Unable to create converter for my class in Android Retrofit library

Im migrating from using Volley to Retrofit, I already have gson class that I used before for converting JSONObject reponse to a object that implements gson annotations. When I'm trying to make http get request using retrofit but then my app crashes with this error :

 Unable to start activity ComponentInfo{com.lightbulb.pawesome/com.example.sample.retrofit.SampleActivity}: java.lang.IllegalArgumentException: Unable to create converter for class com.lightbulb.pawesome.model.Pet
    for method GitHubService.getResponse

Im following the guide in retrofit site and I come up with these implementations :

This is my activity where I am trying to execute the retro http request:

public class SampleActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_sample);

        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl("**sample base url here**")
                .build();

        GitHubService service = retrofit.create(GitHubService.class);
        Call<Pet> callPet = service.getResponse("41", "40");
        callPet.enqueue(new Callback<Pet>() {
            @Override
            public void onResponse(Response<Pet> response) {
                Log.i("Response", response.toString());
            }

            @Override
            public void onFailure(Throwable t) {
                Log.i("Failure", t.toString());
            }
        });
        try{
            callPet.execute();
        } catch (IOException e){
            e.printStackTrace();
        }

    }
}

My interface which turned to be my API

public interface GitHubService {
    @GET("/ **sample here** /{petId}/{otherPet}")
    Call<Pet> getResponse(@Path("petId") String userId, @Path("otherPet") String otherPet);
}

And finally the Pet class which should be the reponse:

public class Pet implements Parcelable {

    public static final String ACTIVE = "1";
    public static final String NOT_ACTIVE = "0";

    @SerializedName("is_active")
    @Expose
    private String isActive;
    @SerializedName("pet_id")
    @Expose
    private String petId;
    @Expose
    private String name;
    @Expose
    private String gender;
    @Expose
    private String age;
    @Expose
    private String breed;
    @SerializedName("profile_picture")
    @Expose
    private String profilePicture;
    @SerializedName("confirmation_status")
    @Expose
    private String confirmationStatus;

    /**
     *
     * @return
     * The confirmationStatus
     */
    public String getConfirmationStatus() {
        return confirmationStatus;
    }

    /**
     *
     * @param confirmationStatus
     * The confirmation_status
     */
    public void setConfirmationStatus(String confirmationStatus) {
        this.confirmationStatus = confirmationStatus;
    }

    /**
     *
     * @return
     * The isActive
     */
    public String getIsActive() {
        return isActive;
    }

    /**
     *
     * @param isActive
     * The is_active
     */
    public void setIsActive(String isActive) {
        this.isActive = isActive;
    }

    /**
     *
     * @return
     * The petId
     */
    public String getPetId() {
        return petId;
    }

    /**
     *
     * @param petId
     * The pet_id
     */
    public void setPetId(String petId) {
        this.petId = petId;
    }

    /**
     *
     * @return
     * The name
     */
    public String getName() {
        return name;
    }

    /**
     *
     * @param name
     * The name
     */
    public void setName(String name) {
        this.name = name;
    }

    /**
     *
     * @return
     * The gender
     */
    public String getGender() {
        return gender;
    }

    /**
     *
     * @param gender
     * The gender
     */
    public void setGender(String gender) {
        this.gender = gender;
    }

    /**
     *
     * @return
     * The age
     */
    public String getAge() {
        return age;
    }

    /**
     *
     * @param age
     * The age
     */
    public void setAge(String age) {
        this.age = age;
    }

    /**
     *
     * @return
     * The breed
     */
    public String getBreed() {
        return breed;
    }

    /**
     *
     * @param breed
     * The breed
     */
    public void setBreed(String breed) {
        this.breed = breed;
    }

    /**
     *
     * @return
     * The profilePicture
     */
    public String getProfilePicture() {
        return profilePicture;
    }

    /**
     *
     * @param profilePicture
     * The profile_picture
     */
    public void setProfilePicture(String profilePicture) {
        this.profilePicture = profilePicture;
    }


    protected Pet(Parcel in) {
        isActive = in.readString();
        petId = in.readString();
        name = in.readString();
        gender = in.readString();
        age = in.readString();
        breed = in.readString();
        profilePicture = in.readString();
    }

    @Override
    public int describeContents() {
        return 0;
    }

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeString(isActive);
        dest.writeString(petId);
        dest.writeString(name);
        dest.writeString(gender);
        dest.writeString(age);
        dest.writeString(breed);
        dest.writeString(profilePicture);
    }

    @SuppressWarnings("unused")
    public static final Parcelable.Creator<Pet> CREATOR = new Parcelable.Creator<Pet>() {
        @Override
        public Pet createFromParcel(Parcel in) {
            return new Pet(in);
        }

        @Override
        public Pet[] newArray(int size) {
            return new Pet[size];
        }
    };
}

If anyone ever comes across this in the future because you are trying to define your own custom converter factory and are getting this error, it can also be caused by having multiple variables in a class with a misspelled or the same serialized name. IE:

public class foo {
  @SerializedName("name")
  String firstName;
  @SerializedName("name")
  String lastName;
}

Having serialized names defined twice (likely by mistake) will also throw this exact same error.

