以正确的方式使用协程

Question

我是第一次实现协程。我正在遵循简单登录应用程序的 MVP 模式。这是我的业务流程 -

单击的登录按钮将遵循此方向 -

LoginFragment ->

LoginPresenter -> Repository -> API repository -> RetrofitInterface

登录响应将遵循以下方向 -

RetrofitInterface -> API repository -> repository -> LoginPresenter -> LoginFragment

这是代码 -

RetrofitInterface.kt

@POST("login")
    fun loginAPI(@Body loginRequest: LoginRequest): Deferred<LoginResponse>?

这是我的结果.kt

sealed class Result<out T : Any> {
    class Success<out T : Any>(val data: T) : Result<T>()
    class Error(val exception: Throwable, val message: String = exception.localizedMessage) : Result<Nothing>()
}

APIRepository.kt

override suspend fun loginAPICall(loginRequest: LoginRequest) : Result<LoginResponse>? {
        try {
            val loginResponse = apiInterface?.loginAPI(loginRequest)?.await()
            return Result.Success<LoginResponse>(loginResponse!!)
        } catch (e : HttpException) {
            return Result.Error(e)
        } catch (e : Throwable) {
            return Result.Error(e)
        }
    }

Repository.kt

override suspend fun loginUser(loginRequest: LoginRequest): Result<LoginResponse> {
        if (isInternetPresent(context)) {
            val result = apiRepositoryInterface?.loginAPICall(loginRequest)
            if (result is Result.Success<LoginResponse>) {
                val loginData = result.data
                cache?.storeData(loginData)
            }
            return result!!
        } else {
            return Result.Error(Exception())
        }
    }

现在如何在演示器中启动协程？我需要在后台线程上执行此 API 调用并在 UI 线程上发布结果？

Answer 1

您需要

使用本地作用域和注入CoroutineContext在演示器中启动协程才能更改它，例如在单元测试中：

class Presenter(
    private val repo: Repository,
    private val uiContext: CoroutineContext = Dispatchers.Main
) : CoroutineScope { // creating local scope
    private var job: Job = Job() // or SupervisorJob() - children of a supervisor job can fail independently of each other
    // To use Dispatchers.Main (CoroutineDispatcher - runs and schedules coroutines) 
    // in Android add dependency: implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-android:1.0.1'
    override val coroutineContext: CoroutineContext
        get() = uiContext + job
    fun detachView() {
        // cancel the job when view is detached
        job.cancel()
    }
    fun login(request: LoginRequest) = launch { // launching a coroutine
        val result = repo.loginUser(request) // calling 'loginUser' function will not block the Main Thread, it suspends the coroutine
        //use result, update UI
        when (result) {
            is Success<LoginResponse> -> { /* update UI when login success */ } 
            is Error -> { /* update UI when login error */ }
        }
    }
}

Answer 2

你可以通过这种方式使用协程

  private var parentJob = Job()
    private val coroutineContext: CoroutineContext
        get() = parentJob + Dispatchers.Main
    private val scope = CoroutineScope(coroutineContext)

 scope.launch(Dispatchers.IO) {
     // your api call 
 }

您可以调用parentJob.cancel()取消作业，也可以在 ViewModel 的清除中调用它