Multipeer Connectivity Slowing View Creation

Question

I have an app that uses Multipeer Connectivity and, when one device sends data to the others in the group, all the others are supposed to get a notification on their screen that data is sent to them and they then have the option whether or not to accept it. The problem that I am running into time and time again, no matter what I do, is that the notification view takes at least five seconds to show up, and most times longer (I even made my own quick and crude substitute for a UIAlertView -as shown commented out- in case the UIAlertView was the problem, which didn't solve anything). I have the notification code running inside the session:didReceiveData:fromPeer method of this API. And my NSLog's above and below the UIAlertView and my crude replacement both show in quick succession, it just takes forever for the view to show up. Any ideas? Here is my code:

-(void)session:(MCSession *)session didReceiveData:(NSData *)data fromPeer:(MCPeerID *)peerID{
    NSLog(@"DATA RECEIVED: %lu bytes!", (unsigned long)data.length);
    dataReceived = data;
    receivedDataDict = [[NSMutableDictionary alloc] init];
    NSLog(@"Initializing ReceivedDataDict");
    receivedDataDict = [NSKeyedUnarchiver unarchiveObjectWithData:dataReceived];
    NSLog(@"ReceivedDataDict is Unarchived");

    UIAlertView *alert = [[UIAlertView alloc]initWithTitle: @"Hey!"
                                               message: [[NSString alloc] initWithFormat:@"%@ is trying to send you data! Do you accept?", [peerID displayName]]
                                              delegate: self
                                     cancelButtonTitle:@"Nuh Uh!!"
                                     otherButtonTitles:@"Ok, I guess.",nil];
    [alert show];

//    [self.view addSubview:greyOut];
//    
//    CGRect headsUpViewRect = CGRectMake(236, 400, 300, 200);
//    headsUpView = [[UIView alloc] initWithFrame:headsUpViewRect];
//    headsUpView.backgroundColor = [UIColor whiteColor];
//    headsUpView.layer.cornerRadius = 10;
//    
//    CGRect headsUpTitleLblRect = CGRectMake(20, 20, 260, 30);
//    UILabel *headsUpTitleLbl = [[UILabel alloc] initWithFrame:headsUpTitleLblRect];
//    headsUpTitleLbl.text = [[NSString alloc] initWithFormat:@"%@ is trying to send you matches!", [peerID displayName]];
//    headsUpTitleLbl.font = [UIFont systemFontOfSize:15];
//    headsUpTitleLbl.textAlignment = NSTextAlignmentCenter;
//    [headsUpView addSubview:headsUpTitleLbl];
//    
//    CGRect headsUpSubTitleLblRect = CGRectMake(50, 60, 200, 30);
//    UILabel *headsUpSubTitleLbl = [[UILabel alloc] initWithFrame:headsUpSubTitleLblRect];
//    headsUpSubTitleLbl.text = @"Do you accept their gift?";
//    headsUpSubTitleLbl.font = [UIFont systemFontOfSize:10];
//    headsUpSubTitleLbl.textAlignment = NSTextAlignmentCenter;
//    [headsUpView addSubview:headsUpSubTitleLbl];
//    
//    CGRect confirmBtnRect = CGRectMake(200, 120, 80, 50);
//    UIButton *confirmBtn = [UIButton buttonWithType:UIButtonTypeSystem];
//    [confirmBtn addTarget:self action:@selector(headsUpViewClickedButtonAtIndex1) forControlEvents:UIControlEventTouchUpInside];
//    confirmBtn.frame = confirmBtnRect;
//    [confirmBtn setTitle:@"Of Course!" forState:UIControlStateNormal];
//    confirmBtn.backgroundColor = [UIColor colorWithWhite:0.8 alpha:1.0];
//    [headsUpView addSubview:confirmBtn];
//    confirmBtn.layer.cornerRadius = 5;
//    
//    CGRect cancelBtnRect = CGRectMake(20, 120, 80, 50);
//    UIButton *cancelBtn = [UIButton buttonWithType:UIButtonTypeSystem];
//    [cancelBtn addTarget:self action:@selector(cancelHeadsUpView) forControlEvents:UIControlEventTouchUpInside];
//    cancelBtn.frame = cancelBtnRect;
//    [cancelBtn setTitle:@"Nuh Uh!!" forState:UIControlStateNormal];
//    cancelBtn.backgroundColor = [UIColor colorWithWhite:0.8 alpha:1.0];
//    [headsUpView addSubview:cancelBtn];
//    cancelBtn.layer.cornerRadius = 5;
//    
//    headsUpView.transform = CGAffineTransformMakeScale(0.01, 0.01);
//    [self.view addSubview:headsUpView];
//    [UIView animateWithDuration:0.3 delay:0 options:UIViewAnimationOptionCurveEaseOut
//                     animations:^{
//                         headsUpView.transform = CGAffineTransformIdentity;
//                     }
//                     completion:^(BOOL finished){
//                     }];

    NSLog(@"Should Show Alert");
}

The NSLog(@"Should Show Alert") appears in my console window LONG before the view actually appears for either coding approach. The data transfer works as it should and all devices get the data they are supposed to get, but I want to know why it takes so long for such a small user interface thing to load.

Answer 1

Turns out my user interface code was not being called as part of the main thread, so my solution turned out to be looking like this:

dispatch_async(dispatch_get_main_queue(), ^(void) {
     UIAlertView *alert = …
});

Shout out to the guys over at the Apple Developer Forum for helping me out

Answer 2

I had a few UI changes to display so just changed it to this based on teamDriven's and Marco's comments. I was struggling trying to understand what was blocking the main thread, and never thought to think that I wasn't on the main thread to begin with

// received data from remote peer
- (void)session:(MCSession *)session
 didReceiveData:(NSData *)data
       fromPeer:(MCPeerID *)peerID
{
    NSLog(@"session:didReceiveData:fromPeer");

    // didReceiveData is on background thread, and we have UI activity that we want on main thread
    dispatch_async(dispatch_get_main_queue(), ^(void) {
        [self processReceivedData:data fromPeer:peerID];
    });
}


// process received data
- (void)processReceivedData:(NSData *)data fromPeer:(MCPeerID *)peerID
{
     // UI stuff
}

Answer 3

I don't use ARC. I found it necessary to place the session's release in a queue to avoid a delay:

 -(void)dealloc{
     if(theSession)
         dispatch_async(dispatch_get_main_queue(), ^{
            [theSession release];
          });
      //   more dealloc
  }