如何使UIView具有透明漸變效果？

Question

我想做一個UIView有一個從中間到左側和右側透明漸變的效果。像在本例中：

字籍具有期望的效果。該視圖由類MarqueeLabel實現。我檢查了源代碼，它很可能由類CALayer實施。

Answer 1

您可以使用CAGradientLayer如下。

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支持幾種屬性，使自然梯度，例如通過startPoint和endPoint設置梯度方向，通過locations和colors變色曲線。

您還可以通過使用alpha通道的顏色來製作透明效果。

Answer 2

截圖

SWIFT代碼

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 

Answer 3

夫特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