android/newsreader/NewsReaderActivity.java

/*
 * Copyright (C) 2011 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.newsreader;

import android.app.AlertDialog;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.Build;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.SpinnerAdapter;

/**
 * Main activity: shows headlines list and articles, if layout permits.
 *
 * This is the main activity of the application. It can have several different layouts depending
 * on the SDK version, screen size and orientation. The configurations are divided in two large
 * groups: single-pane layouts and dual-pane layouts.
 *
 * In single-pane mode, this activity shows a list of headlines using a {@link HeadlinesFragment}.
 * When the user clicks on a headline, a separate activity (a {@link ArticleActivity}) is launched
 * to show the news article.
 *
 * In dual-pane mode, this activity shows a {@HeadlinesFragment} on the left side and an
 * {@ArticleFragment} on the right side. When the user selects a headline on the left, the
 * corresponding article is shown on the right.
 *
 * If an Action Bar is available (large enough screen and SDK version 11 or up), navigation
 * controls are shown in the Action Bar (whether to show tabs or a list depends on the layout).
 * If an Action Bar is not available, a regular image and button are shown in the top area of
 * the screen, emulating an Action Bar.
 */
public class NewsReaderActivity extends FragmentActivity
        implements HeadlinesFragment.OnHeadlineSelectedListener,
                   CompatActionBarNavListener,
                   OnClickListener  {

    // Whether or not we are in dual-pane mode
    boolean mIsDualPane = false;

    // The fragment where the headlines are displayed
    HeadlinesFragment mHeadlinesFragment;

    // The fragment where the article is displayed (null if absent)
    ArticleFragment mArticleFragment;

    // The news category and article index currently being displayed
    int mCatIndex = 0;
    int mArtIndex = 0;
    NewsCategory mCurrentCat;

    // List of category titles
    final String CATEGORIES[] = { "Top Stories", "Politics", "Economy", "Technology" };

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main_layout);

        // find our fragments
        mHeadlinesFragment = (HeadlinesFragment) getSupportFragmentManager().findFragmentById(
                R.id.headlines);
        mArticleFragment = (ArticleFragment) getSupportFragmentManager().findFragmentById(
                R.id.article);

        // Determine whether we are in single-pane or dual-pane mode by testing the visibility
        // of the article view.
        View articleView = findViewById(R.id.article);
        mIsDualPane = articleView != null && articleView.getVisibility() == View.VISIBLE;

        // Register ourselves as the listener for the headlines fragment events.
        mHeadlinesFragment.setOnHeadlineSelectedListener(this);

        // Set up the Action Bar (or not, if one is not available)
        int catIndex = savedInstanceState == null ? 0 : savedInstanceState.getInt("catIndex", 0);
        setUpActionBar(mIsDualPane, catIndex);

        // Set up headlines fragment
        mHeadlinesFragment.setSelectable(mIsDualPane);
        restoreSelection(savedInstanceState);

        // Set up the category button (shown if an Action Bar is not available)
        Button catButton = (Button) findViewById(R.id.categorybutton);
        if (catButton != null) {
            catButton.setOnClickListener(this);
        }
    }

    /** Restore category/article selection from saved state. */
    void restoreSelection(Bundle savedInstanceState) {
        if (savedInstanceState != null) {
            setNewsCategory(savedInstanceState.getInt("catIndex", 0));
            if (mIsDualPane) {
                int artIndex = savedInstanceState.getInt("artIndex", 0);
                mHeadlinesFragment.setSelection(artIndex);
                onHeadlineSelected(artIndex);
            }
        }
    }

    @Override
    public void onRestoreInstanceState(Bundle savedInstanceState) {
        restoreSelection(savedInstanceState);
    }

    /** Sets up Action Bar (if present).
     *
     * @param showTabs whether to show tabs (if false, will show list).
     * @param selTab the selected tab or list item.
     */
    public void setUpActionBar(boolean showTabs, int selTab) {
        if (Build.VERSION.SDK_INT < 11) {
            // No action bar for you!
            // But do not despair. In this case the layout includes a bar across the
            // top that looks and feels like an action bar, but is made up of regular views.
            return;
        }

        android.app.ActionBar actionBar = getActionBar();
        actionBar.setDisplayShowTitleEnabled(false);

