在reactivecocoa4中观察开关和触发Action似乎如下所示。但在reactivecocoa5中无法弄清楚。mediaTypeSwich.rac_signalForControlEvents(.ValueChanged).flattenMap{(sender:AnyObject!)->RACStream!inletsegment=senderasUISegmentedControlswitchsegment.selectedSegmentIndex{case0:returnself.photoSignal()default:returnself.videoSignal()}}