Listen

Simple communication between UIViewControllers / Objects

Why? NSNotificatonCenter works just fine.

• Easier to understand syntax
• Can send messages to one instance, an certain type of object, or all objects
• When listening for messages, you will always know the source of the message (who "said" it)
• Unlike NSNotificationCenter, forgetting to remove observers will not cause an entire object from deallocating (my biggest complaint with NSNotificationCenter)

Installation

Add DataListener.swift and Listenable.swift to your project.

Usage

Conform to the Listenable protocol on the object you want to be able to send / recieve messages.

class ViewController: UIViewController, Listenable{
  //...class implementation
}

You can send messages to every object that has adopted Listenable, every object of a of a certain type, or a particular instance of an object.

Send a message to every Listenable

speak("General", command:"Log", message:json) //json is really anything of type [String:AnyObject]? <--optional

Send a message to every Listenable of a certain type (notice the function name is now "speakTo" instead of "speak")

speakTo("LoginViewController", messageType: "General", command: "DoSomething", message: nil)

The "type" your sending to here is the class name of the object (e.g. "LoginViewController").

Send a message to a particular instance

let secondViewController = SecondViewController() //just for example
speakTo(secondViewController, messageType: "General", command: "Log", message: ["data":"print this out"])

Now you must listen for the messages

Listen's closure always passes in the arguments for speaker (String?), speakerAddr (String?), message ([String:AnyObject]?). They are all optional so you can simply ignore them all or only one's you don't need (e.g. _, _, json in...).

This way, even when you are listening for general messages, you can still tell who sent it. :)

Listen for a message from every Listenable

listen("Authentication", command: "Authentication.Changed") { _ in
    //listening for a message in group "Authentication" with command "Authentication.Changed"
    //also, notice, we are not expecting a message nor do we care about the speaker so we can simply write "_"
    //    for the parameters of the closure
}

Listen for a message from every Listenable of a certain type (again, notice the function name is now "listenTo" instead of "listen")

listenTo("LoginViewController", messageType:"Authentication", command: "Authentication.Changed") { _ in
    //listening for an authentication changed message from the LoginViewController
}

One nice by product of listening to an instance by type is that you can set up a listener for an object before you've even instaniated it...

Example

SettingsViewController could add a listener for NameChangeViewController (e.g. listenTo("NameChangeViewController...)). Now when you change your name, you can speakTo("SettingsViewController"... and pass back the new name.

Listen for a message from a particular instance

listenTo(DataLayer.sharedInstance, messageType:"General", command: "Print"){ (speaker, speakerAddr, json) in
    if json != nil{
        print(json!["realMessage"] as! String)
        print("Sincerly,")
        print("\(speaker!)(\(speakerAddr!))")
    }
}

Now you must stop listening for the messages

You might consider putting this in the deinit() function...

deinit(){
	stopListening()
}

Stop listening to particular messageType and command from a particular instance

stopListeningTo(DataSocket.sharedSocket, messageType: "Authentication", command: "Authentication.Changed")

Stop listening to particular messageType and command from a certain type

stopListeningTo("NameChangeViewController", messageType: "Edit", command: "Name.Changed")

Stop listening to particular messageType and command from every Listenable (notice the function is now "stopListening")

stopListening(messageType: "Authentication", command: "Remote.Identify")

Stop listening for all messages from a particular instance

stopListeningTo(DataLayer.sharedInstance)

Stop listening for all messages from a certain type

stopListeningTo("NameChangeViewController")

Stop listening for ALL messages

stopListening()

Lastly

Performing an action and then listening

Since I was tired of writing code like this...

getNewData()
listen("Data", command: "Update") { _ in
    getNewData()
}

...I decided to write a doListen function (named after a "do-while" loop).

doListen("Data", command: "Update") { _ in
    getNewData()
}

This code will perform getNewData() once and then listen for the Update command before it runs again. doListen also has the usual doListenTo counterparts.

TODOs

• Add Example Project
• Swift 3 support
• Create CocoaPod

Authors

Andrew Goodwin, [email protected]

License

Listen is available under the MIT LICENSE. See the LICENSE file for more info.