在ITSwitch.m中
@property (readonly,strong) CALayer *rootLayer;
所以在快速写道：
var rootLayer:CALayer?
Use of module 'CALayer' as a type
在ITSwitch.m中
@property (readonly,strong) CALayer *rootLayer;
所以在快速写道：
var rootLayer:CALayer?
Use of module 'CALayer' as a type
