Wrapping UIKit background tasks with ReactiveCocoa (http://sharplet.me/post/123363708110/wrapping-uikit-background-tasks-with)

UIApplication+SHReactiveBackgroundTask.h

/// An API for managing UIKit background tasks by composing signals.
@interface UIApplication (SHReactiveBackgroundTask)

/// Creates a signal that wraps an underlying signal in a background task.
/// Upon subscription, starts a background task, and then automatically ends
/// the background task when the underlying signal completes or errors.
/// If the background task expires, the subscription to the underlying signal
/// will automatically be disposed of.
///
/// @note If the call to `-beginBackgroundTaskWithExpirationHandler:` returns
/// `UIBackgroundTaskInvalid`, the returned signal will immediately send an error,
/// and `signalBlock` will never be invoked.
- (RACSignal *)sh_backgroundTaskWithSignal:(RACSignal *(^)(void))signalBlock;

@end

UIApplication+SHReactiveBackgroundTask.m

@implementation UIApplication (SHReactiveBackgroundTask)

- (RACSignal *)sh_backgroundTaskWithSignal:(RACSignal *(^)(void))signalBlock {
  return [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
    __block RACDisposable *taskDisposable;

    UIBackgroundTaskIdentifier taskIdentifier = [self beginBackgroundTaskWithExpirationHandler:^{
      [taskDisposable dispose];
    }];

    if (taskIdentifier == UIBackgroundTaskInvalid) {
      NSError *error = [NSError errorWithDomain:@"me.sharplet.ReactiveBackgroundTask" code:0 userInfo:@{
        NSLocalizedDescriptionKey: @"Running in the background is not possible."
      }];
      [subscriber sendError:error];
      return nil;
    }

    RACSignal *taskSignal = signalBlock();

    taskDisposable = [[taskSignal
      finally:^{
        [self endBackgroundTask:taskIdentifier];
      }]
      subscribe:subscriber];

    return taskDisposable;
  }];
}

@end