Update: Keep in mind that this logic also holds true via inheritance. If you extend to a parent class with an object that has the same Serialized name as you do in the sub-class, it will cause this same problem.

Prior to 2.0.0, the default converter was a gson converter, but in 2.0.0 and later the default converter is ResponseBody. From the docs:

> By default, Retrofit can only deserialize HTTP bodies into OkHttp's > ResponseBody type and it can only accept its RequestBody type for > @Body.

In 2.0.0+, you need to explicitly specify you want a Gson converter:

Retrofit retrofit = new Retrofit.Builder()
    .baseUrl("**sample base url here**")
    .addConverterFactory(GsonConverterFactory.create())
    .build();

You will also need to add the following dependency to your gradle file:

compile 'com.squareup.retrofit2:converter-gson:2.1.0'

Use the same version for the converter as you do for your retrofit. The above matches this retrofit dependency:

compile ('com.squareup.retrofit2:retrofit:2.1.0')

Also, note as of writing this, the retrofit docs are not completely updated, which is why that example got you into trouble. From the docs:

> Note: This site is still in the process of being expanded for the new 2.0 APIs.

just make sure that you are not using the same serialize name twice

 @SerializedName("name") val name: String
 @SerializedName("name") val firstName: String

just remove one of them

Based on top comment I updated my imports

implementation 'com.squareup.retrofit2:retrofit:2.1.0'
implementation 'com.squareup.retrofit2:converter-gson:2.1.0'

I've used http://www.jsonschema2pojo.org/ in order to create pojo's from Spotify json results and making sure to specify Gson format.

These days there are Android Studio plugins which can create the pojo's or Kotlin data models for you. One great option for mac is Quicktype. https://itunes.apple.com/us/app/paste-json-as-code-quicktype/id1330801220

In my case, I had a TextView object inside my modal class and GSON did not know how to serialize it. Marking it as 'transient' solved the issue.

@Silmarilos's post helped me solve this. In my case, it was that I used "id" as a serialized name, like this:

 @SerializedName("id")
var node_id: String? = null

and I changed it to

 @SerializedName("node_id")
var node_id: String? = null

All working now. I forgot that 'id' is a default attribute.

This may help someone

In my case mistakenly I wrote SerializedName like this

@SerializedName("name","time")
String name,time; 

It should be

@SerializedName("name")
String name;

@SerializedName("time")
String time;

In my case, it was due to trying to take a List being returned by my service into an ArrayList. So what I had was:

@Json(name = "items")
private ArrayList<ItemModel> items;

when I should've had

@Json(name = "items")
private List<ItemModel> items;

Hope this helps someone!

In build.gradle changing

minifyEnabled true

to

minifyEnabled false

has solved my problem.

In my case, the problem was that my SUPERCLASS model had this field defined in it. Very stupid, I know....

Hey i was going through the same issue today took me a whole day to find a solution but this is the solution i found finally. Am using Dagger in my code and i needed to implement the Gson converter in my retrofit instance.

so this was my code before

@Provides
    @Singleton
    Retrofit providesRetrofit(Application application,OkHttpClient client) {
        String SERVER_URL=URL;
        Retrofit.Builder builder = new Retrofit.Builder();
        builder.baseUrl(SERVER_URL);
        return builder
                .client(client)
                .build();
    }

this was what i ended up with

@Provides
    @Singleton
    Retrofit providesRetrofit(Application application,OkHttpClient client, Gson gson) {
        String SERVER_URL=URL;
        Retrofit.Builder builder = new Retrofit.Builder();
        builder.baseUrl(SERVER_URL);
        return builder
                .client(client)
                .addConverterFactory(GsonConverterFactory.create(gson))
                .build();
    }

notice how there is no converter in the first example and the addition if you haven't instantiated Gson you add it like this

    @Provides
    @Singleton
    Gson provideGson() {
        GsonBuilder gsonBuilder = new GsonBuilder();
        
   gsonBuilder.setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES);
        return gsonBuilder.create();
    }

and ensure you have included it in the method call for retrofit.

once again hope this helps some one like me.

In my case I was using the Moshi library with Retrofit 2.0, i.e

// Moshi
implementation 'com.squareup.moshi:moshi-kotlin:1.9.3'
// Retrofit with Moshi Converter
implementation 'com.squareup.retrofit2:converter-moshi:2.9.0'

I forgot to pass in the custom Moshi json converter adapter factory object to the moshi converter factory constructor.

private val moshi = Moshi.Builder() // adapter
    .add(KotlinJsonAdapterFactory())
    .build()

private val retrofit = Retrofit.Builder()
    .addConverterFactory(MoshiConverterFactory.create()) // <- missing moshi json adapter insance
    .baseUrl(BASE_URL)
    .build()

Fix: .addConverterFactory(MoshiConverterFactory.create(moshi))

In my case using kotlinx.serialization, the same exception was raised by retrofit,

it was due to the missing @Serializable annotation.

@Serializable
data class MyClass(
    val id: String
)

in my case, I am using Moshi with Retrofit and my mistake was :

I did not define a body for object that include in Response class service.

for example:

@JsonSerializable
data class Balance(
    @field:Json(name = "balance") var balance: Double,
    @field:Json(name = "currency") var currency: Currency

and the Currency class was emty. so I complete it and the problem fixed!