How to use LiveData into ViewModel in Android

Question

In my application I want to use Viewmodel with LiveData and for this I used this tutorial : ViewModel with LiveData

But I have one question, why used LiveData such as below :

private val _flavor = MutableLiveData<String>("")
val flavor: LiveData<String> = _flavor

fun setFlavor(desiredFlavor: String) {
    _flavor.value = desiredFlavor
}

Why not used with below formed?

val flavor = MutableLiveData<String>()

fun setFlavor(desiredFlavor: String) {
    flavor.value = desiredFlavor
}

Please say me more information about this.

Answer 1

Why not used with below formed ?

val flavor = MutableLiveData<String>()

fun setFlavor(desiredFlavor: String) {
    flavor.value = desiredFlavor
}

In short, it violates encapsulation.

Suppose setFlavor was more complicated:

fun setFlavor(desiredFlavor: String) {
    flavor.value = complextLogicToValidateAndTransform(desiredFlavor)
}

You would always want anything trying to update the flavor to go through setFlavor. But with an exposed MutableLiveData object, anyone can change the flavor and bypass your checks.

viewModel.flavor.setValue(unvalidatedAndUntransformedFlavorThatWillCauseHavok)

By keeping that private and an only exposing a read-only variable, you control how the value can be updated.