Does LiveData retrieved from the Room Database update automatically?-CodePudding

I have a method in my Interface that retrieves all records from my Room Database as a LiveData List. My method is as follows:

 @Query("SELECT *FROM task_table ORDER BY taskId DESC")
    fun getAll():LiveData<List<Task>>

I have the following code in my ViewModel class:

val tasks:LiveData<List<Task>> = taskDao.getAll()

Also I've got an Observer setup in my Fragment as follows:

//After some other code and code to create an instance of the ViewModel
viewModel.tasks.observe(viewLifecycleOwner, Observer {
            it?.let {
                adapter.data = it
            }
        })

I'm a bit confused with LiveData. When I add a new record to my Room Database, my LiveData<List> updates on it's own without me having to call the

getAll() method. When you have LiveData, does the Android OS updates this List when you add/delete/update a record in the Database? Thanks.

CodePudding user response：

When you observe LiveData, you will get the new data as long as the viewLifeCycleOwner is in one of the following states: Lifecycle.State.STARTED or Lifecycle.State.RESUMED. So your assumption is correct.

Please read more about observing LiveData here.

CodePudding user response：

Yes Its obviously updating If you read the documentation then that the observer changes automatically. and update.

CodePudding user response：

STEP 1 @Query("SELECT * FROM Brands order by _id") fun getAll(): List

STEP 2 class BrandViewModel : ViewModel() {

private val _list = MutableLiveData<List<BrandEntity>>().apply {
    value = AppDatabase.get().brandsDao().getAll()
}
val list: LiveData<List<BrandEntity>> = _list

}

STEP 3 val viewModel = ViewModelProvider(this)[ProductsViewModel::class.java] viewModel.list.observe(viewLifecycleOwner) {

}