Get battery level before broadcast receiver responds for Intent.ACTION_BATTERY_CHANGED

问题

I have a broadcast receiver in my program to get react to the battery level like so:

private BroadcastReceiver mBatInfoReceiver = new BroadcastReceiver(){
    @Override
    public void onReceive(Context arg0, Intent intent) {
        int level = intent.getIntExtra(\"level\", 0);
        // do something...
    }
}

    registerReceiver(this.mBatInfoReceiver, 
            new IntentFilter(Intent.ACTION_BATTERY_CHANGED));

However this code has to wait for the battery status to be updated so if you have a GUI element that needs to be set based on the battery level it must wait for a battery event to occur. Is there a way to nudge this to get it working or simply run some code to see what the battery level was on the last broadcast?

回答1:

Is there a way to nudge this to get it working or simply run some code to see what the battery level was on the last broadcast?

You can call registerReceiver() with your IntentFilter and a null BroadcastReceiver to get the last-broadcast Intent. This works because ACTION_BATTERY_CHANGED is a so-called "sticky broadcast", which I describe a bit more in this StackOverflow question-and-answer.

回答2:

This is how to get the battery level without registering a receiver:

Intent batteryIntent = context.getApplicationContext().registerReceiver(null,
                    new IntentFilter(Intent.ACTION_BATTERY_CHANGED));
int rawlevel = batteryIntent.getIntExtra(BatteryManager.EXTRA_LEVEL, -1);
double scale = batteryIntent.getIntExtra(BatteryManager.EXTRA_SCALE, -1);
double level = -1;
if (rawlevel >= 0 && scale > 0) {
    level = rawlevel / scale;
}

It can use a null BroadcastReceiver because of the sticky nature of the broadcast.

It uses the getApplicationContext() trick in case you are in a intent receiver and get the exception:

android.content.ReceiverCallNotAllowedException: IntentReceiver components are not allowed to register to receive intents

回答3:

    public static String batteryLevel(Context context)
    {
        Intent intent  = context.registerReceiver(null, new IntentFilter(Intent.ACTION_BATTERY_CHANGED));   
        int    level   = intent.getIntExtra(BatteryManager.EXTRA_LEVEL, 0);
        int    scale   = intent.getIntExtra(BatteryManager.EXTRA_SCALE, 100);
        int    percent = (level*100)/scale;
        return String.valueOf(percent) + "%";
    }

回答4:

// Put this Code into your MainActivity

private BroadcastReceiver mBatInfoReceiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context c, Intent i) {
        int level = i.getIntExtra("level", 0);
        ProgressBar pb = (ProgressBar) findViewById(R.id.progressbar);
        pb.setProgress(level);
        TextView tv = (TextView) findViewById(R.id.textfield);
        tv.setText("Battery Level: " + Integer.toString(level) + "%");
    }

};

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    registerReceiver(mBatInfoReceiver, new IntentFilter(
            Intent.ACTION_BATTERY_CHANGED));
}

回答5:

I use this method to get the battery level without receiving updates.

public float getMyBatteryLevel() {
        Intent batteryIntent = this.getApplicationContext().registerReceiver(null,
        new IntentFilter(Intent.ACTION_BATTERY_CHANGED));
        return batteryIntent.getIntExtra("level", -1);
}

回答6:

Please be aware, that the intent you get from registerReceiver call

Intent intent  = context.registerReceiver(null, new IntentFilter(Intent.ACTION_BATTERY_CHANGED));

can be null. So please make a check before using the intent, e.g.

if(intent != null){ 
// do your stuff here... 
}

I just got a null pointer exception, causing the app to crash!

来源：https://stackoverflow.com/questions/3661464/get-battery-level-before-broadcast-receiver-responds-for-intent-action-battery-c

标签

android

broadcastreceiver

battery