hey how can i wait for a result in `coroutine` . I...

# coroutines

[Harpreet Singh.8052]

hey how can i wait for a result in coroutine . I have a method to store image to firebase and return its URL , it s suspend function and i am calling that ImageUpload() method inside my view model

var imageUri = mutableStateOf<String?>(null)

fun uploadImage(uri: Uri) {
        viewModelScope.launch {
            imageUri.value = saveUserRepositoryImp.saveImageToFirebase(uri)
        }
        _userDetail = _userDetail?.copy(
            profileUri = imageUri.value
        )
    }

this is function inside my viewmodel and this function is called inside viewModelScope.launch{ uploadImage(uri) } i want it to wait for the result because i want show loading and when result is return the loading should be stop

[streetsofboston]

You should not 'wait' in your UI for loading to finish.

fun uploadImage(uri: URI) {
  _uiState.value = UiState.Loading // will show Loading... on your UI
  viewModelScope.launch { 
      _uiState.value.userDetail = _uiState.value.userDetail?.copy(profileUri = saveUserRepositoryImp.saveImageToFirebase(uri));
  }
}

[streetsofboston]

Your UI code will collect/subscribe-to the viewModel.uiState,
When it sees a UiState.Loading, then it shows a Loading.... screen/spinner/view
When later the UiState.UserDetail is observed, it shows you the upload-result/user-details.

[streetsofboston]

If you don't use streams/flows in your UI, then you can make uploadImage suspending:
In your UI:

...
showLoadingView()
result = uploadImage(imageUri)
showResult(result)
...

In your view model:

suspend fun uploadImage(uri: URI) {
  return withContext(Dispatchers.IO) { 
    saveUserRepositoryImp.saveImageToFirebase(uri));
  }
}

(but I suggest using an MVVM pattern where your UI observes Flow(s) from your ViewModel)

[streetsofboston]

(the code-snippets may not compile correctly.... consider them as pseudo-code 🙂 )

[Harpreet Singh.8052]

im using mvvm the actul code is in remote then to repository then to viewmodel

[Harpreet Singh.8052]

because calling mehod inside viewmodelscop.launc it suddely executs the next line and assign it default value , i want it to wait

[streetsofboston]

Ah... I see... you'll have to put the assignment to _userDetail inside the launch...

[Harpreet Singh.8052]

actual imp

override suspend fun saveImageToFirebase(uri : Uri)  : String {

    var imageUri : String = ""

    Log.d("debug", "uploadImage1")

        storageReference.child(FirebaseAuth.getInstance().uid!!).putFile(uri)
            .addOnSuccessListener {
                storageReference.child(FirebaseAuth.getInstance().uid!!).downloadUrl.addOnSuccessListener { uri ->
                    imageUri = uri.toString()
                    Log.d("debug", "uploadImage2:  ${uri}")
                }
            }
            .addOnFailureListener{
                Log.d("debug", "uploadImage3:  ${it.message}")
                it.printStackTrace()
                Log.d("debug", "uploadImage4:  ${it.message}")
            }

    return imageUri
}

the repo

override suspend fun saveImageToFirebase(uri: Uri) : String {
   return userDetailService.saveImageToFirebase(uri)
}

viewmodel

fun uploadImage(uri: Uri) {
    viewModelScope.launch {
           Log.d("debug", "uploadImage: actual 1")
           val profileUri = saveUserRepositoryImp.saveImageToFirebase(uri)
           Log.d("debug", "uploadImage: actual 2-> ${profileUri}")
    }
}

[streetsofboston]

Looks good, but you'll need an assignment to the flow.value inside your viewModelScope.launch with the profileUri result

[Harpreet Singh.8052]

here in viewmodel im getting Log.d("debug", "uploadImage: actual 2-> ${profileUri}") im getting empty string because imreturn empty sting in my actual implemt var imageUri : String = ""

[streetsofboston]

fun uploadImage(uri: Uri) {
    uiState.value = UiState.Loading
    viewModelScope.launch {
           Log.d("debug", "uploadImage: actual 1")
           val profileUri = saveUserRepositoryImp.saveImageToFirebase(uri)
           uiState.value = UserDetails(profileUri)
           Log.d("debug", "uploadImage: actual 2-> ${profileUri}")
    }
}

^^^ or something similar... the uiState is a Flow<UiState> here, where UiState a sealed class/interface that can have a Loading value or a UserDetails instance.

[streetsofboston]

The empty string is an issue with your repo/service code...

[streetsofboston]

It doesn't wait for the callback to return a result

[Harpreet Singh.8052]

yes , it dosent wait and return empty , previousey i assign a default value to null but then it return null

[Harpreet Singh.8052]

can i add withcontext n my actul implemt so that it can wait for the result

[streetsofboston]

override suspend fun saveImageToFirebase(uri : Uri)  : String {
    return suspendCancellableCoroutine { cont->
        storageReference.child(FirebaseAuth.getInstance().uid!!).putFile(uri)
            .addOnSuccessListener {
                storageReference.child(FirebaseAuth.getInstance().uid!!).downloadUrl.addOnSuccessListener { uri ->
                    imageUri = uri.toString()
                    cont.resume(imageUri)
                }
            }
            .addOnFailureListener{
                cont.resumeWithException(it)
            }
    
        cont.invokeOnCancellation { /* deregister your onSuccess and onFailure listeners here */ }    
    }
}

[streetsofboston]

https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines/suspend-cancellable-coroutine.html

[Harpreet Singh.8052]

thanks man ! the actual problem is only thing i know about coroutine is If you want to perform a task asynchronously , you can mark the function as suspend and call it inside a coroutine scope. i need to dive more into it , can u suggest some topics or resources , thanks