CODEWITHSUNDEEP
androidkotlinretrofitrx-java2
ivan
ivan

Reputation: 65

Retrofit Single<T> blocking UI thread

Retrofit first request with Single blocks UI thread. Below is relevant code, and more text:

RetrofitProvider

object RetrofitProvider {

private val TAG: String = RetrofitProvider::class.java.simpleName

val retrofit: Retrofit by lazy {
    val httpClient = OkHttpClient.Builder()
        .addInterceptor {
            val request = it.request()
            if (BuildConfig.DEBUG) {
                Log.d(TAG, "${request.method()}: ${request.url()}")
            }

            it.proceed(request)
        }
        .build()

    Retrofit.Builder()
        .client(httpClient)
        .baseUrl("http://192.168.0.10:3000")
        .addCallAdapterFactory(RxJava2CallAdapterFactory.createWithScheduler(Schedulers.io()))
        .addConverterFactory(JacksonConverterFactory.create(jacksonObjectMapper()))
        .build()
}
}

ProductApi

interface ProductApi {

@GET("/products")
fun getProducts(): Single<List<Product>>

}

MainViewModel

    fun fetchProducts() {
    productData.value = Resource.Loading()
    productApi.getProducts() // <- This call is a problem (even when I comment out all code below)
        .subscribeOn(Schedulers.io())
        .subscribe(
            {
                productData.postValue(Resource.Success(it))
            },
            {
                productData.postValue(Resource.Fail(it.message))
            })
        .addTo(disposableContainer)
}

MainFragment

...
        button.setOnClickListener {
        Toast.makeText(requireContext(), "click", Toast.LENGTH_SHORT).show()
        mainViewModel.fetchProducts()
    }
...

App flow is simple, clicking a button on MainFragment calls MainViewModel's fetchProducts() which uses retrofit to fetch some stuff.

productApi.getProducts() happens on UI thread and blocks it significantly(~half a second), even Toast is delayed, even though it should be shown immediately on button click, before getProducts() call.

productApi.getProducts() by itself, without subscribe doesn't send network request (I checked on server side), it just prepares Single.

Important note, delay DOES NOT happen on subsequent clicks to button. Just the first time, I guess creating Single<> is expensive operation.

So my question is, why is UI thread blocked on first request, and how do I fix it the way it isn't ugly/hacking.

Also Observable acts the same, but Completable works much faster, but I need the data, so can't use Completable.

Upvotes: 0

Views: 1500

Answers (3)

Gil G
Gil G

Reputation: 1869

When you invoke a RxJava action, for example, a retrofit request you can to tell it where to perform the action and where to get the result the default location is where you subscribe to it in order to change it you need to add two lines

observeOn(Where you will receive the result)
subscribeOn(Where the action will be executed)

In your case, it should be something like this

productApi.getProducts() // <- This call is a problem (even when I comment out all code below)
  .observeOn(AndroidSchedulers.mainThread())
  .subscribeOn(Schedulers.io()) //or .subscribeOn(Schedulers.newThread())
  .subscribe({Success},{Failure})

I have made a library that has a lot of utilities/extensions for Android development in kotlin.

One of the packages is there to make it simple to avoid this issue.

All you need to do is type:

yourObservable //or any other reactive type
   .runSafeOnMain() //it will perform you action in another thread and it will return the result in main
   .subscribe({}, {])

Upvotes: 0

luxa
luxa

Reputation: 36

Returning Completable also blocks the UI thread but for less time than returning Single or Observable so it seems like it doesn't have any impact but it does.

Invoking the API call on a background thread will not block your UI as the converter creation will not happen on the UI thread.

Something like this does the trick.

    Completable.complete()
        .observeOn(Schedulers.io())
        .subscribe {
            productApi.getProducts()
                .subscribe(
                    {
                        productData.postValue(Resource.Success(it))
                    },
                    {
                        productData.postValue(Resource.Fail(it.message))
                    }
                )
                .addTo(disposableContainer)
        }
        .addTo(disposableContainer)

Another thing you can do instead of using the converter is to make a wrapper class around the Retrofit API which will call it in a fitting observable on a background thread.

    fun getProducts() = Single.create<List<Product>> { emitter ->
        try {
            val response = productApi.getProducts().execute()
            if (!response.isSuccessful) {
                throw HttpException(response)
            }

            emitter.onSuccess(response.body()!!)
        } catch (e: Exception) {
            emitter.onError(e)
        }
    }.observeOn(Schedulers.io())

Upvotes: 0

Danail Alexiev
Danail Alexiev

Reputation: 7772

I think your problem lies with the lazy initialisation of your Retrofit object. It will be deferred to the last possible moment, so I guess the first time you click on the button, you create the expensive retrofit button (this is done on the main thread).

My suggestion is to remove the lazy initialisation and try running the app once again.

Upvotes: 1

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