Question

How can I make a viewcontroller singleton, to then use this code:

FacebookManager *manager = [FacebookManager sharedManager];
[manager openSessionWithAllowLoginUI:NO]

??

Answer 1

That’s not necessarily a singleton. A singleton can only have one instance at any given time. Shared instances are similar, but don’t prevent additional instances from being created.

You can implement a shared instance with a static variable and a class method like this:

+ (FacebookManager *)sharedManager
{
    static FacebookManager *shaderManager = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        shaderManager = [[FacebookManager alloc] init];
    });
    return shaderManager;
}

Don’t forget to declare the class method in your header.