Lova – Java 8 functional interface for AsyncTask on Android

I call the class Lova – in Swedish “to promise something” is “att lova något” .

This assumes you have converted your Android project to compile with Jack.

Warning: Lambdas do not currently work with multidex! See issue 226867.

This implementation only supports a single input parameter to the background task, but it the doInBackground method could easily be changed to send the full array instead.

If you need to report progress or handle cancellation of the AsyncTask, this implementation is too simple.

AsyncTaskResult.java:

package com.claimtowers.common.asynctask;

public class AsyncTaskResult<T> {
    private T result;
    private Exception exception;

    public AsyncTaskResult(T result) {
        this.result = result;
    }

    public AsyncTaskResult(Exception exception) {
        this.exception = exception;
    }

    public T getResult() {
        return result;
    }

    public Exception getException() {
        return exception;
    }
}

Example.java:

new Lova<Integer, TowerMetadata>(id -> towersHttpClient.retrieveTowerMetadata(id))
  .onSuccess(this::showTowerMetadata)
  .onError(this::displayError)
  .execute(towerId);

Lova.java:

package com.claimtowers.common.asynctask;

import android.os.AsyncTask;

import java.util.function.Consumer;
import java.util.function.Function;

public class Lova<Param, Result> extends AsyncTask<Param, Void, AsyncTaskResult<Result>> {

    private final Function<Param, Result> function;
    private Consumer<Result> consumer;
    private Consumer<Exception> errorHandler;

    public Lova(Function<Param, Result> function) {
        this.function = function;
    }

    public Lova<Param, Result> onSuccess(Consumer<Result> consumer) {
        this.consumer = consumer;
        return this;
    }

    public Lova<Param, Result> onError(Consumer<Exception> errorHandler) {
        this.errorHandler = errorHandler;
        return this;
    }

    @Override
    protected AsyncTaskResult<Result> doInBackground(Param... params) {
        try {
            return new AsyncTaskResult<>(function.apply(params[0]));
        } catch (Exception e) {
            cancel(false);
            return new AsyncTaskResult<>(e);
        }
    }

    @Override
    protected void onPostExecute(AsyncTaskResult<Result> asyncTaskResult) {
        super.onPostExecute(asyncTaskResult);
        consumer.accept(asyncTaskResult.getResult());
    }

    @Override
    protected void onCancelled(AsyncTaskResult<Result> asyncTaskResult) {
        super.onCancelled(asyncTaskResult);
        errorHandler.accept(asyncTaskResult.getException());
    }
}

Source: gist cc4f008cf9e90911d3e1d2dbcce2b7f1