Signalling a facebook async request has finished - ios

Question

I have some code which queries facebook for information
if (FBSession.activeSession.isOpen) {
[[FBRequest requestForMe] startWithCompletionHandler:
^(FBRequestConnection *connection,
NSDictionary<FBGraphUser> *user,
NSError *error,) {
if (!error) {
//populate the **mUser** with data
} else {
NSLog(#"Facebook error encountered: %#", error);
}
}];
} else {
NSLog(#"Facebook session is closed");
}
My question is, what is the best way to tell the caller of the function that facebook is finished? I can't simply return from inside the block (incompatible block pointer types).
The calling code looks like this:
myfacey *fb = [[myfacey alloc] init];
[fb getUserFromFacebook: mUser];
//Need to access a populated mUser object here
//calls to mUser result in nil values because facebook hasn't finished
If facebook accessed things synchronously I would have no problem, because mUser would have valid data in it.
Since I have to make asynch calls, what is the best way to signal the calling class that facebook is done populating the variable?

Answer 1

The best way to continue with your program once the asynchronous method has been finished, is putting this code into the completion handler.
Don't try to "return", just "continue" the program in the completion handler.
You should just care about the "execution context" (say thread or dispatch queue) on which the completion handler will be invoked from the async method: if this is not explicitly documented, the completion handler may be called on any thread. So, you might want to dispatch explicitly to the main thread - if necessary:
if (FBSession.activeSession.isOpen) {
[[FBRequest requestForMe] startWithCompletionHandler:
^(FBRequestConnection *connection,
NSDictionary<FBGraphUser> *user,
NSError *error,) {
if (!error) {
// Continue here with your program.
...
// If you need ensure your code executes on the main thread:
dispatch_async(dispatch_get_main_queue(), ^{
// continue with your program on the main thread, for example:
// populate the **mUser** with data
[self.tableView reloadData];
...
})
} else {
NSLog(#"Facebook error encountered: %#", error);
}
}];
} else {
NSLog(#"Facebook session is closed");
}