#ReactiveSecrets

I really like ReactiveCocoa and started using this framework in nearly all of my projects, however sometimes I had a hard time to find a reactive solution without help for easy looking tasks. Therefore I started this document to collect some use cases I stumbled across during development. This document should serves as a kind of cheat-cheet or as a best practice example collection.

Please note that this is not a pure beginners guide for ReactiveCocoa and requires that you have already read at least Framework Overview, Basic Operators and Design Guidelines

Table of Contents

1. NSNotificationCenter
2. Contributing

NSNotificationCenter

Adjust scrollview when keyboard appears / disappears the reactive way.

NSNotificationCenter.defaultCenter()
	.rac_notifications(UIKeyboardWillShowNotification, object: nil)
	.startWithNext { [weak self] notification in 
		if let keyboardSize = notification.userInfo?[UIKeyboardFrameEndUserInfoKey]?.CGRectValue.size, let weakSelf = self {
			var currentInset = weakSelf.tableView.contentInset
			currentInset.bottom = keyboardSize.height
	   	 	weakSelf.tableView.contentInset = currentInset
	   		weakSelf.tableView.scrollIndicatorInsets = currentInset
	 	}
	}

Be aware, that you have to cancel the subscription when it´s not longer needed. [weak self] or [unowned self] within the closure does not cancel the subscription when e.g. the viewcontroller gets popped or dismissed.

Two possible solutions, as always there are more ways to do that..

1. take care of your disposable

let disposable = NSNotificationCenter.defaultCenter()
	.rac_notifications(UIKey..........

hold a reference to the returned disposable and use disposable.dispose() to cancel the subscription

• (+) very transparent
• (+) manual control of subscription
• (-) requires some boilerplate (e.g. holding reference of disposable)

2. use takeUntil operator in combination with rac_willDeallocSignal

rac_willDeallocSignal works only on NSObject. As another constraint, this operator returns an oldschool RACSignal which must be mapped to an SignalProducer. Time for an extension:

extension NSObject {
	func rac_willDeallocSignalProducer() -> SignalProducer<(), NoError> {
    	return rac_willDeallocSignal()
    		.toSignalProducer()
    		.flatMapError { _ in .empty }
    		.map { _ in () }
	}
}

Then you can do

NSNotificationCenter.defaultCenter()
	.rac_notifications(UIKeyboardWillShowNotification, object: nil)
	.takeUntil(self.rac_willDeallocSignalProducer())

• (+) automatically cancels the subscription when current object deallocs
• (+) no boilerplate (except of optional NSObject extension)
• (-/+) doesn´t work if you have accidently a strong reference to that object (e.g. caused by self caputred within a closure)
• (-) works only with NSObject

Complete solution with takeUntil

NSNotificationCenter.defaultCenter()
	.rac_notifications(UIKeyboardWillShowNotification, object: nil)
	.takeUntil(self.rac_willDeallocSignalProducer())
	.startWithNext { [weak self] notification in 
		if let keyboardSize = notification.userInfo?[UIKeyboardFrameEndUserInfoKey]?.CGRectValue.size, let weakSelf = self {
			var currentInset = weakSelf.tableView.contentInset
			currentInset.bottom = keyboardSize.height
	   	 	weakSelf.tableView.contentInset = currentInset
	   		weakSelf.tableView.scrollIndicatorInsets = currentInset
	 	}
	}

Contributing

If you want to help making this document a useful collection of ReactiveCocoa use cases, add new entries of your daily life reactive development or enhance existing examples 👍🏻

• Fork it
• Create new branch to make your changes / add your stuff
• Commit all your changes to your branch
• Submit a pull request