Delegate

Delegates or Properties, take your pick.

PROPERTIES

Class A (ViewController) wants to communicate with Class B (ViewController)

Before calling Class B, do the following:

In Class B, create a @property NSString* receivedValue;

In Class A,

#import Class B

then in the method that calls B (either prepareForSegue or didSelectRowAtIndexPath or some method where you present Class B view controller, do the following:

Class B *calledVC = alloc/init

calledVC.receivedValue = ‘whatever value you want to pass’;

then call Class B VC

Done!

DELEGATES

Let’s say Class B wants to notify Class A that something has finished.  In Class B add this above your @interface:

@protocol YourDelegateProtocol <NSObject>

- (void)itemWillBePassed;

@end

Then in the regular Class B @interface

@property (nonatomic, weak) id <YourDelegateProtocol> delegate;

This means that Class B has a delegate protocol declared and anyone who wants to be its delegate needs to adopt this protocol and the methods defined herein.

So now in your Class A, right on the @interface line, add <YourDelegateProtocol> right after the:

@interface ViewController : UIViewController

 And since now Class A implements Class B’s protocol, it must implement the delegate methods, which is only itemWillBePassed in our example.

Now simply, whenever Class B needs to notify Class A, it has to call:

[self itemWillBePassed];

And Class A will know about it in its implemented delegate method!