我从不进入我的 ViewModel 中的 LiveDataScope

Question

我开发了2个登录功能。

当我使用 ViewModel 范围时，第一个“loginOne”有效。

另一个在我使用 LiveData 范围时不起作用。

你有想法吗？我想让“loginTwo”工作。

API

interface LoginAPI {

    @POST("login")
    suspend fun getUser(@Body loginRequest: LoginRequest): User
}

存储库

class LoginRepository(private val loginAPI: LoginAPI) {

    suspend fun getUser(loginRequest: LoginRequest) = loginAPI.getUser(loginRequest)
}

ViewModel

class LoginViewModel(private val loginRepository: LoginRepository) : ViewModel() {

    private var user: LiveData<User>? = null

    fun loginOne(username: String, password: String) {
        viewModelScope.launch {
            // i can enter here and get the user :)
            val user = loginRepository.getUser(LoginRequest(username, password))
            user
        }
    }

    fun loginTwo(username: String, password: String) {
        user = liveData(Dispatchers.IO) {
            // i never enter inside.. why ?
            val user = loginRepository.getUser(LoginRequest(username, password))
            emit(user)
        }
    }

    fun getUser(): LiveData<User>? = user
}

Fragment，我的viewModel注入了Koin

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
   super.onViewCreated(view, savedInstanceState)

   loginViewModel.getUser()?.observe(this, Observer { user ->
       Log.d(LoginFragment::class.java.name, "User : $user ")
   })

   loginViewModel.loginOne("user","pcw123")
   loginViewModel.loginTwo("user","pcw123")
}

Answer 1

确保您以正确的方式创建了 Scope。此外，您正在使用适当的 Dispatchers 来获得想要的结果。

您还可以检查调用是否在您想 postValue 时执行。检查 Job 是否还活着。

检查这个 thing。你的 emmit 电话看起来很可疑。

When using LiveData, you might need to calculate values asynchronously. For example, you might want to retrieve a user's preferences and serve them to your UI. In these cases, you can use the liveData builder function to call a suspend function, serving the result as a LiveData object.

Each emit() call suspends the execution of the block until the LiveData value is set on the main thread.

In the example below, loadUser() is a suspend function declared elsewhere. Use the liveData builder function to call loadUser() asynchronously, and then use emit() to emit the result:

val user: LiveData<User> = liveData {
    val data = database.loadUser() // loadUser is a suspend function.
    emit(data)
}

编辑： MutableLiveData 用于 user 变量 - 解决了问题。

Answer 2

来自文档：

The liveData building block serves as a structured concurrency primitive between coroutines and LiveData. The code block starts executing when LiveData becomes active and is automatically canceled after a configurable timeout when the LiveData becomes inactive.

因此，在您的情况下，当您从片段中观察时，'user' liveData 已经激活。因为您在观察到 liveData 后调用了 loginTwo()，所以不会再触发 emit 函数。在观察 liveData 之前尝试调用 loginTwo() 以从 liveData ktx 获取发射值。

我从不进入我的 ViewModel 中的 LiveDataScope

I never enter inside the LiveDataScope inside my ViewModel

android

viewmodel

kotlin

android-livedata

kotlin-coroutines