有個需求，視圖的右邊需要漸隱，如下圖：（這里只是隨便拿個界面做下測試）

Paste_Image.png

要求整個view漸漸alpha變透明，包括view上的子view，需要一起變透明。

拿起鍵盤就是干：

-(void)testAlpha{
    [self.view layoutIfNeeded];
    UIColor *color1 = [UIColor colorWithRed:(0)  green:(0)  blue:(0)   alpha:1.0];
    UIColor *color2 = [UIColor colorWithRed:(0)  green:(0)  blue:(0)  alpha:0.8];
    UIColor *color3 = [UIColor colorWithRed:(0)  green:(0)  blue:(0)  alpha:0.2];
    NSArray *colors = [NSArray arrayWithObjects:(id)color1.CGColor, color2.CGColor,color3.CGColor, nil];
    NSArray *locations = [NSArray arrayWithObjects:@(0.0), @(0.7),@(1.0), nil];
    CAGradientLayer *gradientLayer = [CAGradientLayer layer];
    gradientLayer.colors = colors;
    gradientLayer.locations = locations;
    gradientLayer.frame = _inputView.bounds;
    gradientLayer.startPoint = CGPointMake(0, 0);
    gradientLayer.endPoint   = CGPointMake(1, 0);
    _inputView.layer.mask = gradientLayer;
}

搞定！