Smaple - NetworkUsage

Android Training Link

• Downloads an XML feed from StackOverflow.com for the most recent posts tagged "android".
• Parses the XML feed, combines feed elements with HTML markup, and displays the resulting HTML in the UI.
• Lets users control their network data usage through a settings UI. Users can choose to fetch the feed when any network connection is available, or only when a Wi-Fi connection is available.
• Detects when there is a change in the device's connection status and responds accordingly. For example, if the device loses its network connection, the app will not attempt to download the feed.

1. Manifest

• Permissions
  1. INTERNET
  2. ACCESS_NETWORK_STATE
• Activity

<activity android:label="SettingsActivity" android:name=".SettingsActivity">
     <intent-filter>
        <action android:name="android.intent.action.MANAGE_NETWORK_USAGE" />
        <category android:name="android.intent.category.DEFAULT" />
     </intent-filter>
</activity>

2. SettingsActivity extends PreferenceActivity

implements OnSharedPreferenceChangeListener

• onCreate()

// Loads the XML preferences file.
addPreferencesFromResource(R.xml.preferences);

• onResume()

// Registers a callback to be invoked whenever a user changes a preference.
getPreferenceScreen().getSharedPreferences().registerOnSharedPreferenceChangeListener(this);

• onPause()

// It's best practice to unregister listeners when your app isn't using them to cut down on
// unnecessary system overhead. You do this in onPause().
getPreferenceScreen()
.getSharedPreferences().unregisterOnSharedPreferenceChangeListener(this);

• overrides onSharedPreferenceChanged()

// Sets refreshDisplay to true so that when the user returns to the main
// activity, the display refreshes to reflect the new settings.
NetworkActivity.refreshDisplay = true;

3. preferences.xml

• ListPreference

android:key="listPref"
android:defaultValue="Wi-Fi"
android:entries="@array/listArray"
android:entryValues="@array/listValues"

<resources>
    <string-array name="listArray">
        <item>Only when on Wi-Fi</item>
        <item>On any network</item>
    </string-array>
    <string-array name="listValues">
        <item>Wi-Fi</item>
        <item>Any</item>
    </string-array>
</resources>

• CheckBoxPreference

4. NetworkActivity

• onCreate()

// Register BroadcastReceiver to track connection changes.
IntentFilter filter = new IntentFilter(ConnectivityManager.CONNECTIVITY_ACTION);
receiver = new NetworkReceiver();
this.registerReceiver(receiver, filter);

• onStart()
  Refreshes the display if the network connection and the pref settings allow it.
• updateConnectedFlags()
• loadPage()

if (refreshDisplay) {
        loadPage();
}

• onDestroy()

• unregisterReceiver

• updateConnectedFlags()
  Checks the network connection and sets the wifiConnected and mobileConnected variables accordingly.

ConnectivityManager connMgr =
        (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo activeInfo = connMgr.getActiveNetworkInfo();
if (activeInfo != null && activeInfo.isConnected()) {
    wifiConnected = activeInfo.getType() == ConnectivityManager.TYPE_WIFI;
    mobileConnected = activeInfo.getType() == ConnectivityManager.TYPE_MOBILE;}
 else {
    wifiConnected = false;
    mobileConnected = false;}

• loadPage()

// Uses AsyncTask subclass to download the XML feed from stackoverflow.com.
// This avoids UI lock up. To prevent network operations from
// causing a delay that results in a poor user experience, always perform
// network operations on a separate thread from the UI.
Uses a AsyncTask subclass

new DownloadXmlTask().execute(URL);

• DownloadXmlTask extends AsyncTask<String, Void, String>
• doInBackground(String... urls)

return loadXmlFromNetwork(urls[0]);

• onPostExecute(String result)

myWebView.loadData(result, "text/html", null);

• loadXmlFromNetwork(String urlString)
  // Uploads XML from stackoverflow.com, parses it, and combines it with
  // HTML markup. Returns HTML string.

StackOverflowXmlParser stackOverflowXmlParser = new StackOverflowXmlParser();

Checks whether the user set the preference to include summary text.

