title: VoIP Push not work for an iOS SDK Demo
body: <p>I'm developing an iOS SDK with VoIP PushKit. And here is the code in SDK when receive a push notification</p>
  
  <pre><code>- (void)onReceiveMessagecontent:(NSString *)content{    
      if (content &amp;&amp; ![content isEqualToString:@""]) {
          if ([[WalkieTalkie sharedWT].delegate respondsToSelector:@selector(onPushMessage:)]) {
              [[WalkieTalkie sharedWT].delegate onPushMessage:content];
          }
      }
  }
  </code></pre>
  
  <p>Here is the code in SDK Demo MainViewController.m where delegate will be called :</p>
  
  <pre><code>- (void)onPushMessage:(NSString *)messageContent{
      NSString *content = [NSString stringWithFormat:@"on recive push message: %@", messageContent];
  
      if ([[UIApplication sharedApplication] applicationState] == UIApplicationStateActive) {
          UIAlertController *alert = [UIAlertController alertControllerWithTitle:@"收到推送" message:content preferredStyle:UIAlertControllerStyleAlert];
          UIAlertAction *cancelButton = [UIAlertAction actionWithTitle:@"取消" style:UIAlertActionStyleCancel handler:nil];
          [alert addAction:cancelButton];
          [self presentViewController:alert animated:YES completion:nil];
      } else{
          dispatch_async(dispatch_get_main_queue(), ^{
              UILocalNotification *notification = [[UILocalNotification alloc] init];
              notification.fireDate = [NSDate dateWithTimeIntervalSinceNow:5];
              notification.alertBody = content;
              notification.timeZone = [NSTimeZone defaultTimeZone];
              notification.soundName = UILocalNotificationDefaultSoundName;
              notification.applicationIconBadgeNumber = 1;
  
              [[UIApplication sharedApplication] scheduleLocalNotification:notification];
          });
      }
  }
  </code></pre>
  
  <p>When app is active the UIAlertController works well, but when I kill the app makes it in background mode the UILocalNotification never fire. However I can see some device log from Xcode that prove the remote notification had already been called and run the line of code :<code>[[WalkieTalkie sharedWT].delegate onPushMessage:content];</code> in SDK. But the demo app just show nothing, none reaction. Did I put the delegate codes in a wrong place? Or just the SDK is active and app is still in background? I have no idea, please give me some advice, thanks a lot!</p>