Android中利用OkHttp+Retrofit+kotlin协程发出网络请求

目前Android端流行的网络请求模式是，OkHttp+retrofit2+RxJava，但是kotlin协程横空出世之后，RxJava的某些特性与kotlin协程出现了冲突，那我们能抛开RxJava吗？ 当然可以，这里，我们示范一种OkHttp+retrofit2+kotlin协程的网络请求模式。

模块的build.gradle添加以下依赖

dependencies {
	implementation 'com.jakewharton.retrofit:retrofit2-kotlin-coroutines-adapter:0.9.2'
}

val retrofit = Retrofit.Builder()
    .client(HttpClient.get(baseApplication.getContext(), httpParams, BuildConfig.DEBUG))
    .baseUrl(baseUrl)
    .addConverterFactory(GsonConverterFactory.create(gson))
    //这里我们改为CoroutineCallAdapterFactory
    .addCallAdapterFactory(CoroutineCallAdapterFactory()) 
    .build()

interface Api {
   @POST("/api/xxx/xxx/xxx")
   fun loginAsync(@Body body: JsonObject): Deferred>
}

与RxJava不同，这里的返回值我们改为Deferred即可

理论上，上面就可以直接用了，但是我们也可以对网络请求的错误做出统一处理，所以封装一个ApiManager类

object ApiManager {
    suspend fun  request(deferred: Deferred>): HttpResponse = withContext(Dispatchers.IO) {
        try {
            return@withContext deferred.await()
        } catch (e: Exception) {
            Log.e("ApiManager", e.message)
            e.printStackTrace()
            val data = createEmpty(e.message.toString())
            val type = object : TypeToken>() {}.type
            return@withContext GsonUtils.gsonToModel(data, type) as HttpResponse
        } catch (e: Throwable) {
            Log.e("ApiManager","throwable")
            val data = createEmpty("请求错误")
            val type = object : TypeToken>() {}.type
            return@withContext GsonUtils.gsonToModel(data, type) as HttpResponse
        }
    }

    private fun createEmpty(msg: String): String {
        val map = androidx.collection.ArrayMap()
        map["code"] = 500
        map["msg"] = msg
        return GsonUtils.toJson(map)
    }
}

    suspend fun login(userName: String, verifyCode: String): HttpResponse {
        //xxx
        body.add("clientInfo", clientInfo)
        return request(bmsApi.loginAsync(body))
    }

如上，我们可以用kotlin协程的做法，就像同步请求一样，非常优雅的做出网络请求。

关键代码就在CoroutineCallAdapterFactory类中，我们可以研究下这个类，这里也示范下如何将callback改装为kotlin协程。

  private class ResponseCallAdapter(
      private val responseType: Type
  ) : CallAdapter>> {

    override fun responseType() = responseType

    override fun adapt(call: Call): Deferred> {
      val deferred = CompletableDeferred>()

      deferred.invokeOnCompletion {
        if (deferred.isCancelled) {
          call.cancel()
        }
      }
	  //进行网络请求
      call.enqueue(object : Callback {
        override fun onFailure(call: Call, t: Throwable) {
          deferred.completeExceptionally(t)
        }

        override fun onResponse(call: Call, response: Response) {
          //返回网络请求结果
          deferred.complete(response)
        }
      })

      return deferred
    }
  }
}