When to use MutableLiveData and LiveData

Question

when to use MutableLiveData and LiveData means the area of using the methods :

MutableLiveData<User> getUser() {     if (userMutableLiveData == null) {         userMutableLiveData = new MutableLiveData<>();     }     return userMutableLiveData; } 

and when to use this,

LiveData<User> getUser() {     if (userMutableLiveData == null) {         userMutableLiveData = new MutableLiveData<>();     }     return userMutableLiveData } 

Answer 1

LiveData has no public method to modify its data.

LiveData<User> getUser() {     if (userMutableLiveData == null) {         userMutableLiveData = new MutableLiveData<>();     }     return userMutableLiveData } 

You can't update its value like getUser().setValue(userObject) or getUser().postValue(userObject)

So when you don't want your data to be modified use LiveData If you want to modify your data later use MutableLiveData

Answer 2

Let's say you're following MVVM architecture and having LiveData as observable pattern from ViewModel to your Activity. So that you can make your variable as LiveData object exposing to Activity like below :

class MyViewModel : ViewModel() {     // LiveData object as following     var someLiveData: LiveData<Any> = MutableLiveData()      fun changeItsValue(someValue: Any) {         (someLiveData as? MutableLiveData)?.value = someValue     } } 

And now at Activity part, you can observe LiveData but for modification you can call method from ViewModel like below :

class SomeActivity : AppCompatActivity() {     // Inside onCreateMethod of activity     val viewModel = ViewModelProviders.of(this)[MyViewModel::class.java]     viewModel.someLiveData.observe(this, Observer{         // Here we observe livedata     })     viewModel.changeItsValue(someValue) // We call it to change value to LiveData     // End of onCreate }