Inter-process signaling with addressable receivers using the Darwin notification center.

See Releases for a high-level overview of recent updates.

The example in this repo contains an iPhone app, a Today widget and a WatchKit extension that exchange signals by using CCHDarwinNotificationCenter. To see the updates, start at least two processes such as the WatchKit app and the iPhone app.

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Installation

Use CocoaPods to integrate CCHDarwinNotificationCenter into your project. Minimum deployment targets are 7.0 for iOS and 10.9 for OS X.

platform :ios, '7.0'
pod "CCHDarwinNotificationCenter"

platform :osx, '10.9'
pod "CCHDarwinNotificationCenter"

Sending notifications across process boundaries

The Darwin notification center is a system mechanism on iOS and OS X to send signals across process boundaries. It's useful to exchange information between two or more running processes such as an iPhone app notifying a WatchKit Extension that new data has arrived.

A Darwin notification is a signal only; it can't transport any data apart from the notification identifier. If you need to share data across processes, you can set up an app group, which allows you to exchange data via APIs such as NSUserDefaults and Core Data.

Darwin notifications don’t need an app group or any other setup to work. Because the notification namespace is shared across all applications in the system, Apple recommends a reverse-DNS-style naming, for example "com.example.MyMessage".

CCHDarwinNotificationCenter simplifies handling Darwin notifications by:

• Providing a simple API to send Darwin notifications with one line of code
• Converting incoming Darwin notifications into notifications that can be received with the NSNotificationCenter API
• Mangling notification identifier strings to receive notifications from specific endpoints.

Simple Darwin notification API

To send Darwin notifications use:

    CCHDarwinNotificationCenter.postNotificationWithIdentifier("com.example.MyMessage")

To receive Darwin notifications, first start converting them into NSNotifications:

    CCHDarwinNotificationCenter.startForwardingDarwinNotificationsWithIdentifier("com.example.MyMessage")

Then receive the converted signals via the NSNotificationCenter API:

    NSNotificationCenter.defaultCenter().addObserver(self, selector: "notificationDidReceive", name:"com.example.MyMessage", object: nil)

    func notificationDidReceive() {
        println("notificationDidReceive")
    }

Addressing endpoints

Darwin notifications have the downside of being received by the process of the sender as well. If you have an iPhone app, a Today widget and a WatchKit extension, sending a notification with the same identifier makes it hard to know where the signal came from.

For this reason, CCHDarwinNotificationCenter offers an API that appends a process specific string to the notification identifier. This appendix is then used to filter out messages you don't need. The API is as follows:

    CCHDarwinNotificationCenter.startForwardingNotificationsWithIdentifier("com.example.MyMessage", fromEndpoints: .Default)
    CCHDarwinNotificationCenter.stopForwardingNotificationsWithIdentifier("com.example.MyMessage", fromEndpoints: .Default)
    CCHDarwinNotificationCenter.postNotificationWithIdentifier("com.example.MyMessage")

Note that this API does not include the word "Darwin" in its methods. The endpoint mask allows you to filter messages where .Default means all messages except the ones sent by your own process.