MainFragment.java

/*
 * Copyright 2016 Google Inc. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.example.android.agera.basicsamplewithoutcallbacks;

import static java.util.concurrent.Executors.newSingleThreadExecutor;

import com.google.android.agera.Observable;
import com.google.android.agera.Repositories;
import com.google.android.agera.Repository;
import com.google.android.agera.Result;
import com.google.android.agera.Updatable;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.content.ContextCompat;
import android.support.v4.widget.SwipeRefreshLayout;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.Toast;

import java.util.List;
import java.util.concurrent.ExecutorService;

/**
 * The MainFragment contains a {@link ListView} that displays a list of usernames. The usernames
 * are loaded in {@link Fragment#onResume()} and there is a {@link SwipeRefreshLayout} allowing the
 * user to manually refresh the list of usernames.
 * <P >
 * This is set up as an {@link Updatable} as changes in the {@link #usernamesRepository} should
 * trigger the MainFragment to redraw itself.
 */
public class MainFragment extends Fragment implements Updatable {

  /**
   * The {@link SwipeRefreshLayout.OnRefreshListener} is also an {@link Observable}. It is
   * observed by the {@link #usernamesRepository}, an update is triggered whenever
   * {@link SwipeRefreshLayout.OnRefreshListener#onRefresh()} is fired.
   */
  private OnRefreshObservable refreshObservable;

  /**
   * The usernames repository takes care of providing the data to this fragment. It is created
   * using Agera's repository compiler.
   *
   * @see #setUpRepository()
   */
  private Repository<Result<List<String>>> usernamesRepository;

  private ListAdapter listAdapter;

  private ListView listView;

  private SwipeRefreshLayout swipeRefreshLayout;

  private ExecutorService networkExecutor;

  @Override
  public View onCreateView(LayoutInflater inflater, ViewGroup container,
      Bundle savedInstanceState) {
    View root = inflater.inflate(R.layout.main_frag, container, false);

    listView = (ListView) root.findViewById(R.id.list);

    // Set pull to refresh as an observable and attach it to the view
    refreshObservable = new OnRefreshObservable();
    swipeRefreshLayout = (SwipeRefreshLayout) root.findViewById(R.id.refresh_layout);
    swipeRefreshLayout.setColorSchemeColors(
        ContextCompat.getColor(getActivity(), R.color.colorPrimary),
        ContextCompat.getColor(getActivity(), R.color.colorAccent),
        ContextCompat.getColor(getActivity(), R.color.colorPrimaryDark));
    swipeRefreshLayout.setOnRefreshListener(refreshObservable);

    setUpRepository();

    return root;
  }

  private void setUpRepository() {
    // Set up background executor
    networkExecutor = newSingleThreadExecutor();

    // Set up usernames repository
    usernamesRepository = Repositories
        .repositoryWithInitialValue(Result.<List<String>>absent())
        .observe(refreshObservable)
        .onUpdatesPerLoop()
        .goTo(networkExecutor)
        .thenGetFrom(new UsernamesSupplier())
        .compile();
  }

  @Override
  public void onResume() {
    super.onResume();

    // We make sure the main fragment observes the repository. This will also trigger the
    // repository to update itself.
    usernamesRepository.addUpdatable(this);

    // We update the UI to show the data is being updated. We need to wait for the
    // SwipeRefreshLayout to be ready before asking it to show itself as refreshing.
    swipeRefreshLayout.post(new Runnable() {
      @Override
      public void run() {
        update();
      }
    });
  }

  @Override
  public void onPause() {
    super.onPause();

    // We remove the observations to avoid triggering updates when they aren't needed
    usernamesRepository.removeUpdatable(this);
  }

  /**
   * As this MainFragment is observing the {@link #usernamesRepository}, this is triggered
   * whenever the {@link #usernamesRepository} updates itself.
   */
  @Override
  public void update() {
     // Result has methods to differentiate between success and failure.
     // Process Result.isAbsent() first because Result.failed() is true if Result.isAbsent() is
     // true.
    if (usernamesRepository.get().isAbsent()) {
      swipeRefreshLayout.setRefreshing(true);
    } else if (usernamesRepository.get().failed()) {
      // Show error message, do not update list as we still want to show the last known list
      // of usernames
      Toast.makeText(getContext(), getResources().getString(R.string.error),
          Toast.LENGTH_LONG).show();
      swipeRefreshLayout.setRefreshing(false);
    } else { // Success
      // Update the list of usernames
      listAdapter = new ArrayAdapter<String>(getContext(),
          android.R.layout.simple_list_item_1, usernamesRepository.get().get());
      listView.setAdapter(listAdapter);
      swipeRefreshLayout.setRefreshing(false);
    }
  }
}