ViewModel 支持属性 [kotlin]

Question

Looking to the code of some Google's demo app (like sunflower or Google io 2018 app) and I've noticed that for the viemodels' backing properties they use a separate instance of the same type with a custom getter; like this:

private val _userData: MutableLiveData<User>
val userData: LiveData<User>
    get() = _userData

but why do they do that? Isn't better to directly make the _userData accessible? Could it be because while _userData is a MutableLiveData they don't want the observer to be able to change the value?

Answer 1

userData which is exposed to the Activity or Fragment must be immutable since the view only needs to observe to the LiveData . So, we need to make the actual _userData returns a LiveData .

One way is using the Kotlin coding convention and create two variables, _userData and userData , one is mutable and another one is not:

If a class has two properties which are conceptually the same but one is part of a public API and another is an implementation detail, use an underscore as the prefix for the name of the private property.