有意图地录制视频时，手电筒不能用作后台服务

Question

我正在制作一个Android应用程序，在该应用程序中我要录制视频并以某种方式闪烁闪光灯，从而使人有一种正在拍照的错觉。

我写代码，但是在录制过程中闪光灯熄灭，录制结束后闪光灯开始闪烁。

MainActivity：

public class MainActivity extends AppCompatActivity {

private static final int MY_PERMISSIONS_REQUEST_CAMERA = 555;
private static final int ACTION_TAKE_VIDEO = 1000;
Button btn;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    if (ContextCompat.checkSelfPermission(MainActivity.this, android.Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
        ActivityCompat.requestPermissions(MainActivity.this, new String[]{android.Manifest.permission.CAMERA}, MY_PERMISSIONS_REQUEST_CAMERA);

        Intent serviceIntent = new Intent(this, MyService.class);
        startService(serviceIntent);
        startRecording();
    } else {
        Intent serviceIntent = new Intent(this, MyService.class);
        startService(serviceIntent);

        startRecording();
    }

}

private void startRecording() {
    Intent takeVideoIntent = new Intent(MediaStore.ACTION_VIDEO_CAPTURE);
    takeVideoIntent.putExtra(MediaStore.EXTRA_DURATION_LIMIT, 30);
    takeVideoIntent.putExtra(MediaStore.EXTRA_OUTPUT, Environment.getExternalStorageDirectory().getPath() + "videocapture_example.mp4");

    startActivityForResult(takeVideoIntent, ACTION_TAKE_VIDEO);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.

    return true;
}


@Override
public void onRequestPermissionsResult(int requestCode, String permissions[], int[] grantResults) {
    switch (requestCode) {
        case MY_PERMISSIONS_REQUEST_CAMERA: {
            if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {

            } else {

            }
        }
    }
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    // Check which request we're responding to
    if (requestCode == ACTION_TAKE_VIDEO) {

        // Make sure the request was successful
        if (resultCode == RESULT_OK) {


        }
    }
}

}

MyService.java：服务类

 public class MyService extends Service {
    public static Camera cam = null;
    String value ="10";
    public MyService() {
    }

    @Override
    public IBinder onBind(Intent intent) {
        // TODO: Return the communication channel to the service.
        throw new UnsupportedOperationException("Not yet implemented");
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        onTaskRemoved(intent);
        flashlightSOS();

        Toast.makeText(this, "This is service", Toast.LENGTH_SHORT).show();
        return START_STICKY;
    }

    @Override
    public void onTaskRemoved(Intent rootIntent) {
        Intent restartServiceIntent=new Intent(getApplicationContext(), this.getClass());
        restartServiceIntent.setPackage(getPackageName());
        startService(restartServiceIntent);
        super.onTaskRemoved(rootIntent);
    }
    public void flashlightSOS(){
        while (value.equalsIgnoreCase(value)) {
            flashLightOn();

            new Handler().postDelayed(new Runnable() {
                @Override
                public void run() {

                    flashLightOff();

                }
            }, 5000);


        }

    }
    public void flashLightOn() {

        try {
            if (getPackageManager().hasSystemFeature(
                    PackageManager.FEATURE_CAMERA_FLASH)) {
                cam = Camera.open();
                Camera.Parameters p = cam.getParameters();
                p.setFlashMode(Camera.Parameters.FLASH_MODE_TORCH);
                cam.setParameters(p);
                cam.startPreview();
            }
        } catch (Exception e) {
            e.printStackTrace();
            Toast.makeText(getBaseContext(), "Exception flashLightOn()",
                    Toast.LENGTH_SHORT).show();
        }
    }

    public void flashLightOff() {
        try {
            if (getPackageManager().hasSystemFeature(
                    PackageManager.FEATURE_CAMERA_FLASH)) {
                cam.stopPreview();
                cam.release();
                cam = null;
            }
        } catch (Exception e) {
            e.printStackTrace();
            Toast.makeText(getBaseContext(), "Exception flashLightOff",
                    Toast.LENGTH_SHORT).show();
        }
    }
    }

清单文件：

 <?xml version="1.0" encoding="utf-8"?>
    <manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.sadiariaz.camerasosflash">

    <uses-feature android:name="android.hardware.camera" />

    <uses-permission android:name="android.permission.RECORD_AUDIO" />
    <uses-permission android:name="android.permission.CAMERA" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" `/>`

    <uses-permission android:name="android.permission.FLASHLIGHT" />

    <uses-feature android:name="android.hardware.camera.autofocus" />

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" 
       />
            </intent-filter>
        </activity>

            <service
                android:name=".MyService"
                android:enabled="true"
                android:exported="true"> </service>

            <activity android:name=".VideoCapture"></activity>
        </application>

        </manifest>

我希望它以一种闪烁的方式工作，即有人在录制时正在拍照。