MainActivity.java

/*
 * Copyright (C) 2012 The Android Open Source Project
 *
 * 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.fragments;

import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentTransaction;

public class MainActivity extends FragmentActivity implements HeadlinesFragment.OnHeadlineSelectedListener {

  int mCurrentArticle = -1;

  /**
   * Called when the activity is first created.
   */
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.news_articles);

    // Check whether the activity is using the layout version with
    // the fragment_container FrameLayout. If so, we must add the first fragment
    if (findViewById(R.id.fragment_container) != null) {

      // However, if we're being restored from a previous state,
      // then we don't need to do anything and should return or else
      // we could end up with overlapping fragments.
      if (savedInstanceState != null) {
        return;
      }

      // Create an instance of ExampleFragment
      HeadlinesFragment firstFragment = new HeadlinesFragment();

      // In case this activity was started with special instructions from an Intent,
      // pass the Intent's extras to the fragment as arguments
      firstFragment.setArguments(getIntent().getExtras());

      // Add the fragment to the 'fragment_container' FrameLayout
      getSupportFragmentManager().beginTransaction()
          .add(R.id.fragment_container, firstFragment).commit();
    }
  }

  public void onArticleSelected(int position) {
    mCurrentArticle = position;
    // The user selected the headline of an article from the HeadlinesFragment

    // Capture the article fragment from the activity layout
    ArticleFragment articleFrag = (ArticleFragment)
        getSupportFragmentManager().findFragmentById(R.id.article_fragment);

    if (articleFrag != null) {
      // If article frag is available, we're in two-pane layout...

      // Call a method in the ArticleFragment to update its content
      articleFrag.updateArticleView(position);

    } else {
      // If the frag is not available, we're in the one-pane layout and must swap frags...

      // Create fragment and give it an argument for the selected article
      ArticleFragment newFragment = new ArticleFragment();
      Bundle args = new Bundle();
      args.putInt(ArticleFragment.ARG_POSITION, position);
      newFragment.setArguments(args);
      FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();

      /**
       * set the sliding animation
       *
       * first param is for the next fragment's anim
       * second param is for the current fragment's anim
       * third param is for the back stack fragment's anim
       * fourth is for the fragment's anim that user presses back button on
       */
      transaction.setCustomAnimations(R.anim.slide_in_from_right,
          R.anim.slide_out_to_left,
          R.anim.slide_in_from_left,
          R.anim.slide_out_to_right);

      // Replace whatever is in the fragment_container view with this fragment,
      // and add the transaction to the back stack so the user can navigate back
      transaction.replace(R.id.fragment_container, newFragment);

      transaction.addToBackStack(null);

      // Commit the transaction
      transaction.commit();
    }
  }

  /**
   * Override the onBackPressed so that we can change the activity title (title on action bar)
   */
  @Override
  public void onBackPressed() {
    super.onBackPressed();
    if (mCurrentArticle != -1) {
      setTitle("Main Activity Title: " + mCurrentArticle);
    }
  }

}