Android - Using RxJava with Retrofit causes an IllegalArgumentException

Question

I tried to use RxJava with Retrofit to chain network requests in Android. But as I stated in the title, it causes an IllegalArgumentException. In the following, you can see my code I have written so far(I also included the imports and the gradle file with the dependencies I use for my project):

ApiClient.java :

import retrofit2.Retrofit;

import retrofit2.adapter.rxjava2.RxJava2CallAdapterFactory;
import retrofit2.converter.gson.GsonConverterFactory;
import retrofit2.http.GET;
import retrofit2.http.Header;
import retrofit2.http.Path;
import rx.Observable;


public class ApiClient {

    // trailing slash is needed
    public static final String BASE_URL = "....";

    private static CliqueDBApiInterface sCliqueDBApiInterface;

    public static CliqueDBApiInterface getCliqueDBApiInterface(){

        if(sCliqueDBApiInterface == null){
            Retrofit retrofit = new Retrofit.Builder()
                    .baseUrl(BASE_URL)
                    .addConverterFactory(GsonConverterFactory.create())
                    .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
                    .build();

            sCliqueDBApiInterface = retrofit.create(CliqueDBApiInterface.class);
        }

        return sCliqueDBApiInterface;
    }

    public interface CliqueDBApiInterface{
        @GET("statementsOfClique/{idOfClique}")
        //Call<ListOfStatements> getStatementsOfTheClique(@Path("idOfClique") int id, @Header("Authorization") String authHeader );
        Observable<ListOfStatements> getStatementsOfTheClique(@Path("idOfClique") int id, @Header("Authorization") String authHeader );
    }

}

MainActivity.java:

import retrofit2.HttpException;
import rx.Observable;
import rx.Subscriber;
import rx.android.schedulers.AndroidSchedulers;
import rx.schedulers.Schedulers;

// ... some other code

Observable<ListOfStatements> call = service.getStatementsOfTheClique(clique.getId(), authenticationToken);

call.subscribeOn(Schedulers.io())
    .observeOn(AndroidSchedulers.mainThread())
    .subscribe(new Subscriber<ListOfStatements>() {
          @Override
          public void onNext(ListOfStatements listOfStatements) {
              // Called once the `ListOfStatements` object is available
              List<Statement> statementList = listOfStatements.getStatementsOfClique();
              // do something with statementList


          }

          @Override
          public void onCompleted() {
             // Nothing to do here
          }

          @Override
          public void onError(Throwable e) {
             if (e instanceof HttpException) {
                int code = ((HttpException) e).code();
             }

          }
});

Now the gradle file:

apply plugin: 'com.android.application'

android {
    compileSdkVersion 28
    defaultConfig {
        applicationId "com.celik.abdullah.hefuxi11"
        minSdkVersion 19
        targetSdkVersion 28
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
    packagingOptions{
        exclude 'META-INF/rxjava.properties'
    }
}

dependencies {
    implementation fileTree(include: ['*.jar'], dir: 'libs')
    implementation 'com.android.support:appcompat-v7:28.0.0'
    implementation 'com.android.support.constraint:constraint-layout:1.1.3'
    implementation 'com.android.support:recyclerview-v7:28.0.0'
    implementation 'com.android.volley:volley:1.1.1'
    implementation 'com.google.code.gson:gson:2.8.5'
    implementation 'com.android.support:cardview-v7:28.0.0'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.2'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
    implementation 'com.squareup.retrofit2:converter-gson:2.5.0'
    implementation 'com.squareup.retrofit2:retrofit:2.5.0'
    implementation 'com.squareup.retrofit2:adapter-rxjava2:2.5.0'
    implementation 'io.reactivex:rxandroid:1.2.0'
    implementation 'io.reactivex:rxjava:1.1.4'
    implementation 'com.squareup.retrofit2:adapter-rxjava2:2.5.0'

}

But the app crashes and I get the following error/exception in the LogCat:

