docs/html/training/basics/network-ops/data-saver.jd

page.title=Optimizing Network Data Usage
parent.title=Performing Network Operations
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@jd:body

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<h2>This lesson teaches you to</h2>
<ol>
  <li><a href="#status">Check Data-Saver Preferences</a>
  <ul>
     <li><a href="#request-whitelist">Request whitelist permissions</a></li>
  </ul>
  </li>
  <li><a href="#monitor-changes">Monitor Changes to Data Saver Preferences</a></li>
  <li><a href="#testing">Test with Android Debug Bridge Commands</a></li>
</ol>

</div>
</div>

<p>
  Over the life of a smartphone, the cost of a cellular data plan can easily
  exceed the cost of the device itself. From Android 7.0 (API level 24),
  users users can enable Data Saver on a device-wide basis in order
  optimize their device's data usage, and use less data. This ability
  is especially useful when roaming, near the end of the billing cycle,
  or for a small prepaid data pack.
</p>

<p>
  When a user enables Data Saver in <strong>Settings</strong> and the device is
  on a metered network, the system blocks background data usage and signals
  apps to use less data in the foreground wherever possible. Users can
  whitelist specific apps to allow background metered data usage even when Data
  Saver is turned on.
</p>

<p>
  The N Developer Preview extends the {@link android.net.ConnectivityManager}
  API to provide apps with a way to <a href="#status">retrieve the user’s Data
  Saver preferences</a> and <a href="#monitor-changes">monitor preference
  changes</a>. It is considered good practice for apps to check whether the
  user has enabled Data Saver and make an effort to limit foreground and
  background data usage.
</p>

<h2 id="status">
  Checking Data Saver Preferences
</h2>

<p>
  In the N Developer Preview, apps can use the {@link
  android.net.ConnectivityManager} API to determine what data usage
  restrictions are being applied. The {@code getRestrictBackgroundStatus()}
  method returns one of the following values:
</p>

<dl>
  <dt>
    {@code RESTRICT_BACKGROUND_STATUS_DISABLED}
  </dt>

  <dd>
    Data Saver is disabled.
  </dd>

  <dt>
    {@code RESTRICT_BACKGROUND_STATUS_ENABLED}
  </dt>

  <dd>
    The user has enabled Data Saver for this app. Apps should make an effort to limit data
    usage in the foreground and gracefully handle restrictions to background
    data usage.
  </dd>

  <dt>
    {@code RESTRICT_BACKGROUND_STATUS_WHITELISTED}
  </dt>

  <dd>
    The user has enabled Data Saver but the app is whitelisted. Apps should
    still make an effort to limit foreground and background data usage.
  </dd>
</dl>

<p>
  It is considered good practice to limit data usage whenever the device is
  connected to a metered network, even if Data Saver is disabled or the app
  is whitelisted. The following sample code uses {@link
  android.net.ConnectivityManager#isActiveNetworkMetered
  ConnectivityManager.isActiveNetworkMetered()} and {@code
  ConnectivityManager.getRestrictBackgroundStatus()} to determine how much data
  the app should use:
</p>

<pre>
ConnectivityManager connMgr = (ConnectivityManager)
        getSystemService(Context.CONNECTIVITY_SERVICE);
// Checks if the device is on a metered network
if (connMgr.isActiveNetworkMetered()) {
  // Checks user’s Data Saver settings.
  switch (connMgr.getRestrictBackgroundStatus()) {
    case RESTRICT_BACKGROUND_STATUS_ENABLED:
    // Background data usage is blocked for this app. Wherever possible,
    // the app should also use less data in the foreground.

    case RESTRICT_BACKGROUND_STATUS_WHITELISTED:
    // The app is whitelisted. Wherever possible,
    // the app should use less data in the foreground and background.

