iPhone -ошибка с отправкой изображений и текста по bluetooth

У меня проблема с фреймворком GameKit. В моем приложении я хочу отправить текст или изображение. Теперь, когда я отправляю изображение из UIImagePicker, оно работает хорошо. Когда я отправляю текст, он не показывает тот же UIAlertViewдля изображений без изображения. Вот.h:

    #import <UIKit/UIKit.h>
#import <GameKit/GameKit.h>

@interface ViewController : UIViewController <GKPeerPickerControllerDelegate, GKSessionDelegate, UIActionSheetDelegate, UINavigationControllerDelegate, UIImagePickerControllerDelegate> {
    GKSession *currentSession;
    IBOutlet UITextField *txtMessage;
    IBOutlet UIButton *connect;
    IBOutlet UIButton *disconnect;
    GKPeerPickerController *picker;
    UIImagePickerController *imgPicker;
    BOOL isText;
    UIImage *_image;
}
@property (nonatomic, retain) GKSession *currentSession;
@property (nonatomic, retain) UITextField *txtMessage;
@property (nonatomic, retain) UIButton *connect;
@property (nonatomic, retain) UIButton *disconnect;
-(IBAction) btnSend:(id) sender;
-(IBAction) btnConnect:(id) sender;
-(IBAction) btnDisconnect:(id) sender;
-(IBAction)chooseImageData:(id)sender;
@end

И.m:

#import "ViewController.h"
#import <GameKit/GameKit.h>

@implementation ViewController

@synthesize currentSession;
@synthesize txtMessage;
@synthesize connect;
@synthesize disconnect;

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Release any cached data, images, etc that aren't in use.
}

#pragma mark - View lifecycle

- (void)viewDidLoad {
    [connect setHidden:NO];
    [disconnect setHidden:YES];
    [super viewDidLoad];
}

- (void)peerPickerController:(GKPeerPickerController *)picker
              didConnectPeer:(NSString *)peerID
                   toSession:(GKSession *) session {
    self.currentSession = session;
    session.delegate = self;
    [session setDataReceiveHandler:self withContext:nil];
    picker.delegate = nil;
    [picker dismiss];
}

-(IBAction) btnConnect:(id) sender {
    picker = [[GKPeerPickerController alloc] init];
    picker.delegate = self;
    picker.connectionTypesMask = GKPeerPickerConnectionTypeNearby;
    [connect setHidden:YES];
    [disconnect setHidden:NO];
    [picker show];
}

- (void)peerPickerControllerDidCancel:(GKPeerPickerController *)picker
{
    picker.delegate = nil;
    [connect setHidden:NO];
    [disconnect setHidden:YES];
}   

-(IBAction) btnDisconnect:(id) sender {
    [self.currentSession disconnectFromAllPeers];
    currentSession = nil;
    [connect setHidden:NO];
    [disconnect setHidden:YES];
}

- (void)session:(GKSession *)session
           peer:(NSString *)peerID
 didChangeState:(GKPeerConnectionState)state {
    switch (state)
    {
        case GKPeerStateConnected:
            NSLog(@"connected");
            break;
        case GKPeerStateDisconnected:
            NSLog(@"disconnected");
            currentSession = nil;
            [connect setHidden:NO];
            [disconnect setHidden:YES];
            break;
    }
}

- (void) mySendDataToPeers:(NSData *) data
{
    if (currentSession)
        [self.currentSession sendDataToAllPeers:data
                                   withDataMode:GKSendDataReliable
                                          error:nil];
}
- (void) mySendImageToPeers:(NSData *) data
{
    if (currentSession)
        [self.currentSession sendDataToAllPeers:data
                                   withDataMode:GKSendDataReliable
                                          error:nil];
}

-(IBAction) btnSend:(id) sender
{
    //---convert an NSString object to NSData---
    NSData* data;
    NSString *str = [NSString stringWithString:txtMessage.text];
    data = [str dataUsingEncoding: NSASCIIStringEncoding];
    [self mySendDataToPeers:data];
}

