WatchKit return reply() inside a block in handleWatchKitExtensionRequest:

Question

I saw this SO post where apparently data was being fetched and returned to the Watch extension like so:

- (void)application:(UIApplication *)application handleWatchKitExtensionRequest:(NSDictionary *)userInfo reply:(void ( ^)( NSDictionary * ))reply
{
  if ( [[userInfo objectForKey:@"request"] isEqualToString:@"getData"] )
 {
  // get data
  // ...
  reply( data );
 }
}

But when I try to call 'reply()' inside a block after getting network data like so:

__block UIBackgroundTaskIdentifier watchKitHandler;

watchKitHandler = [[UIApplication sharedApplication] beginBackgroundTaskWithName:@"backgroundTask"
                                                               expirationHandler:^{
                                                                   watchKitHandler = UIBackgroundTaskInvalid;
                                                               }];   
- (void)application:(UIApplication *)application handleWatchKitExtensionRequest:(NSDictionary *)userInfo reply:(void ( ^)( NSDictionary * ))reply
{ 

NSMutableDictionary *response = [NSMutableDictionary dictionary];
[ClassObject getDataWithBlock:^(BOOL succeeded, NSError *error){
        
        if (succeeded)
        {
            [response setObject:@"update succeded" forKey:@"updateKey"];
            reply(response);
            
        }
        else
        {
            if (error)
            {
                [response setObject:[NSString stringWithFormat:@"update failed: %@", error.description] forKey:@"updateKey"]; 
                reply(response);
            }
            else
            {
                [response setObject:@"update failed with no error" forKey:@"updateKey"];
                reply(response);
            }
        }
    }];
}

dispatch_after(dispatch_time( DISPATCH_TIME_NOW, (int64_t)NSEC_PER_SEC * 180), dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    [[UIApplication sharedApplication] endBackgroundTask:watchKitHandler];
});

I get this error:

"The UIApplicationDelegate in the iPhone App never called reply() in -[UIApplicationDelegate application:handleWatchKitExtensionRequest:reply:]"

So I guess I have to call reply() immediately and the only way to send fresh network data after WatchKit wakes up the parent app is to use MMWormhole?

John · Accepted Answer · 2015-05-11T19:11:08.283

To make sure that your asynchronous data fetch does not return immediately (without calling reply), you may try the following:

- (void)application:(UIApplication *)application handleWatchKitExtensionRequest:(NSDictionary *)userInfo reply:(void ( ^)( NSDictionary * ))reply
{ 
    __block UIBackgroundTaskIdentifier watchKitHandler;

    watchKitHandler = [[UIApplication sharedApplication] beginBackgroundTaskWithName:@"backgroundTask"
                                                               expirationHandler:^{
                                                                   watchKitHandler = UIBackgroundTaskInvalid;
                                                               }];  

   NSMutableDictionary *response = [NSMutableDictionary dictionary];

   dispatch_semaphore_t sema = dispatch_semaphore_create(0);

   [ClassObject getDataWithBlock:^(BOOL succeeded, NSError *error){

        if (succeeded)
        {
            [response setObject:@"update succeded" forKey:@"updateKey"];
            reply(response);

        }
        else
        {
            if (error)
            {
                [response setObject:[NSString stringWithFormat:@"update failed: %@", error.description] forKey:@"updateKey"]; 

                dispatch_semaphore_signal(sema);

                reply(response);
            }
            else
            {
                [response setObject:@"update failed with no error" forKey:@"updateKey"];

                dispatch_semaphore_signal(sema);

                reply(response);
            }
        }
    }];

    dispatch_semaphore_wait(sema, DISPATCH_TIME_FOREVER);

    dispatch_after(dispatch_time( DISPATCH_TIME_NOW, (int64_t)NSEC_PER_SEC * 1), dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    [[UIApplication sharedApplication] endBackgroundTask:watchKitHandler];
  });
}

I already was wrapping it in a background task. I should have made this clear and have updated my question. I even tried changing the time to 180 seconds but it still returns immediately with the error. Do you run a block in 'get data' in your example? — Michael Leveton, May 09 '15 at 17:14
Hello, I have changed my answer accordingly. In this way, one second is enough since the program waits at `dispatch_semaphore_wait(sema, DISPATCH_TIME_FOREVER);` until `dispatch_semaphore_signal(sema);` is executed. Does it work? — John, May 09 '15 at 20:27
it's not working for me. I did the same. Just doesn't work for me :( — Min Soe, May 26 '15 at 15:49

rmp · Answer 2 · 2015-05-26T19:29:05.587

I think you got your code mixed up. You need to move the beginBackgroundTaskWithName to be inside your handleWatchKitExtensionRequest Make it the first thing you do, then call your function.

Simplified example:

-(void)application:(UIApplication *)application handleWatchKitExtensionRequest:(NSDictionary *)userInfo reply:(void (^)(NSDictionary *replyInfo))reply{


    UIApplication *app = [UIApplication sharedApplication];

    UIBackgroundTaskIdentifier bgTask __block = [app beginBackgroundTaskWithName:@"watchAppRequest" expirationHandler:^{

        NSLog(@"Background handler called. Background tasks expirationHandler called.");
        [[UIApplication sharedApplication] endBackgroundTask:bgTask];
        bgTask = UIBackgroundTaskInvalid;

    }];

    //do your background task(s) here
    if([requestString isEqualToString:@“myRequest"]){

            //send reply back to watch
            reply();
    }

    //end background task
    [app endBackgroundTask:bgTask];
    bgTask=UIBackgroundTaskInvalid;

}

score 0 · Answer 3 · answered May 26 '15 at 16:56

Always refer to official documentation. Official Documentation

The following code works for me.

__block UIBackgroundTaskIdentifier bgTask = [application beginBackgroundTaskWithName:@"MyTask" expirationHandler:^{
                // Clean up any unfinished task business by marking where you
                // stopped or ending the task outright.
                [application endBackgroundTask:bgTask];
                bgTask = UIBackgroundTaskInvalid;
        }];

// Start the long-running task and return immediately.
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

// Do the work associated with the task, preferably in chunks.

    [ClassObject getDataWithBlock:^(BOOL succeeded, NSError *error){

        if (succeeded)
        {
            [response setObject:@"update succeded" forKey:@"updateKey"];
            reply(response);

        }
        else
        {
            if (error)
            {
                [response setObject:[NSString stringWithFormat:@"update failed: %@", error.description] forKey:@"updateKey"]; 

                reply(response);
            }
            else
            {
                [response setObject:@"update failed with no error" forKey:@"updateKey"];

                reply(response);
            }
        }
    }];
    [application endBackgroundTask:bgTask];
    bgTask = UIBackgroundTaskInvalid;
});

WatchKit return reply() inside a block in handleWatchKitExtensionRequest:

3 Answers3

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