电池充电状态始终为空

Question

在关注用于监控电池状态变化的Android文档时，我遇到了这个问题：

<receiver android:name=".PowerConnectionReceiver">
  <intent-filter>
    <action android:name="android.intent.action.ACTION_POWER_CONNECTED"/>
    <action android:name="android.intent.action.ACTION_POWER_DISCONNECTED"/>
  </intent-filter>
</receiver>

据说，这允许您通过清单注册BroadcastReceiver以更改电池状态。在接收器中你可以这样做。

public class PowerConnectionReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        int status = intent.getIntExtra(BatteryManager.EXTRA_STATUS, -1);
        boolean isCharging = status == BatteryManager.BATTERY_STATUS_CHARGING ||
                            status == BatteryManager.BATTERY_STATUS_FULL;

        int chargePlug = intent.getIntExtra(BatteryManager.EXTRA_PLUGGED, -1);
        boolean usbCharge = chargePlug == BatteryManager.BATTERY_PLUGGED_USB;
        boolean acCharge = chargePlug == BatteryManager.BATTERY_PLUGGED_AC;
    }
}

但是，虽然我可以在发送此广播时获得电池电量，但Batterymanger.EXTRA_STATUS额外的似乎总是为空。 这是文档中的错误还是我做错了什么？