Swift Property Value Monitoring

You must be familiar with the observer pattern in object-c. Swift provides a simpler way to implement

When we need to assign values to the object's property values, we can use Willset and didset to observe the changes in the object's property values.

Let's look directly at an example. Create a class Student to monitor the property name

The first is the definition of the student class.

Class student{    init (name:string) {        username=name;    }        var username:string= "" {        willset{            println ("Student name Newvalue:\ (newvalue)")        }        didset{            println ("Student name Oldvalue:\ (oldValue)")}}            

And then we initialize the student and modify his username to try the effect.

  var student=student (name: "Zhang San")//Note that the time of initialization is        student.username= "Lisi" without invoking the monitoring method

Printing results are as follows

Student name Newvalue:lisi

Student name OldValue: Zhang San

It's easy, there's a problem to keep talking about.

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Swift Property Value Monitoring