Cfrgtkky

I am not able to get the idea of MediatorLiveData while working with LiveData. In documentation it is mentioned that MediatorLiveData is a subclass of LiveData that will observe LiveData and react on onChanged method. My question is what's it's difference from having a function in observe of LiveData and do something with data if the new data is different?

For example, let's say I have query from Room Database that returns LiveData as below

@Query(“SELECT * FROM Users WHERE userid = :id”)

fun getUserById(id: String): LiveData<User>

If I want to use MediatorLiveData, I can have an extension as below

fun <T> LiveData<T>.distinctUntilChanged(): LiveData<T>{

    var lastValue: Any? = Any()

    return MediatorLiveData<T>().apply {

        addSource(this@distinctUntilChanged){

            if (it != lastValue){

                lastValue = it

                postValue(it)

            }

        }

    }

}

And then use it in my Activity as

userDao.getUserById("someId").distinctUntilChanged()

    .observe(this, user -> {/*Do something with user*/})

Contrary to above scenario, I can just have a wrapper function inside observe method as below

var lastUser = null

userDao.getUserById("someId")

    .observe(this, user -> {

        if (lastUser != user){

            lastUser = user

            /*Do something with user*/

        }

    })

Can anyone elaborate why I should use MediatorLiveData instead of just having simple check?