使用iOS中的CTCallCenter检测呼叫状态

Question

以下代码可以正常工作以在iPhone 4s（运行iOS 5.1.1）中获取应用程序中的呼叫状态，但不能在iPhone 5s（运行iOS 7.1.2）中运行。可以帮助任何人吗？

在MyViewController.h中

@property (nonatomic, strong) CTCallCenter* callCenter;

在MyViewController.m

中

- (void)viewDidLoad
{
    [self registerForCalls];
}

- (void) registerForCalls {

    self.callCenter = [[CTCallCenter alloc] init];

    [callCenter setCallEventHandler: ^(CTCall* call) {
        if (call.callState == CTCallStateDisconnected)
        {
            NSLog(@"Call has been disconnected");
        }
        else if (call.callState == CTCallStateConnected)
        {
            NSLog(@"Call has just been connected");
        }
        else if (call.callState == CTCallStateIncoming)
        {
            NSLog(@"Call is incoming");
        }
        else if (call.callState == CTCallStateDialing)
        {
            NSLog(@"Call is Dialing");
        }
        else
        {
            NSLog(@"None of the conditions");
        }
    }];
}