原文地址：https://proandroiddev.com/forget-rxjava-kotlin-coroutines-are-all-you-need-part-1-2-4f62ecc4f99b
使用RxJava創(chuàng)建GithubApi的網(wǎng)絡(luò)層的接口如下：

interface ApiClientRx {

    fun login(auth: Authorization) : Single<GithubUser>
    fun getRepositories(reposUrl: String, auth: Authorization) : Single<List<GithubRepository>>
    fun searchRepositories(query: String) : Single<List<GithubRepository>>
  
}

雖然Rxjava是一個功能強大的庫，但它不能用作管理異步任務(wù)的工具讶踪，他是一個事件處理庫。
接口使用方法如下所示：

private fun attemptLoginRx(){
  val login = email.text.toString()
  val pass = password.test.toString()
  
  val auth = BasicAuthorization(login, pass)
  val apiClient = ApiClientRx.ApiClientRxImpl()
  showProgressVisible(true)
  compositeDisposable.add(apiClient.login(auth)
    .flatMap {
        user -> apiClient.getRepositories(user.reposUrl, auth)
    }
    .map { list -> list.map { it.fullName } }
    .subscribeOn(Schedulers.io())
    .observeOn(AndroidSchedulers.mainThread())
    .doAfterTerminate { showProgressVisible(false) }
    .subscribe(
            { list -> showRepositories(this@LoginActivity, list) },
            { error -> Log.e("TAG", "Failed to show repos", error) }
    ))
}

這段代碼有幾個隱含的缺陷：

性能開銷

這里的每一行都生成一個內(nèi)部對象來完成這項工作泛鸟，對于這種特殊情況，他生成了19個對象，如果更復(fù)雜的例子裕膀，那么將會生成更多的對象：

image.png

不可讀的堆棧跟蹤

如果你的代碼中發(fā)生了一個錯誤，那么如下的堆棧跟蹤相當(dāng)不好理解：

at com.epam.talks.github.model.ApiClientRx$ApiClientRxImpl$login$1.call(ApiClientRx.kt:16)
at io.reactivex.internal.operators.single.SingleFromCallable.subscribeActual(SingleFromCallable.java:44)
at io.reactivex.Single.subscribe(Single.java:3096)
at io.reactivex.internal.operators.single.SingleFlatMap.subscribeActual(SingleFlatMap.java:36)
at io.reactivex.Single.subscribe(Single.java:3096)
at io.reactivex.internal.operators.single.SingleMap.subscribeActual(SingleMap.java:34)
at io.reactivex.Single.subscribe(Single.java:3096)
at io.reactivex.internal.operators.single.SingleSubscribeOn$SubscribeOnObserver.run(SingleSubscribeOn.java:89)
at io.reactivex.Scheduler$DisposeTask.run(Scheduler.java:463)
at io.reactivex.internal.schedulers.ScheduledRunnable.run(ScheduledRunnable.java:66)
at io.reactivex.internal.schedulers.ScheduledRunnable.call(ScheduledRunnable.java:57)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:301)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1162)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:636)
at java.lang.Thread.run(Thread.java:764)

整個堆棧跟蹤中只有一行來自你的代碼勇哗。

學(xué)習(xí)的復(fù)雜性

還記得你花了多少時間用來理解map()和flatmap()的不同之處嗎昼扛。更不用說還有其他更多的操作符，這些時間是每個新的開發(fā)人員進(jìn)入響應(yīng)式變成世界都需要花費的欲诺。

Kotlin Coroutines能否讓我們的生活更好抄谐？

public actual interface Deferrd<out T>: Job {
  public suspend fun await() : T
}

interface Job：CoroutineContext.Element {
  public val isActive: Boolean
  public val isCompleted: Boolean
  public val isCancelled: Boolean
  public fun getCancellationException: CancellationException
  public fun start(): Boolean
}

