通过协程创建两个序列 http 请求。 第二个请求必须在第一个完成时等待

Question

Android studio 3.5 In my project I use retrofit and kotlin. I want to the next steps by Kotlin coroutine:

1. Start first http request by retrofit.
2. Only after success finish then start second http request by retrofit.
3. If first request fail then NOT start second request.

Is it possible to do this by Kotlin coroutines?

Thanks.

Answer 1

Yes, it's totally doable with coroutines:

interface MyApi{
    @GET
    suspend fun firstRequest(): Response<FirstRequestResonseObject>
    @GET
    suspend fun secondRequest(): Response<SecondRequestResponseObject>
}

Now, the call:

coroutineScope.launch{
  //Start first http request by retrofit.
  val firstRequest = api.getFirstRequest()
  if(firstRequest.isSuccessFul){
    //Only after success finish then start second http request by retrofit.
    val secondRequest = api.getSecondRequest()
  }
 //If first request fail then NOT start second request.
}

But, you might wanna consider your exceptions:

val coroutineExceptionHandler = CoroutineExceptionHandler{_, throwable -> throwable.printStackTrace()
}

And then:

coroutineScope.launch(coroutineExceptionHandler ){
      val firstRequest = api.getFirstRequest()
      if(firstRequest.isSuccessFul){
        val secondRequest = api.getSecondRequest()
      }
    }

Done!

For this approach, you must have retrofit 2.6 or above. Otherwise your responses should be Deferred<Response<FirstResponseObject>> and the requests api.getFirstRequest().await()