local_broadcast_receiver.md

LocalBroadcastReceiver implementation in iOS

I was recently looking for a way to pass data from the background to the user interface. In android, we can use localBroadcastReceiver. But in iOS how do we implement this, especially in Swift 4?

Step 1: Initiating the message from the background

In order to send the message We will be using the helper class NotificationCenter

/*  This is the data object we can pass to the UI  */
let dataToSend = ["data" : "Sending message from backend"]
NotificationCenter.default.post(name: Notification.Name(rawValue: "{key_to_identify_the_messae}"), 
                                object: nil, 
                                userInfo: dataToSend)

Step 2: Receiving the message in the UI

To get the messages for that specific key we need to subscribe to the NotificationCenter.

• Inside the viewDidAppear method in our ViewController, we can register our subscriber for the specified key.
• We also specify a selector to have a function to handle when the message is received.

NotificationCenter.default.addObserver(self, selector: #selector(handleNotification(withNotification:)),
      name: NSNotification.Name(rawValue:"notification_key"), object: nil)

• We can get the message we passed from the background in the declared function:

@objc func handleNotification(withNotification notification : NSNotification) {
  let data = notification.userInfo?["data"]
}