仅当我的应用程序处于活动状态并且也在后台且未被破坏时，我如何 运行 在后台进行 BLE 扫描？

Question

我的应用程序在后台扫描 BLE 设备，以便在设备停止广播或 RSSI 低于设定限制时向用户发送通知。

但是，我注意到即使我的应用程序已关闭并且不再在后台运行，我的应用程序有时仍会扫描 BLE 设备。我怎样才能让这些后台 BLE 扫描仅在我的应用程序处于活动状态且在后台时才在后台进行？

我目前正在禁用 onDestroy 回调中的扫描，但我读到不推荐这样做，因为其中的代码并不总是被执行。这也是为什么我的应用程序有时仍然会在后台扫描的原因。

下面是 onDestroy 回调和我用来启动或停止扫描的代码。

@Override
public void onDestroy() {
    super.onDestroy();
    scanLeDevice(false); //stop scanning and stop notification from showing when app closed
    try {
        unregisterReceiver(mReceiverOn);
        unregisterReceiver(mReceiverOff);
        //Register or UnRegister your broadcast receiver here

    } catch(IllegalArgumentException e) {

        e.printStackTrace();
    }
    stopService();
    Log.d("lifecycle", "onDestroy: isAppRunning in on destroy");
}

 private void scanLeDevice(final boolean enable) { //need to update to non deprecated code
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M && PackageManager.PERMISSION_GRANTED != getApplicationContext().checkCallingOrSelfPermission(Manifest.permission.ACCESS_FINE_LOCATION))
    {
        Toast.makeText(DeviceScanActivity.this, R.string.location_permission_needed, Toast.LENGTH_SHORT).show();
        requestPermissions(new String[]{Manifest.permission.ACCESS_FINE_LOCATION}, 9); //get fine location, needed for android 10
    }
    else if (enable && !scanRunning) { //starting a scan that is currently not running
        mHandler.postDelayed(new Runnable() {
            @Override
            public void run() { //Stops scanning after a pre-defined scan period. This is required if you are to scan indefinitely
                mBluetoothAdapter.stopLeScan(mLeScanCallback );
                scanRunning = false;
                if(mScanning)
                    mHandler2.postDelayed(new Runnable() {
                        @Override
                        public void run() {
                            scanLeDevice(true);
                        }
                    }, 650);
                invalidateOptionsMenu();
            }
        }, 8000);
        mScanning = true;
        scanRunning = true;
        boolean onScanner = mBluetoothAdapter.startLeScan(uuid, mLeScanCallback);
        Log.d(TAG, "scanLeDevice: onScanner " + onScanner + " isDiscovering " + mBluetoothAdapter.isDiscovering());
    } else if (enable && appNotDestroyed){ //scanRunning is true
        mScanning = true;
        mBluetoothAdapter.startLeScan(uuid, mLeScanCallback);
        Log.d(TAG, "scanLeDevice: mScanning " + mScanning + " isDiscovering " + mBluetoothAdapter.isDiscovering());
    } else { //enable is false
        mScanning = false;
        mBluetoothAdapter.stopLeScan(mLeScanCallback);
        if(!clearHandlerHasRunnable) {
            clearHandlerHasRunnable = true;
            clearHandler.postDelayed(new Runnable() {
                @Override
                public void run() {
                    if (!mScanning)
                        clearUnsavedDevices(mLeDevices);
                    clearHandlerHasRunnable = false;
                }
            }, 3000);
        }
    }
    invalidateOptionsMenu();
    if(!mScanning){ //clear indicators for all cells so that user isn't confused by certain indicators being on/off
        for (int i = 0; i < mLeDevices.size(); i++){
            updateViewScanFor(i);
        }
    }
}

Answer 1

我不再在我的 onPause() 中启动后台扫描，然后在我的主程序中的 onDestroy() 中停止它 activity。

相反，我正在启动一个进行扫描的前台服务。这允许我的应用程序停止服务，因此当我的应用程序被销毁时停止扫描，因为后台没有发生任何事情。