Android 为什么注册ACTION_BATTERY_CHANGED，就能立即得到当前电量

最新推荐文章于 2024-01-19 11:01:39 发布

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最新推荐文章于 2024-01-19 11:01:39 发布

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分类专栏： Android android系统

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本文解析了BatteryService.java中sendIntentLocked方法的工作原理，揭示了如何通过注册BroadcastReceiver监听电池状态变化，并即时获取到最新的电池信息。

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通过对BatteryService.java分析发现。
当系统电量发生变化时，BatteryService通过sendIntentLocked 来告知用户电量发生变化。

    private void sendIntentLocked() {
        //  Pack up the values and broadcast them to everyone
        final Intent intent = new Intent(Intent.ACTION_BATTERY_CHANGED);
        intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY
                | Intent.FLAG_RECEIVER_REPLACE_PENDING);

        int icon = getIconLocked(mBatteryProps.batteryLevel);

        intent.putExtra(BatteryManager.EXTRA_STATUS, mBatteryProps.batteryStatus);
        intent.putExtra(BatteryManager.EXTRA_HEALTH, mBatteryProps.batteryHealth);
        intent.putExtra(BatteryManager.EXTRA_PRESENT, mBatteryProps.batteryPresent);
        intent.putExtra(BatteryManager.EXTRA_LEVEL, mBatteryProps.batteryLevel);
        intent.putExtra(BatteryManager.EXTRA_SCALE, BATTERY_SCALE);
        intent.putExtra(BatteryManager.EXTRA_ICON_SMALL, icon);
        intent.putExtra(BatteryManager.EXTRA_PLUGGED, mPlugType);
        intent.putExtra(BatteryManager.EXTRA_VOLTAGE, mBatteryProps.batteryVoltage);
        intent.putExtra(BatteryManager.EXTRA_TEMPERATURE, mBatteryProps.batteryTemperature);
        intent.putExtra(BatteryManager.EXTRA_TECHNOLOGY, mBatteryProps.batteryTechnology);
        intent.putExtra(BatteryManager.EXTRA_INVALID_CHARGER, mInvalidCharger);

        if (DEBUG) {
            Slog.d(TAG, "Sending ACTION_BATTERY_CHANGED.  level:" + mBatteryProps.batteryLevel +
                    ", scale:" + BATTERY_SCALE + ", status:" + mBatteryProps.batteryStatus +
                    ", health:" + mBatteryProps.batteryHealth +  ", present:" + mBatteryProps.batteryPresent +
                    ", voltage: " + mBatteryProps.batteryVoltage +
                    ", temperature: " + mBatteryProps.batteryTemperature +
                    ", technology: " + mBatteryProps.batteryTechnology +
                    ", AC powered:" + mBatteryProps.chargerAcOnline + ", USB powered:" + mBatteryProps.chargerUsbOnline +
                    ", Wireless powered:" + mBatteryProps.chargerWirelessOnline +
                    ", icon:" + icon  + ", invalid charger:" + mInvalidCharger);
        }

        mHandler.post(new Runnable() {
            @Override
            public void run() {
                ActivityManagerNative.broadcastStickyIntent(intent, null, UserHandle.USER_ALL);
            }
        });
    }

但是系统发生这个广播并不是时刻在发，为什么我们通过

        IntentFilter intentFilter = new IntentFilter(Intent.ACTION_BATTERY_CHANGED);
        mBatteryLowReceiver = new BatteryLowReceiver();
        this.registerReceiver(mBatteryLowReceiver,intentFilter);

就能立即得到系统当前电量呢。
主要是因为系统发送的是驻留广播：

        mHandler.post(new Runnable() {
            @Override
            public void run() {
                ActivityManagerNative.broadcastStickyIntent(intent, null, UserHandle.USER_ALL);
            }
        });

当用户注册ACTION_BATTERY_CHANGED 时，就会收到最近一次改变的intent广播。