ios - Facebook API - How to cancel Graph Request

Question

I occasionally need to cancel a FaceBook graph request, but there seems to be no cancel or similar method in their API to do so. At the moment, crashes sometimes occur as the delegate I assigned to the request has been deallocated. Is there any way to cancel a graph request once submitted please?

Answer 1

I'm assuming you're talking about the facebook-ios-sdk project, and the lack of a cancel method in Facebook.h. I noticed this as well, and eventually decided to add my own cancel method. Just to note, the delegate you assign to the request shouldn't ever be dealloc'd and then referenced, because the request retains the delegate. See this similar question. Now, if you find yourself really needing a cancel method for some other reason...

Adding a cancel method:
Facebook requests are made in an opaque manner. You never see them, and only hear about results via the Facebook class. Under the hood, the Facebook class makes Graph API requests with the (not for public use) FBRequest class. This class is is basically a fancy NSURLConnection delegate. So to cancel the request, the member NSURLConnection just has to be told to cancel. Adding this method to FBRequest:

// Add to FBRequest.h
- (void)cancel;

And...

// Add to FBRequest.m
- (void)cancel {
    [_connection cancel];
    [_connection release], _connection = nil;
}

Now, to expose an interface in the Facebook class to make use of the new method...

// Add to Facebook.h
- (void)cancelPendingRequest;  

And...

// Add to Facebook.m
- (void)cancelPendingRequest {
    [_request cancel];
    [_request release], _request = nil;
}

That's all there is to it. The method above will cancel the most recent request, and you'll never hear from it again.