        // Set up a CompatActionBarNavHandler to deliver us the Action Bar nagivation events
        CompatActionBarNavHandler handler = new CompatActionBarNavHandler(this);
        if (showTabs) {
            actionBar.setNavigationMode(android.app.ActionBar.NAVIGATION_MODE_TABS);
            int i;
            for (i = 0; i < CATEGORIES.length; i++) {
                actionBar.addTab(actionBar.newTab().setText(CATEGORIES[i]).setTabListener(handler));
            }
            actionBar.setSelectedNavigationItem(selTab);
        }
        else {
            actionBar.setNavigationMode(android.app.ActionBar.NAVIGATION_MODE_LIST);
            SpinnerAdapter adap = new ArrayAdapter<String>(this, R.layout.actionbar_list_item,
                    CATEGORIES);
            actionBar.setListNavigationCallbacks(adap, handler);
        }

        // Show logo instead of icon+title.
        actionBar.setDisplayUseLogoEnabled(true);
    }

    @Override
    public void onStart() {
        super.onStart();
        setNewsCategory(0);
    }

    /** Sets the displayed news category.
     *
     * This causes the headlines fragment to be repopulated with the appropriate headlines.
     */
    void setNewsCategory(int categoryIndex) {
        mCatIndex = categoryIndex;
        mCurrentCat = NewsSource.getInstance().getCategory(categoryIndex);
        mHeadlinesFragment.loadCategory(categoryIndex);

        // If we are displaying the article on the right, we have to update that too
        if (mIsDualPane) {
            mArticleFragment.displayArticle(mCurrentCat.getArticle(0));
        }

        // If we are displaying a "category" button (on the ActionBar-less UI), we have to update
        // its text to reflect the current category.
        Button catButton = (Button) findViewById(R.id.categorybutton);
        if (catButton != null) {
            catButton.setText(CATEGORIES[mCatIndex]);
        }
    }

    /** Called when a headline is selected.
     *
     * This is called by the HeadlinesFragment (via its listener interface) to notify us that a
     * headline was selected in the Action Bar. The way we react depends on whether we are in
     * single or dual-pane mode. In single-pane mode, we launch a new activity to display the
     * selected article; in dual-pane mode we simply display it on the article fragment.
     *
     * @param index the index of the selected headline.
     */
    @Override
    public void onHeadlineSelected(int index) {
        mArtIndex = index;
        if (mIsDualPane) {
            // display it on the article fragment
            mArticleFragment.displayArticle(mCurrentCat.getArticle(index));
        }
        else {
            // use separate activity
            Intent i = new Intent(this, ArticleActivity.class);
            i.putExtra("catIndex", mCatIndex);
            i.putExtra("artIndex", index);
            startActivity(i);
        }
    }

    /** Called when a news category is selected.
     *
     * This is called by our CompatActionBarNavHandler in response to the user selecting a
     * news category in the Action Bar. We react by loading and displaying the headlines for
     * that category.
     *
     * @param catIndex the index of the selected news category.
     */
    @Override
    public void onCategorySelected(int catIndex) {
        setNewsCategory(catIndex);
    }

    /** Save instance state. Saves current category/article index. */
    @Override
    protected void onSaveInstanceState(Bundle outState) {
        outState.putInt("catIndex", mCatIndex);
        outState.putInt("artIndex", mArtIndex);
        super.onSaveInstanceState(outState);
    }

    /** Called when news category button is clicked.
     *
     * This is the button that we display on UIs that don't have an action bar. This button
     * calls up a list of news categories and switches to the given category.
     */
    @Override
    public void onClick(View v) {
        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setTitle("Select a Category");
        builder.setItems(CATEGORIES, new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                setNewsCategory(which);
            }
        });
        AlertDialog d = builder.create();
        d.show();
    }
}