Android Retrofit 2 custom callback

Shubham Agarwal

8 May 2017

Retrofit 2 is one the best library I have used it so far. There are many cases in which we can use custom callback for our response callback such as Error Handling, Response Handling, Custom Response and much more.

By using a custom callback or any piece of custom code in an application we are promoting object oriented design pattern and thus reducing your efforts that are needed/mandatory to follow if not using it.

Here is an example of Custom Callback that is used to handle error , hide dialog and return response data to original callback.

How it is helpful?

By using Custom Callback, we are preventing from extra effort required to handle error in each request. Plus, we can perform custom operation that are required whenver the response is recieved. In this case we are just hidding the AlertDialog.

public class RetrofitCallback<T> implements Callback<T> {
    @SuppressWarnings("unused")
    private static final String TAG = "RetrofitCallback";
    private Context mContext;
    private final Callback<T> mCallback;

    public RetrofitCallback(Context context, Callback<T> callback) {
        mContext = context;
        this.mCallback = callback;
    }

    @Override
    public void onResponse(Call<T> call, Response<T> response) {
// Do application relavent custom operation like manupulating reponse etc.
        AlertDialogHelper.dismiss(mContext);
        mCallback.onResponse(call, response);
    }

    @Override
    public void onFailure(Call<T> call, Throwable t) {
// Handle error etc.
        NetworkHelper.onFailure(t, (Activity) mContext);
        mCallback.onFailure(call, t);
    }
}

public class RetrofitCallback<T> implements Callback<T> {

@SuppressWarnings("unused")

private static final String TAG = "RetrofitCallback";

private Context mContext;

private final Callback<T> mCallback;

public RetrofitCallback(Context context, Callback<T> callback) {

mContext = context;

this.mCallback = callback;

}

@Override

public void onResponse(Call<T> call, Response<T> response) {

// Do application relavent custom operation like manupulating reponse etc.

AlertDialogHelper.dismiss(mContext);

mCallback.onResponse(call, response);

}

@Override

public void onFailure(Call<T> call, Throwable t) {

// Handle error etc.

NetworkHelper.onFailure(t, (Activity) mContext);

mCallback.onFailure(call, t);

}

We can use this callback instead of our existing callback. e.g.

     RetrofitClient.getClient().create(ApiInterface.class).getHomePageData().enqueue(new RetrofitCallback<>(SplashScreenActivity.this, mHomePageResponseCallback));

1	RetrofitClient.getClient().create(ApiInterface.class).getHomePageData().enqueue(new RetrofitCallback<>(SplashScreenActivity.this, mHomePageResponseCallback));

And Here is the original callback which gets called from our Custom RetrofitCallback

  private Callback<HomePageResponse> mHomePageResponseCallback = new Callback<HomePageResponse>() {
        @Override
        public void onResponse(Call<HomePageResponse> call, Response<HomePageResponse> response) {
            // Handle response data
        }

        @Override
        public void onFailure(Call<HomePageResponse> call, Throwable t) {
// i don't think that would be required right now as the Error is already handled in Custom Callback
        }
    };

private Callback<HomePageResponse> mHomePageResponseCallback = new Callback<HomePageResponse>() {

@Override

public void onResponse(Call<HomePageResponse> call, Response<HomePageResponse> response) {

// Handle response data

}

@Override

public void onFailure(Call<HomePageResponse> call, Throwable t) {

// i don't think that would be required right now as the Error is already handled in Custom Callback

}

};

That’s all it take for laziness!