    case RESTRICT_BACKGROUND_STATUS_DISABLED:
    // Data Saver is disabled. Since the device is connected to a
    // metered network, the app should use less data wherever possible.
  }
} else {
  // The device is not on a metered network.
  // Use data as required to perform syncs, downloads, and updates.
}
</pre>

<h3 id="request-whitelist">
  Requesting whitelist permissions
</h3>

<p>
  If your app needs to use data in the background, it can request whitelist
  permissions by sending a
  <code>Settings.ACTION_IGNORE_BACKGROUND_DATA_RESTRICTIONS_SETTINGS</code>
  intent containing a URI of your app's package name: for example,
  <code>package:MY_APP_ID</code>.
</p>

<p>
  Sending the intent and URI launches the <strong>Settings</strong> app and
  displays data usage settings for your app. The user can then decide whether
  to enable background data for your app. Before you send this intent, it is
  good practice to first ask the user if they want to launch the
  <strong>Settings</strong> app for the purpose of enabling background data
  usage.
</p>

<h2 id="monitor-changes">
  Monitoring Changes to Data Saver Preferences
</h2>

<p>
  Apps can monitor changes to Data Saver preferences by creating a {@link
  android.content.BroadcastReceiver} to listen for {@code
  ConnectivityManager.ACTION_RESTRICT_BACKGROUND_CHANGED} and dynamically
  registering the receiver with {@link android.content.Context#registerReceiver
  Context.registerReceiver()}. When an app receives this broadcast, it should
  <a href="#status">check if the new Data Saver preferences affect its
  permissions</a> by calling {@code
  ConnectivityManager.getRestrictBackgroundStatus()}.
</p>

<p class="note">
  <strong>Note:</strong> The system only sends this broadcast to apps that
  dynamically register for them with {@link
  android.content.Context#registerReceiver Context.registerReceiver()}. Apps
  that register to receive this broadcast in their manifest will not receive
  them.
</p>

<h2 id="testing">
  Testing with Android Debug Bridge Commands
</h2>

<p>
  The <a href="{@docRoot}tools/help/adb.html">Android Debug Bridge (ADB)</a>
  provides a few commands that you can use to test your app in Data Saver
  conditions. You can check and configure network
  permissions or set wireless networks as metered to test your app on unmetered
  networks.
</p>
<dl>
  <dt>
    <code>$ adb shell dumpsys netpolicy</code>
  </dt>

  <dd>
    Generates a report that includes the current global background network
    restriction setting, package UIDs currently on a whitelist, and the network
    permissions of other known packages.
  </dd>

  <dt>
    <code>$ adb shell cmd netpolicy</code>
  </dt>

  <dd>
    Displays a full list of Network Policy Manager (netpolicy) commands.
  </dd>

  <dt>
    <code>$ adb shell cmd netpolicy set restrict-background
    &lt;boolean&gt;</code>
  </dt>

  <dd>
    Enables or disables Data Saver mode when passing <code>true</code> or
    <code>false</code>, respectively.
  </dd>

  <dt>
    <code>$ adb shell cmd netpolicy add restrict-background-whitelist
    &lt;UID&gt;</code>
  </dt>

  <dd>
    Adds the specified package UID to the whitelist to allow background metered
    data usage.
  </dd>

  <dt>
    <code>$ adb shell cmd netpolicy remove restrict-background-whitelist
    &lt;UID&gt;</code>
  </dt>

  <dd>
    Removes the specified package UID from the whitelist to block background
    metered data usage while Data Saver is enabled.
  </dd>

  <dt>
    <code>$ adb shell cmd netpolicy list wifi-networks</code>
  </dt>

  <dd>
    Lists all wifi networks, displaying whether they're metered.
  </dd>


  <dt>
    <code>$  adb shell cmd netpolicy set metered-network &lt;WIFI_SSID&gt;
      true</code>
  </dt>

  <dd>
    Sets wifi with the specified SSID as metered, allowing you to simulate a
    metered network on an unmetered network.
  </dd>
</dl>