接下來重構(gòu)代碼：

interface ApiClient {
  fun login(auth: Authorization) : Deferred<GithubUser>
  fun getRepositories(reposUrl: String, auth: Authorization): Deffered<List<GithubRepository>>
}

override fun login(auth: Authorization) : Deferred<GithubUser?> = async {
    val response = get("https://api.github.com/user", auth = auth)
    if (response.statusCode != 200) {
        throw RuntimeException("Incorrect login or password")
    }

    val jsonObject = response.jsonObject
    with (jsonObject) {
        return@async GithubUser(getString("login"), getInt("id"),
                getString("repos_url"), getString("name"))
    }
}

acync和launch構(gòu)建器使用CommonPool調(diào)度程序渺鹦。

job = launch(UI){
  showProgressVisible(true);
  val auth = BasicAuthorization(login,pass)
  try{
    val userInfo = login(auth).await()
    val repoUrl = userInfo.reposUrl
    val repos = getRepositories(repoUrl, auth).await()
    val pullRequests = getPullRequests(repos[0], auth).await()
    showRepositories(this, repos.map { it -> it.fullName })
  } catch (e: RuntimeException) {
    Toast.makeText(this, e.message, LENGTH_LONG).show()
  } finally {
    showProgressVisible(false)
  }
}

代碼變得更加的清晰和直觀，看起來就像沒有任何異步發(fā)生蛹含，在RxJava中我們還需要將subscription添加到compositeDisposable中毅厚，以便將它放在onStop中。

性能

對象數(shù)量下降到了11

image.png

不可讀的堆棧

堆棧信息依舊不可讀但是這個問題正在被解決.

可讀性

代碼更易于讀寫浦箱，因為是用同步的方法編寫的吸耿。

如何重構(gòu)測試代碼？

使用RxJava的測試代碼是如下的樣子：

@Test
    fun login() {
        val apiClientImpl = ApiClientRx.ApiClientRxImpl()
        val genericResponse = mockLoginResponse()

        staticMockk("khttp.KHttp").use {
            every { get("https://api.github.com/user", auth = any()) } returns genericResponse

            val githubUser = apiClientImpl.login(BasicAuthorization("login", "pass"))

            githubUser.subscribe { githubUser ->
                Assert.assertNotNull(githubUser)
                Assert.assertEquals("name", githubUser.name)
                Assert.assertEquals("url", githubUser.reposUrl)
            }

        }
    }

使用kotin Coroutine 之后的測試代碼如下：

@Test
    fun login() {
        val apiClientImpl = ApiClient.ApiClientImpl()
        val genericResponse = mockLoginResponse()

        staticMockk("khttp.KHttp").use {
            every { get("https://api.github.com/user", auth = any()) } returns genericResponse

            runBlocking {
                val githubUser = apiClientImpl.login(BasicAuthorization("login", "pass")).await()

                assertNotNull(githubUser)
                assertEquals("name", githubUser.name)
                assertEquals("url", githubUser.repos_url)
            }
        }
    }

還有更進(jìn)一步的改進(jìn)嗎憎茂？

我們使用suspend修飾符替換Deferred對象

interface SuspendingApiClient {

    suspend fun login(auth: Authorization) : GithubUser
    suspend fun getRepositories(reposUrl: String, auth: Authorization) : List<GithubRepository>
    suspend fun searchRepositories(searchQuery: String) : List<GithubRepository>

}

接下來看一下客戶端代碼和測試代碼的改變:

private fun attemptLoginSuspending() {
        val login = email.text.toString()
        val pass = password.text.toString()
        val apiClient = SuspendingApiClient.SuspendingApiClientImpl()
        job = launch(UI) {
            showProgressVisible(true)
            val auth = BasicAuthorization(login, pass)
            try {
                val userInfo = async(parent = job) { apiClient.login(auth) }.await()
                val repoUrl = userInfo.repos_url
                val list = async(parent = job) { apiClient.getRepositories(reposUrl, auth) }.await()
                showRepositories(this, list.map { it -> it.fullName })
            } catch (e: RuntimeException) {
                Toast.makeText(this, e.message, LENGTH_LONG).show()
            } finally {
                showProgressVisible(false)
            }
        }
    }

跟之前的對比只加了async(parent=job){}

為了在onStop中取消job時取消此協(xié)同程序，需要傳遞父對象锤岸。

@Test
fun testLogin() = runBlocking {
    val apiClient = mockk<SuspendingApiClient.SuspendingApiClientImpl>()
    val githubUser = GithubUser("login", 1, "url", "name")
    val repositories = GithubRepository(1, "repos_name", "full_repos_name")

    coEvery { apiClient.login(any()) } returns githubUser
    coEvery { apiClient.getRepositories(any(), any()) } returns repositories.asList()

    val loginPresenterImpl = SuspendingLoginPresenterImpl(apiClient, CommonPool)
      runBlocking {
        val repos = loginPresenterImpl.doLogin("login", "password")
            assertNotNull(repos)
        }
    }