解决方法
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In iOS 8 and later,voice-over-IP (VoIP) apps register for UIRemoteNotificationTypeVoIP push notifications instead of using this method. Using push notifications eliminates the need for a timeout handler to check in with the VoIP service. Instead,when a calls arrives for the user,the VoIP service sends a VoIP push notification to the user’s device. Upon receiving this notification,the device launches or wakes the app as needed so that it can handle the incoming call.