UIApplicationDelegate class that separates the different responsibilities into more more reusable classes.

Motivation

UIApplicationDelegate is perhaps the most convoluted protocol in UIKit. A class that conforms to it won't have one single responsibility, hence it violates one of the most important OOP principles: the Single Responsibility Principle (SRP)

The consequence of this is that all the code that we throw in it becomes essentially non-reusable. Our App Delegate becomes often times the most coupled class to your application, and none of the code we write there is easily reusable in another application. However, a lot of the code that we write there should be reusable: handling notifications, state restoration, opening URLs... Ideally we should extract each of these responsibilities into their own class. This is exactly what JSDecoupledAppDelegate allows you to do.

Protocols

JSDecoupledAppDelegate exposes a series of different protocols that each of the classes that will implement one of the responsibilities will conform to:

@protocol JSApplicationStateDelegate;
@protocol JSApplicationDefaultOrientationDelegate;
@protocol JSApplicationBackgroundFetchDelegate;
@protocol JSApplicationRemoteNotificationsDelegate;
@protocol JSApplicationLocalNotificationsDelegate;
@protocol JSApplicationStateRestorationDelegate;
@protocol JSApplicationURLResourceOpeningDelegate;
@protocol JSApplicationShortcutItemDelegate;
@protocol JSApplicationHealthDelegate;
@protocol JSApplicationProtectedDataDelegate;
@protocol JSApplicationWatchInteractionDelegate;
@protocol JSApplicationExtensionDelegate;
@protocol JSApplicationActivityContinuationDelegate;

JSDecoupledAppDelegate has one property for each of these protocols that you have to set with the object that conforms to it. All of the protocols are optional, meaning that you don't have to provide an object unless you want to implement one of the methods.

Check JSDecoupledAppDelegate.h for more details on what methods each of the protocols has.

NOTE: Some of the protocol methods are missing because they're not necessary: whenever there's a corresponding NSNotification that gets sent (specially if the method doesn't have to return anything), it's a better practice to listen for that instead of implementing the method. This allows you to listen to the notification in multiple places vs. implementing all of the logic related to that event in the same method, hence helping you keep responsibilities separate.

Usage

First you must tell UIApplication that it should instantiate an instance of the JSDecoupledAppDelegate class. This happens on the int main() method normally on the main.m file:

return UIApplicationMain(argc, argv, nil, NSStringFromClass([JSDecoupledAppDelegate class]));

After this, all you have to do is to get the instance of the App Delegate and start setting some of its properties.

The only caveat when using JSDecoupledAppDelegate is making sure that you set some of the delegate properties before one of the methods is going to be invoked (e.g. - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions;)

One way of doing this is to implement +load on one of the classes that implements a JSDecoupledAppDelegate delegate protocols and doing something similar to this:

+ (void)load
{
    [JSDecoupledAppDelegate sharedAppDelegate].appStateDelegate = [[self alloc] init];
}

This is why JSDecoupledAppDelegate provides a -sharedAppDelegate method which returns the singleton instance of it. This is to make sure that if this gets called before UIApplication creates the App Delegate, not two instances are created. Also because it doesn't make sense for an application to have more than one App Delegate object.

For more details on this, check the Sample Application in this repo.

Installation

• Using CocoaPods:

Just add this line to your Podfile:

pod 'JSDecoupledAppDelegate', '~> 1.1.0'

• Manually:

Simply add the files JSDecoupledAppDelegate.h and JSDecoupledAppDelegate.m to your project.

Compatibility

JSDecoupledAppDelegate is compatible with iOS 5, iOS 6, iOS 7 and iOS 8.

License

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