Just yesterday used a singleton in Objective-C due to a webservice that worked with a challenge-response system. Whenever I perform a request, I receive a code. The code is required in the next request to retrieve the data. The issue I was having, was sending lots of requests in different threads; this could cause a code retrieved in a previous request to become invalid, making an older request for data fail.

I figured that by creating a singleton class responsible for executing requests sequentially, this problem would be fixed (and it did). This singleton class internally uses a FIFO-queue to execute all requests sequentially. I think it was an appropriate solution, especially since this singleton class is used internally, not exposed through interfaces to other classes interacting with my 'framework'.

I use these in objective C, I usually create a data object and stick the networking function in it as well. Some use core data, but I haven't found a need for it yet.

static MySingleton *sharedSingleton;

+ (void)initialize { static BOOL initialized = NO; if(!initialized) { initialized = YES; sharedSingleton = [[MySingleton alloc] init]; } }