Question

I create new tabbed view project in xcode, in appdelegate I created a protocol

.h file

@protocol myProtocol <NSObject>
-(void)myProtocolMethodOne;
@end
.
.
.
@property (weak) id<myProtocol> mypDelegate;

.m file

@synthesize mypDelegate;
.
.
.
//Inside didFinishLaunchingWithOptions
[mypDelegate myProtocolMethodOne];

In firstViewController & secondViewController (both are displayed as two different tab) I did this in both

AppDelegate *ad = (AppDelegate*)[[UIApplication sharedApplication]delegate];
    [ad setMypDelegate:self];
.
.
.
-(void)myProtocolMethodOne
{
    NSLog(@"1st VC");
    [[self tabBarItem]setBadgeValue:@"ok"];
}

The code is working perfectly but only secondViewController is responding.

I am looking for a broadcasting and listener kind of mechanism using delegates not notifications.

I searched a lot but did find any solutions except this but code is advance for me to understand, so I am taking a step by step approach to understand this by starting form a simple project. Please help me regarding this. How both viewcontrollers can respond to delegate at same time, what should I do?

Answer 1

In your case is enough to hold an array with all delegates, by holding an array of delegates, possibly as a private property, and allowing to add/remove delegates:

@interface AppDelegate() // .h file

@property (nonatomic,strong,readwrite) NSMutableArray* delegates;

@end 

// .m file

- (void) addDelegate: (id<MyProtocol>) delegate // By convention the first letter should be capital.
{
    // Optional code you may need to execute before adding it.
    [delegates addObject: delegate];
}

I leave to you the removeDelegate method, it’s very simple to implement.

How to call the delegates methods

It’s enough to call the selector on every object:

[delegates makeObjectsPerformSelector: myProtocolMethodOne];

If you need to take return values it’s better to do it this way:

NSMutableArray* returnValues= [NSMutableArray new];
for(id<MyProtocol> delegate in delegates)
{
    id result= [delegate myProtocolMethodTwo]; // Method returning a value
    [returnValues addObject: result];
} 

How to add the delegates

In every controller (up to N times) you should be able to add it:

AppDelegate *ad = (AppDelegate*)[[UIApplication sharedApplication]delegate];
[ad addDelegate:self];

Additional problem: You may want to have weak delegates, but a NSArray holds strong references. Here you can find a nice solution for this:

NSArray of weak references (__unsafe_unretained) to objects under ARC

It basically says to use NSValue to store weak reference using the valueWithNonretainedObject method.