03-13 18:36:29.190 4128-4128/com.celik.abdullah.hefuxi11 E/AndroidRuntime: FATAL EXCEPTION: main Process: com.celik.abdullah.hefuxi11, PID: 4128 java.lang.IllegalArgumentException: Unable to create call adapter for rx.Observable for method CliqueDBApiInterface.getStatementsOfTheClique at retrofit2.Utils.methodError(Utils.java:52) at retrofit2.HttpServiceMethod.createCallAdapter(HttpServiceMethod.java:60) at retrofit2.HttpServiceMethod.parseAnnotations(HttpServiceMethod.java:34) at retrofit2.ServiceMethod.parseAnnotations(ServiceMethod.java:36) at retrofit2.Retrofit.loadServiceMethod(Retrofit.java:168) at retrofit2.Retrofit$1.invoke(Retrofit.java:147) at java.lang.reflect.Proxy.invoke(Proxy.java:913) at $Proxy1.getStatementsOfTheClique(Unknown Source) at com.celik.abdullah.hefuxi11.adapters.CliqueAdapter$1.run(CliqueAdapter.java:124) at android.os.Handler.handleCallback(Handler.java:790) at android.os.Handler.dispatchMessage(Handler.java:99) at android.os.Looper.loop(Looper.java:164) at android.app.ActivityThread.main(ActivityThread.java:6494) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807) Caused by: java.lang.IllegalArgumentException: Could not locate call adapter for rx.Observable. Tried: * retrofit2.adapter.rxjava2.RxJava2CallAdapterFactory * retrofit2.CompletableFutureCallAdapterFactory * retrofit2.ExecutorCallAdapterFactory at retrofit2.Retrofit.nextCallAdapter(Retrofit.java:239) at retrofit2.Retrofit.callAdapter(Retrofit.java:203) at retrofit2.HttpServiceMethod.createCallAdapter(HttpServiceMethod.java:58) ... 14 more

Do somebody know how to resolve that problem? I have found some other SO questions about this exception and tried all answers by playing/changing the import packages in the gradle file but nothing has worked. I also add the addCallAdapterFactory(RxJava2CallAdapterFactory.create()) when I build the retrofit instance but I got the same error.

Thanks in advance,

Answer 1

Yes, either update everything to RxJava2 or you can use RxJava1

in that case your imports would be something like:

/* rx */
implementation 'io.reactivex:rxandroid:1.2.1'
implementation 'io.reactivex:rxjava:1.3.2'

/* retrofit, gson */
implementation 'com.squareup.retrofit2:retrofit:2.4.0'
implementation 'com.squareup.retrofit2:adapter-rxjava:2.3.0'
implementation 'com.squareup.retrofit2:converter-gson:2.4.0'
implementation 'com.squareup.okhttp3:logging-interceptor:3.8.1'
implementation 'com.squareup.retrofit2:converter-scalars:2.4.0'

And then your RetrofitApiInterface would be something like this:

public static CliqueDBApiInterface getCliqueDBApiInterface(){

    if(sCliqueDBApiInterface == null){
        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl(BASE_URL)
                .addCallAdapterFactory(RxJavaCallAdapterFactory.create())
                .addConverterFactory(GsonConverterFactory.create())
                .client(okHttpClient)
                .build();

        sCliqueDBApiInterface = retrofit.create(CliqueDBApiInterface.class);
    }

    return sCliqueDBApiInterface;
}


where okHttpClient = new OkHttpClient.Builder().build();

Answer 2

You are using RxJava 1.x observable and subscribers. You have added adapter factory of RxJava 2.x at .addCallAdapterFactory(RxJava2CallAdapterFactory.create())

you should import from RxJava 2.x

accordingly, you need to update dependency as well

implementation 'io.reactivex.rxjava2:rxandroid:2.1.1'
implementation 'io.reactivex.rxjava2:rxjava:2.2.6'
implementation 'com.squareup.retrofit2:adapter-rxjava2:2.3.0'




import io.reactivex.Observable;
import io.reactivex.schedulers.Schedulers;
import io.reactivex.android.schedulers.AndroidSchedulers;
import io.reactivex.disposables.CompositeDisposable;

Answer 3

To create one call right after another, use flatMap operator instead of creating a Subscriber in your subscribe() method.