iOS父控件alpha不影响子控件

今天看见一个需要，父控件的背景色需要设置alpha值，子控件不需要

• 首先想到的是这样处理，但这样父控的alpha值会影响到子控件

/* Create a new color object in CI's default RGB colorspace
   which is kCGColorSpaceSRGB or, if running on OSX before 10.10,
   kCGColorSpaceGenericRGB. */
+ (instancetype)colorWithRed:(CGFloat)r green:(CGFloat)g blue:(CGFloat)b alpha:(CGFloat)a;

• 查了下可以用这样处理

// Returns a color in the same color space as the receiver with the specified alpha component.
- (UIColor *)colorWithAlphaComponent:(CGFloat)alpha;

• 举个例子🌰:

 self.view.backgroundColor = [[UIColor redColor] colorWithAlphaComponent:0.3];