1 page.title=Monitoring the Battery Level and Charging State 2 parent.title=Optimizing Battery Life 3 parent.link=index.html 4 5 trainingnavtop=true 6 next.title=Determining and Monitoring the Docking State and Type 7 next.link=docking-monitoring.html 8 9 @jd:body 10 11 <div id="tb-wrapper"> 12 <div id="tb"> 13 14 <h2>This lesson teaches you to</h2> 15 <ol> 16 <li><a href="#DetermineChargeState">Determine the Current Charging State</a></li> 17 <li><a href="#MonitorChargeState">Monitor Changes in Charging State</a></li> 18 <li><a href="#CurrentLevel">Determine the Current Battery Level</a></li> 19 <li><a href="#MonitorLevel">Monitor Significant Changes in Battery Level</a></li> 20 </ol> 21 22 <h2>You should also read</h2> 23 <ul> 24 <li><a href="{@docRoot}guide/components/intents-filters.html">Intents and Intent Filters</a> 25 </ul> 26 27 </div> 28 </div> 29 30 <p>When you're altering the frequency of your background updates to reduce the effect of those 31 updates on battery life, checking the current battery level and charging state is a good place to 32 start.</p> 33 34 <p>The battery-life impact of performing application updates depends on the battery level and 35 charging state of the device. The impact of performing updates while the device is charging over AC 36 is negligible, so in most cases you can maximize your refresh rate whenever the device is connected 37 to a wall charger. Conversely, if the device is discharging, reducing your update rate helps 38 prolong the battery life.</p> 39 40 <p>Similarly, you can check the battery charge level, potentially reducing the frequency of—or 41 even stopping—your updates when the battery charge is nearly exhausted.</p> 42 43 44 <h2 id="DetermineChargeState">Determine the Current Charging State</h2> 45 46 <p>Start by determining the current charge status. The {@link android.os.BatteryManager} 47 broadcasts all battery and charging details in a sticky {@link android.content.Intent} that includes 48 the charging status.</p> 49 50 <p>Because it's a sticky intent, you don't need to register a {@link 51 android.content.BroadcastReceiver}—by simply calling {@code registerReceiver} passing in 52 {@code null} as the receiver as shown in the next snippet, the current battery status intent is 53 returned. You could pass in an actual {@link android.content.BroadcastReceiver} object here, but 54 we'll be handling updates in a later section so it's not necessary.</p> 55 56 <pre>IntentFilter ifilter = new IntentFilter(Intent.ACTION_BATTERY_CHANGED); 57 Intent batteryStatus = context.registerReceiver(null, ifilter);</pre> 58 59 <p>You can extract both the current charging status and, if the device is being charged, whether 60 it's charging via USB or AC charger:<p> 61 62 <pre>// Are we charging / charged? 63 int status = batteryStatus.getIntExtra(BatteryManager.EXTRA_STATUS, -1); 64 boolean isCharging = status == BatteryManager.BATTERY_STATUS_CHARGING || 65 status == BatteryManager.BATTERY_STATUS_FULL; 66 67 // How are we charging? 68 int chargePlug = batteryStatus.getIntExtra(BatteryManager.EXTRA_PLUGGED, -1); 69 boolean usbCharge = chargePlug == BatteryManager.BATTERY_PLUGGED_USB; 70 boolean acCharge = chargePlug == BatteryManager.BATTERY_PLUGGED_AC;</pre> 71 72 <p>Typically you should maximize the rate of your background updates in the case where the device is 73 connected to an AC charger, reduce the rate if the charge is over USB, and lower it 74 further if the battery is discharging.</p> 75 76 77 <h2 id="MonitorChargeState">Monitor Changes in Charging State</h2> 78 79 <p>The charging status can change as easily as a device can be plugged in, so it's important to 80 monitor the charging state for changes and alter your refresh rate accordingly.</p> 81 82 <p>The {@link android.os.BatteryManager} broadcasts an action whenever the device is connected or 83 disconnected from power. It's important to to receive these events even while your app isn't 84 running—particularly as these events should impact how often you start your app in order to 85 initiate a background update—so you should register a {@link 86 android.content.BroadcastReceiver} in your manifest to listen for both events by defining the 87 {@link android.content.Intent#ACTION_POWER_CONNECTED} and {@link 88 android.content.Intent#ACTION_POWER_DISCONNECTED} within an intent filter.</p> 89 90 <pre><receiver android:name=".PowerConnectionReceiver"> 91 <intent-filter> 92 <action android:name="android.intent.action.ACTION_POWER_CONNECTED"/> 93 <action android:name="android.intent.action.ACTION_POWER_DISCONNECTED"/> 94 </intent-filter> 95 </receiver></pre> 96 97 <p>Within the associated {@link android.content.BroadcastReceiver} implementation, you can extract 98 the current charging state and method as described in the previous step.</p> 99 100 <pre>public class PowerConnectionReceiver extends BroadcastReceiver { 101 @Override 102 public void onReceive(Context context, Intent intent) { 103 int status = intent.getIntExtra(BatteryManager.EXTRA_STATUS, -1); 104 boolean isCharging = status == BatteryManager.BATTERY_STATUS_CHARGING || 105 status == BatteryManager.BATTERY_STATUS_FULL; 106 107 int chargePlug = intent.getIntExtra(BatteryManager.EXTRA_PLUGGED, -1); 108 boolean usbCharge = chargePlug == BatteryManager.BATTERY_PLUGGED_USB; 109 boolean acCharge = chargePlug == BatteryManager.BATTERY_PLUGGED_AC; 110 } 111 }</pre> 112 113 114 <h2 id="CurrentLevel">Determine the Current Battery Level</h2> 115 116 <p>In some cases it's also useful to determine the current battery level. You may choose to reduce 117 the rate of your background updates if the battery charge is below a certain level.</p> 118 119 <p>You can find the current battery charge by extracting the current battery level and scale from 120 the battery status intent as shown here:</p> 121 122 <pre>int level = batteryStatus.getIntExtra(BatteryManager.EXTRA_LEVEL, -1); 123 int scale = batteryStatus.getIntExtra(BatteryManager.EXTRA_SCALE, -1); 124 125 float batteryPct = level / (float)scale;</pre> 126 127 128 <h2 id="MonitorLevel">Monitor Significant Changes in Battery Level</h2> 129 130 <p>You can't easily continually monitor the battery state, but you don't need to.</p> 131 132 <p>Generally speaking, the impact of constantly monitoring the battery level has a greater 133 impact on the battery than your app's normal behavior, so it's good practice to only monitor 134 significant changes in battery level—specifically when the device enters or exits a low 135 battery state.</p> 136 137 <p>The manifest snippet below is extracted from the intent filter element within a broadcast 138 receiver. The receiver is triggered whenever the device battery becomes low or exits the low 139 condition by listening for {@link android.content.Intent#ACTION_BATTERY_LOW} and {@link 140 android.content.Intent#ACTION_BATTERY_OKAY}.</p> 141 142 <pre><receiver android:name=".BatteryLevelReceiver"> 143 <intent-filter> 144 <action android:name="android.intent.action.ACTION_BATTERY_LOW"/> 145 <action android:name="android.intent.action.ACTION_BATTERY_OKAY"/> 146 </intent-filter> 147 </receiver></pre> 148 149 <p>It is generally good practice to disable all your background updates when the battery is 150 critically low. It doesn't matter how fresh your data is if the phone turns itself off before you 151 can make use of it.</p> 152 153 <p>In many cases, the act of charging a device is coincident with putting it into a dock. The next 154 lesson shows you how to determine the current dock state and monitor for changes in device 155 docking.</p> 156 157
