Following the codelab demo from Google (link), I try to refactor my code to ViewModel + coroutines. My question is, instead of just insert the data (original code), I want to wait for the result from the inserting operation, which should return the id if the inserting succeeded, then do something based on the result. So how to do it?
Currently, I send a method to the ViewModel insert method as a callback. Of course, observing the ViewModel is another option. But is there any better solution?
My current code:
EventActivity:
viewModel.insert(Event("name"), {
if (it == -1L) {
Log.i("insert", "failure")
} else {
Log.i("insert", "success: $it")
}
})
EventViewModel:
private val mEventDao: EventDao = AppDatabase.getDatabase(application).eventDao()
private val mJob = Job()
private val mScope = CoroutineScope(Dispatchers.Main + mJob)
fun insert(event: Event, callback: (id: Long) -> Unit) {
mScope.launch(Dispatchers.IO) {
val result =
try {
// just for testing delay situation
delay(5000)
val id = mEventDao.insertEvent(event)
id
} catch (e: Exception) {
-1L
}
withContext(Dispatchers.Main) {
callback(result)
}
}
}
EventDao:
@Dao
interface EventDao {
fun insertEvent(event: Event): Long
}
You can add a LiveData object to EventViewModel, update it when inserting is done and subscribe to it in Activity:
class EventViewModel : ViewModel() {
//...
var insertionId = MutableLiveData<Long>()
fun insert(event: String) {
mScope.launch(Dispatchers.IO) {
val result =
try {
// just for testing delay situation
delay(5000)
val id = mEventDao.insertEvent(event)
id
} catch (e: Exception) {
-1L
}
insertionId.postValue(result)
}
}
}
And subscribe in the EventActivity:
class EventActivity : AppCompatActivity() {
lateinit var viewModel: EventViewModel
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
viewModel = ViewModelProviders.of(this).get(EventViewModel::class.java)
viewModel.insertionId.observe(this, android.arch.lifecycle.Observer { id ->
// Use `id` for example to update UI.
})
// ...
viewModel.insert(Event("name"))
}
}
suspend fun insert(data: String): String = suspendCoroutine { cont ->
//put logic here
cont.resume("Done")
//if error use this
cont.resumeWithException(Exception("Error"))
}
i can remove callback in this function with return and wait the return
fun insertData(){
GlobalScope.launch {
val status = insert("This is Data!")
if( status == "Done"){
}else{
}
}
}
But is there any better solution?
i think there is.
in androidx.lifecycle.*:2.2.0 alpha01 the
liveData { . . . } , emit() functions are available.
you can rewrite your code in viewModel like this.
fun insertData(event: String) = liveData {
val id = mEventDao.insertEvent(event)
emit(id)
}
and in your activity observe it.
viewModel.insertData("YourEvent").observe(this) {
updateUi(id)
}
don't forget to change your Dao methods to suspend
@Dao
interface EventDao {
suspend fun insertEvent(event: Event): Long
}
BTW at this time the latest version of live data is 2.2.0-rc03
implementation "androidx.lifecycle:lifecycle-livedata-ktx:2.2.0-rc03"
you can see better implementation in android documentation : Use coroutines with LiveData