SharedPreferences sharedPrefs = PreferenceManager.getDefaultSharedPreferences(this);
boolean pref = sharedPrefs.getBoolean("summaryPref", false);

Downloads & Parses

stream = downloadUrl(urlString);
entries = stackOverflowXmlParser.parse(stream);

StackOverflowXmlParser returns a List (called "entries") of Entry objects.
Each Entry object represents a single post in the XML feed.
This section processes the entries list to combine each entry with HTML markup.
Each entry is displayed in the UI as a link that optionally includes// a text summary.

for (Entry entry : entries) {
    htmlString.append("<p><a href='");
    htmlString.append(entry.link);
    htmlString.append("'>" + entry.title + "</a></p>");
    // If the user set the preference to include summary text,
    // adds it to the display.
    if (pref) {
        htmlString.append(entry.summary);
    }
}

• downloadUrl(String urlString)
  Given a string representation of a URL, sets up a connection and gets an input stream.

• NetworkReceiver extends BroadcastReceiver

overrides onReceive()

// Checks the user prefs and the network connection. Based on the result, decides
// whether
// to refresh the display or keep the current display.
// If the userpref is Wi-Fi only, checks to see if the device has a Wi-Fi connection.
if (WIFI.equals(sPref) && networkInfo != null        
&& networkInfo.getType() == ConnectivityManager.TYPE_WIFI) {    
// If device has its Wi-Fi connection, sets refreshDisplay    
// to true. This causes the display to be refreshed when the user    
// returns to the app.    
refreshDisplay = true;    
Toast.makeText(context, R.string.wifi_connected, Toast.LENGTH_SHORT).show();    
// If the setting is ANY network and there is a network connection    
// (which by process of elimination would be mobile), sets refreshDisplay to true.
} else if (ANY.equals(sPref) && networkInfo != null) {    
refreshDisplay = true;    
// Otherwise, the app can't download content--either because there is no network    
// connection (mobile or Wi-Fi), or because the pref setting is WIFI, and there    
// is no Wi-Fi connection.    
// Sets refreshDisplay to false.
} else {    
refreshDisplay = false;    
Toast.makeText(context, R.string.lost_connection, Toast.LENGTH_SHORT).show();}

5. StackOverflowXmlParser

• Instantiate the Parser.

public List<Entry> parse(InputStream in) throws XmlPullParserException, IOException {
    try {
        XmlPullParser parser = Xml.newPullParser();
        parser.setFeature(XmlPullParser.FEATURE_PROCESS_NAMESPACES, false);
        parser.setInput(in, null);
        parser.nextTag();
        return readFeed(parser);
    } finally {
        in.close();
    }
}

• readFeed()
• Start with tag "feed"
• Look for tag "entry"
• Add "readEntry(parser)" to list<Entry>

private List<Entry> readFeed(XmlPullParser parser) throws XmlPullParserException, IOException {
    List<Entry> entries = new ArrayList<Entry>();
    parser.require(XmlPullParser.START_TAG, ns, "feed");
    while (parser.next() != XmlPullParser.END_TAG) {
        if (parser.getEventType() != XmlPullParser.START_TAG) {
            continue;
        }
        String name = parser.getName();
        // Starts by looking for the entry tag
        if (name.equals("entry")) {
            entries.add(readEntry(parser));
        } else {
            skip(parser);
        }
    }
    return entries;
}

• readEntry()
  Parses the contents of an entry.
  If it encounters a title, summary, or link tag, hands them off to their respective "read" methods for processing. Otherwise, skips the tag.

 private Entry readEntry(XmlPullParser parser) throws XmlPullParserException, IOException {
        parser.require(XmlPullParser.START_TAG, ns, "entry");
        String title = null;
        String summary = null;
        String link = null;
        while (parser.next() != XmlPullParser.END_TAG) {
            if (parser.getEventType() != XmlPullParser.START_TAG) {
                continue;
            }
            String name = parser.getName();
            if (name.equals("title")) {
                title = readTitle(parser);
            } else if (name.equals("summary")) {
                summary = readSummary(parser);
            } else if (name.equals("link")) {
                link = readLink(parser);
            } else {
                skip(parser);
            }
        }
        return new Entry(title, summary, link);
    }

• read method & skip()

private void skip(XmlPullParser parser) throws XmlPullParserException, IOException {
        if (parser.getEventType() != XmlPullParser.START_TAG) {
            throw new IllegalStateException();
        }
        int depth = 1;
        while (depth != 0) {
            switch (parser.next()) {
            case XmlPullParser.END_TAG:
                    depth--;
                    break;
            case XmlPullParser.START_TAG:
                    depth++;
                    break;
            }
        }
    }

if the next tag after a START_TAG isn't a matching END_TAG, it keeps going until it finds the matching END_TAG (as indicated by the value of "depth" being 0).