Retrofit 2.6.0 exception: java.lang.IllegalArgumentException: Unable to create call adapter for kotlinx.coroutines.Deferred

Question

I have a project with Kotlin coroutines and Retrofit.

I had these dependencies:

implementation 'com.squareup.retrofit2:retrofit:2.5.0' implementation 'com.squareup.retrofit2:converter-gson:2.5.0' implementation 'com.jakewharton.retrofit:retrofit2-kotlin-coroutines-adapter:0.9.2' 

Today I have updated Retrofit to 2.6.0 in the project. In https://github.com/JakeWharton/retrofit2-kotlin-coroutines-adapter it is written that it is deprecated now. In https://github.com/square/retrofit/blob/master/CHANGELOG.md#version-260-2019-06-05 it is written that Retrofit currently supports suspend.

So, I removed retrofit2-kotlin-coroutines-adapter:0.9.2 and in Retrofit client changed these lines:

        retrofit = Retrofit.Builder()             .baseUrl(SERVER_URL)             .client(okHttpClient)             .addConverterFactory(MyGsonFactory.create(gson))             //.addCallAdapterFactory(CoroutineCallAdapterFactory()) - removed it.             .build() 

When run, the first request catches an exception:

java.lang.IllegalArgumentException: Unable to create call adapter for kotlinx.coroutines.Deferred<com.package.model.response.UserInfoResponse>     for method Api.getUserInfo 

As I understood, instead of CoroutineCallAdapterFactory() I could use CallAdapter.Factory(), but it is abstract.

If in Api class I change a request adding suspend in the beginning:

@FormUrlEncoded @POST("user/info/") suspend fun getUserInfo(@Field("token") token: String): Deferred<UserInfoResponse>  override suspend fun getUserInfo(token: String): Deferred<UserInfoResponse> =     service.getUserInfo(token) 

I get this exception:

java.lang.RuntimeException: Unable to invoke no-args constructor for kotlinx.coroutines.Deferred<com.package.model.response.UserInfoResponse>. Registering an InstanceCreator with Gson for this type may fix this problem. 

Answer 1

Reading https://github.com/square/retrofit/blob/master/CHANGELOG.md#version-260-2019-06-05 I saw:

New: Support suspend modifier on functions for Kotlin! This allows you to express the asynchrony of HTTP requests in an idiomatic fashion for the language.

@GET("users/{id}") suspend fun user(@Path("id") long id): User

Behind the scenes this behaves as if defined as fun user(...): Call and then invoked with Call.enqueue. You can also return Response for access to the response metadata.

Currently this integration only supports non-null response body types. Follow issue 3075 for nullable type support.

I changed requests so: added suspend and removed Deferred:

@FormUrlEncoded @POST("user/info/") suspend fun getUserInfo(@Field("token") token: String): UserInfoResponse   override suspend fun getUserInfo(token: String): UserInfoResponse =     service.getUserInfo(token) 

Then in interactor (or simply when called the method getUserInfo(token)) removed await():

override suspend fun getUserInfo(token: String): UserInfoResponse =     // api.getUserInfo(token).await() - was before.     api.getUserInfo(token) 

UPDATE

Once I encountered a situation when downloading PDF files required removing suspend in Api class. See How to download PDF file with Retrofit and Kotlin coroutines?.