UseCase.java

package com.example.features;

import android.os.AsyncTask;
import android.support.annotation.VisibleForTesting;

/**
 * @param <ARG> the type of arguments that can be passed in when executing this use case.
 * @param <RESULT> the type of the outcome generated by this use case and passed its callback.
 */
public abstract class UseCase<ARG, RESULT> {
    /*
    If we generify the calling code within this base class, it will force subclasses to
    explicitly define types for each generic type.  In this case, that's really unnecessary
    and adds a bunch of boilerplate to each and every sub-type.
    We've opted to, instead, ignore warnings about unchecked invocations.
    So as to not get carried away, we comment each "offending" statement, not this whole class.
     */

    /**
     * The implementation of this use case.
     *
     * @param args the same arguments passed into {@link #execute(Callback, Object[])}
     * @return the return value that should be passed to callbacks of this UseCase.
     */
    public abstract RESULT run(final ARG... args);

    public interface Callback<RESULT> {
        void execute(RESULT result);
    }

    public UseCaseTask execute(final Callback callback, final ARG... args) {
        //noinspection unchecked
        return newUseCaseTask().execute(callback, args);
    }

    protected UseCaseTask newUseCaseTask() {
        return new AsyncUseCaseTask();
    }

    private class AsyncUseCaseTask implements UseCaseTask<ARG> {
        private AsyncTask<ARG, Void, RESULT> mAsyncTask;
        private Callback mCallback;

        @SafeVarargs
        @Override
        public final UseCaseTask execute(final Callback callback, final ARG... args) {
            mCallback = callback;
            mAsyncTask = new AsyncTask<ARG, Void, RESULT>() {
                @SafeVarargs
                @Override
                protected final RESULT doInBackground(final ARG... args1) {
                    return UseCase.this.run(args1);
                }

                @Override
                public void onPostExecute(final RESULT result) {
                    // noinspection unchecked
                    mCallback.execute(result);
                }
            };
            mAsyncTask = mAsyncTask.execute(args);
            return this;
        }

        @Override
        public boolean cancel(final boolean mayInterruptIfRunning) {
            return mAsyncTask.cancel(mayInterruptIfRunning);
        }
    }
}