports several properties to make natural gradient, such as setting gradient direction by startPoint and endPoint, changing color curve by locations and colors.

You also make a transparent effect by using alpha channel of color.

回答2:

Screenshot

Swift code

let mask = CAGradientLayer()
mask.startPoint = CGPointMake(0.0, 0.5)
mask.endPoint = CGPointMake(1.0, 0.5)
let whiteColor = UIColor.whiteColor()
mask.colors = [whiteColor.colorWithAlphaComponent(0.0).CGColor,whiteColor.colorWithAlphaComponent(1.0),whiteColor.colorWithAlphaComponent(1.0).CGColor]
mask.locations = [NSNumber(double: 0.0),NSNumber(double: 0.2),NSNumber(double: 1.0)]
mask.frame = label.bounds
label.layer.mask = mask

回答3:

In Swift 4: for top to bottom transparent gradient.

let gradient = CAGradientLayer()
gradient.startPoint = CGPoint(x: 0.5, y: 0.0)
gradient.endPoint = CGPoint(x: 0.5, y: 0.6)
let whiteColor = UIColor.white
gradient.colors = [whiteColor.withAlphaComponent(0.0).cgColor, whiteColor.withAlphaComponent(1.0).cgColor, whiteColor.withAlphaComponent(1.0).cgColor]
gradient.locations = [NSNumber(value: 0.0),NSNumber(value: 0.2),NSNumber(value: 1.0)]
gradient.frame = gradientView.bounds
gradientView.layer.mask = gradient

回答4:

Swift 3:

let mask = CAGradientLayer()
mask.startPoint = CGPoint(x: 0, y: 0.5)
mask.endPoint = CGPoint(x:1.0, y:0.5)
let whiteColor = UIColor.white
mask.colors = [whiteColor.withAlphaComponent(0.0).cgColor,whiteColor.withAlphaComponent(1.0),whiteColor.withAlphaComponent(1.0).cgColor]
mask.locations = [NSNumber(value: 0.0),NSNumber(value: 0.2),NSNumber(value: 1.0)]
mask.frame = view.bounds
view.layer.mask = mask

回答5:

Use clear color instead of set the alpha value.

let gradientLayer = CAGradientLayer()
gradientLayer.startPoint = CGPoint(x: 0, y: 0.5)
gradientLayer.endPoint = CGPoint(x: 1, y: 0.5)
gradientLayer.colors = [UIColor.clear.cgColor, UIColor.white.cgColor, UIColor.white.cgColor]
gradientLayer.locations = [0, 0.2, 1]
gradientLayer.frame = gradientView.bounds
gradientView.layer.mask = gradientLayer

来源：https://stackoverflow.com/questions/36490270/how-to-make-a-uiview-have-an-effect-of-transparent-gradient

标签

ios

swift

uiview

gradient