Question

Inside ClassA:

-(void)authenticateUser
{
   authenticate_Obj = [classB_Obj authenticateMobileUser];
}

Inside ClassB:

-(AuthenticateObj*)authenticateMobileUser
{
   [mobile_Obj AuthenticateMobileServer:self action:@selector(Handler:)];
   return authenticate_G_Obj;
}

-(void)Handler:(id)value
{
   authenticate_G_Obj = (AuthenticateObj*)value;
}

Now once the authenticateMobileUser method of classB returns the controll back to ClassA, we will get the Object authenticate_Obj initiated.

My problem is , when i run the project the authenticate_Obj is NULL… actually when it enters the handler method , the Object is initiallized. but the controlled is returned back to ClassA, without entering into Handler method. I guess this is the problem of Asynchronous execution.
How to make it enter into handler method and then only return the controll to ClassA??

Plz help me..

Thank You.

Answer 1

It sounds like what you think you want to do is to block execution until authentication completes. This might be possible if AuthenticateMobileServer spawns a background thread to work in — you’d use a synchronisation object such as NSLock — but it’s really a Bad Idea. Why have a background thread at all if you’re going to block anyway? And thread synchronisation is notoriously tricky and prone to errors if you don’t know what you’re doing, which (let’s face it) you don’t.

Instead, you probably should accept that there will be a period of uncertainty while the authentication takes place, during which your app should keep processing in some intermediate state, and then use a callback to notify you when the authentication is complete and you can then go on with whatever it is you need to do with the authenticated user.

There are a bunch of ways you could do this, and there’s not enough detail in the question to say exactly which would be best. But you already seem to be using something very similar within ClassB, so I’d say do the same from ClassA:

Inside ClassA:

-(void)authenticateUser
{
   authenticate_Obj = nil;
   [classB_Obj authenticateMobileUserAndNotify:self action:@selector(authenticatedObject:)];
   // returns more or less immediately, not yet authenticated
}

-(void)authenticatedObject:(YourAuthObjectClass*) authObj
{
    authenticate_Obj = authObj;
    // do post-authentication stuff here
}

Inside ClassB:

-(void)authenticateMobileUserAndNotify:(id)target action:(SEL)sel
{
   // I'm making these ivars for simplicity, there might be other considerations though
   callbackTarget = target;
   callbackSelector = sel;

   [mobile_Obj AuthenticateMobileServer:self action:@selector(Handler:)];
}

-(void)Handler:(id)value
{
   authenticate_G_Obj = (AuthenticateObj*)value;
   [callbackTarget performSelectorOnMainThread:callbackSelector withObject:authenticate_G_Obj waitUntilDone:NO];
}

Obviously this is just a sketch and not intended to be used as is. And you’ll need to consider what goes on in your app while in the waiting state, with authentication in progress but authenticate_Obj still nil. But hopefully you get the idea.