Calling method in current view controller from App Delegate in iOS

Question

I have two view controllers (BuildingsViewController and RoomsViewController) that both use a function within the App Delegate called upload. The upload function basically d

Answer 1

Step 1:

In your App Delegate .h file you need to declare a protocol like so:

@protocol AppConnectionDelegate 
@required
   -(void)connectionFinished:(NSObject*)outObject;
@end

In the same file, add an ivar like so:

id *delegate;

Declare the ivar as a property:

@property (nonatomic, assign) id delegate;

In the App Delegate .m file, synthesize the ivar:

@synthesize delegate;

In the App Delegate .m file, on connectionDidFinishLoading do:

if([self.delegate respondsToSelector:@selector(connectionFinished:)])
{
   [self.delegate connectionFinished:objectYouWantToSend];
}

---

In your viewcontroller's .h file, implement the AppConnectionDelegate by importing a reference to the app delegate file:

#import "AppDelegate_iPhone.h" //if using iPhone
#import "AppDelegate_iPad.h" //if using iPad

In the same file, at the end of the first line of the interface declaration do:

@interface AppDelegate_iPhone : AppDelegate_Shared 

Declare ivars accordingly:

AppDelegate_iPhone *appDelegate; //if using iPhone
AppDelegate_iPad *appDelegate; // if using iPad

In your viewcontroller's .m file in the viewDidLoad(), get a reference to your app delegate using:

If iPhone;

appDelegate = (AppDelegate_iPhone*)[[UIApplication sharedApplication] delegate];

If iPad:

appDelegate = (AppDelegate_iPad*)[[UIApplication sharedApplication] delegate];

Then set the viewcontroller to be the delegate in viewDidLoad() by doing:

appDelegate.delegate = self;

Now you need to simply implement the connectionFinished method in the .m file:

- (void)connectionFinished:(NSObject*)incomingObject
{
//Do whatever you want here when the connection is finished. IncomingObject is the object that the app delegate sent.
}

Now whenever your app delegate's connectionDidFinishLoading is called, the view controller will be notified.

[It's a best practice to set appDelegate.delegate = nil if you're done using the connectionFinished callback]

This is tried and tested. If you have questions, leave a comment......

--EDIT--
This is a robust alternative to NSNotification. I use both depending on the requirements. The process I use to decide between using NSNotification or a delegate callback using a protocol is simply:

For notifications:
One sender, multiple listeners.
No reference possible between sender and listener.
Complex/multiple objects need not be sent

For delegate callbacks using protocols:
One sender, limited (usually 1) listeners.
A reference between sender and listener is possible.
Complex/multiple objects are to be sent (for example, response objects that need to be sent)

I know sending objects is possible through notifications but I prefer protocols for that.
--EDIT--