Notification mechanism simplified (swift)

The aim of this post is to explain and provide an example about notification mechanism simplified (,but not simplistic) in swift. The first thing that you need to be clear is when to use this mechanism and when delegate mechanism.

Both mechanism help to decouple view controllers. Notifications offer the advantage that multiple objects can observer one notifications.  In delegate mechanism the communication is direct (through a protocol method implementation) with the delegate class.

The example that I am going to present to shows the notification mechanism as a broadcast service. A timer periodically will launch a notification, on the other side there will be two classes (Alice and Bob) that will be intercepting the message.

As you can see in the code every 3 seconds is sent a notification that is intercepted by Alice and Bob class in the following way:

Is important to keep under control when to unsubscribe to the notification mechanism. In case of Alice is after receiving 3 messages and in case of Bob is when the class is removed from memory.

Once we run the project we should have to see the following in the log window:


You can find the sample project here.






Key-Value Observing mechanism simplified

The aim of this post is to show how it works Key-Value Observing mechanism (KVO). KVO is a mechanism for transparently notifying observers of changes in object properties. In other words,  this mechanism will allow us to trap when some object property value is being modified.


We will create a class that will hold the property to be observed:

Its implementation is the following:

As you can see the property is set to 3 in the class initialiser. Now we are going to implement the KVO mechanism in the ViewController. We will add the observer in the viewDidLoad Method:

As important as setup the observer is remove it when it is not necessary, I will add it in the dealloc method:

In the viewWillAppear method I will update property that is being observed:

The callback that is being called every time that the property is changed is the following:

When you will run the project you will see that the above function is called twice. Once during NewObject initialisation and the other during viewDidAppear.


And in the log screen:

You can download the code from here.