How can I return String or JSONObject from asynchronous callback using Retrofit?

Question

For example, calling

api.getUserName(userId, new Callback() {...});

cause:

retrofit.RetrofitError: retrofit.         


        

Answer 1

Retrofit 2.0.0-beta3 adds a converter-scalars module provides a Converter.Factory for converting String, the 8 primitive types, and the 8 boxed primitive types as text/plain bodies. Install this before your normal converter to avoid passing these simple scalars through, for example, a JSON converter.

So, first add converter-scalars module to build.gradle file for your application.

dependencies {
    ...
    // use your Retrofit version (requires at minimum 2.0.0-beta3) instead of 2.0.0
    // also do not forget to add other Retrofit module you needed
    compile 'com.squareup.retrofit2:converter-scalars:2.0.0'
}

Then, create your Retrofit instance like this:

new Retrofit.Builder()
        .baseUrl(BASE_URL)
        // add the converter-scalars for coverting String
        .addConverterFactory(ScalarsConverterFactory.create())
        .addConverterFactory(GsonConverterFactory.create())
        .addCallAdapterFactory(RxJavaCallAdapterFactory.create())
        .build()
        .create(Service.class);

Now you can use API declaration like this:

interface Service {

    @GET("/users/{id}/name")
    Call userName(@Path("userId") String userId);

    // RxJava version
    @GET("/users/{id}/name")
    Observable userName(@Path("userId") String userId);
}