当新值与上一个值相同时，StateFlow 不会发出

Question

I have a login form. I use StateFlow to send LoginResult (after call API) from ViewModel to Activity . In the Activity, I will show an error dialog if login failed.
It works well for the first time but from the second time I login failed, the error dialog won't show again. I tested both .value and .emit on StateFlow

private val _loginResult = MutableStateFlow(LoginResult())
val loginResult: StateFlow<LoginResult> = _loginResult

fun login(email: String, password: String) {
    viewModelScope.launch {
        when (val result = loginRepository.login(email, password)) {
            is Result.Fail-> {
                _loginResult.value = LoginResult(error = "Login failed")
                // _loginResult.emit(LoginResult(error = "Login failed")) same issue
            }
            ...
       }
   }
}

Answer 1

For this case, I use SharedFlow so my Activity still able to collect the new value even it same the last value

private val _loginResult = MutableSharedFlow<LoginResult>()
val loginResult: SharedFlow<LoginResult> = _loginResult

...
_loginResult.emit(LoginResult(error = "Login failed"))

Another possible solution but it's not good is change my current data class LoginResult(...) to class LoginResult . Then every new instance of LoginResult will different

Answer 2

That's by default. What you could do is to emit one value when the login is in progress, before emitting the result. That way you would have a sequence like:

in_progress -> error -> in_progress -> error

Apps usually display a spinner or something when the in_progress or loading or whatever is emitted.