- (void) receiveData:(NSData *)data
            fromPeer:(NSString *)peer
           inSession:(GKSession *)session
             context:(void *)context {
    //---convert the NSData to NSString---

    if (isText) {
        isText = YES;
    NSString* str;
    str = [[NSString alloc] initWithData:data encoding:NSASCIIStringEncoding];
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Messaggio"
                                                    message:str
                                                   delegate:self
                                          cancelButtonTitle:@"OK"
                                          otherButtonTitles:nil];
    [alert show];
    }
    else
    {
        UIImage *tempSentImg = [UIImage imageWithData:data];
        _image = tempSentImg;
        UIAlertView* alert = [[UIAlertView alloc] initWithTitle:@"Immagine"
                                                        message:@"\n\n\n\n\n"
                                                       delegate:self
                                              cancelButtonTitle:@"OK"
                                              otherButtonTitles:nil];
        UIImageView *imageView = [[UIImageView alloc] initWithImage:_image];
        CGFloat imageHeight = 100;
        CGFloat imageWidth = imageHeight * _image.size.width / _image.size.height;
        imageView.frame = CGRectMake(floor((284 - imageWidth)/2), 47, imageWidth, imageHeight);
        [alert addSubview:imageView];
        [alert show];
        return;
    }

}

-(IBAction)chooseImageData:(id)sender {
    [self performSelector: @selector(dialogOtherAction)];
}

- (void)dialogOtherAction {
    UIActionSheet *actionSheet = [[UIActionSheet alloc] initWithTitle:nil
                                                             delegate:self 
                                                    cancelButtonTitle:NSLocalizedString(@"Annulla", @"")
                                               destructiveButtonTitle:nil
                                                    otherButtonTitles:NSLocalizedString(@"Scegli dalla libreria", @""),
                                  NSLocalizedString(@"Scatta una foto", @""),nil];
    actionSheet.actionSheetStyle = UIActionSheetStyleBlackTranslucent;
    [actionSheet showInView:self.view];
}

- (void)actionSheet:(UIActionSheet *)actionSheet clickedButtonAtIndex:(NSInteger)buttonIndex
{
    if (buttonIndex == 0)
    {
        imgPicker = [[UIImagePickerController alloc] init];
        imgPicker.sourceType =  UIImagePickerControllerSourceTypePhotoLibrary;
        imgPicker.allowsEditing = NO;
        imgPicker.delegate = self;

        [self presentModalViewController:imgPicker animated:YES];   
     }
    else if (buttonIndex == 1)
    {
        imgPicker = [[UIImagePickerController alloc] init];
        imgPicker.sourceType = UIImagePickerControllerSourceTypeCamera;
        imgPicker.delegate = self;
        imgPicker.allowsEditing = NO;
        [self presentModalViewController:imgPicker animated:YES];
    }
}

-(void)actionSheet:(UIActionSheet *)actionSheet didDismissWithButtonIndex:(NSInteger)buttonIndex {
    [actionSheet dismissWithClickedButtonIndex:0 animated:YES];
}

- (void)imagePickerController:(UIImagePickerController *)imgPicker didFinishPickingMediaWithInfo:(NSDictionary *)info
{
   [self dismissModalViewControllerAnimated:YES];    

    UIImage *image = [info objectForKey:@"UIImagePickerControllerOriginalImage"];
    [self performSelector: @selector(btnImageSend:) withObject: image afterDelay: 1.0];
}
-(IBAction) btnImageSend:(UIImage *)image
{
    //---convert an NSString object to NSData---
    NSData* data;
    data = UIImagePNGRepresentation(image);
    [self mySendImageToPeers:data];
}


- (void)viewDidUnload
{
    [super viewDidUnload];
    // Release any retained subviews of the main view.
    // e.g. self.myOutlet = nil;
}

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
}

- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];
}

- (void)viewWillDisappear:(BOOL)animated
{
    [super viewWillDisappear:animated];
}

- (void)viewDidDisappear:(BOOL)animated
{
    [super viewDidDisappear:animated];
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    // Return YES for supported orientations
    return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
}

@end