手电筒无法在 Android 5.1 上启动

我想写一个手电筒。这段代码结果出来了，但是由于某些原因它不能在 Android 5.1 上运行。我在我的 Galaxy Grand Prime 手机上检查了它。

public class MainActivity extends AppCompatActivity {

    private ImageButton btnSwitch = null;
    private Camera camera = null;
    private boolean isFlashOn; //булева переменная для определения включен ли фонарик
    private boolean hasFlash; //переменная для определения есть ли вообще фонарик
    private Camera.Parameters params;
    private CameraManager mCameraManager;
    private String mCameraId;
    private MediaPlayer mp;
    private RelativeLayout activity_main;

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

        activity_main = (RelativeLayout) findViewById(R.id.activity_main);
        btnSwitch = (ImageButton) findViewById(R.id.btnOnOff);

        isFlashOn = false;

        //найти камеру
        hasFlash = getApplicationContext().getPackageManager().hasSystemFeature(PackageManager.FEATURE_CAMERA_FLASH);

        if (!hasFlash) {
            errorDialog();
        }

        getCamera();

        btnSwitch.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (isFlashOn) {
                    turnOff();
                } else {
                    turnOn();
                }
            }
        });
    }

    //Получаем камеру устройства
    public void getCamera() {
        if (Build.VERSION.SDK_INT >= 21) {
            mCameraManager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
            try {
                mCameraId = mCameraManager.getCameraIdList()[0];
            } catch (Exception ex) {
                ex.printStackTrace();
            }
        } else {
            if (camera == null) {
                try {
                    camera = Camera.open();
                    camera.getParameters();
                } catch (RuntimeException ex) {
                    ex.printStackTrace();
                }
            }
        }
    }

    public void turnOff() {
        if (isFlashOn) {
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
                try {
                    mCameraManager.setTorchMode(mCameraId, false);
                    isFlashOn = false;
                    playOnOffSound();
                    btnSwitch.setImageResource(R.drawable.button_off);
                    activity_main.setBackgroundResource(R.drawable.bg_off);
                } catch (Exception ex) {
                    ex.printStackTrace();
                }
            } else {
                if (camera == null || params == null) {
                    return;
                }
                params = camera.getParameters();
                params.setFlashMode(Camera.Parameters.FLASH_MODE_OFF);
                camera.setParameters(params);
                camera.stopPreview();
                isFlashOn = false;
                playOnOffSound();
                btnSwitch.setImageResource(R.drawable.button_off);
                activity_main.setBackgroundResource(R.drawable.bg_off);
            }
        }
    }

    public void turnOn() {
        if (!isFlashOn) {
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
                try {
                    mCameraManager.setTorchMode(mCameraId, true);
                    playOnOffSound();
                    isFlashOn = true;
                    btnSwitch.setImageResource(R.drawable.button_on);
                    activity_main.setBackgroundResource(R.drawable.bg_on);
                } catch (Exception ex) {
                    ex.printStackTrace();
                }
            } else {
                if (camera == null || params == null) {
                    return;
                }
                params = camera.getParameters();
                params.setFlashMode(Camera.Parameters.FLASH_MODE_TORCH);
                camera.setParameters(params);
                camera.startPreview();
                playOnOffSound();
                btnSwitch.setImageResource(R.drawable.button_on);
                activity_main.setBackgroundResource(R.drawable.bg_on);
                isFlashOn = true;
            }
        }
    }

    private void playOnOffSound(){
        mp = MediaPlayer.create(this, R.raw.flash_sound);
        mp.setOnCompletionListener(new MediaPlayer.OnCompletionListener() {
            @Override
            public void onCompletion(MediaPlayer mp) {
                mp.release();
            }
        });
        mp.start();
    }

    @Override
    protected void onStop() {
        super.onStop();
        if(isFlashOn){
            turnOff();
        }
    }

    @Override
    protected void onPause() {
        super.onPause();
        if(isFlashOn){
            turnOff();
        }
    }

    @Override
    protected void onResume() {
        super.onResume();
        if(isFlashOn){
            turnOn();
        }
    }

    public void errorDialog() {
        //создаем диалоговое окно
        AlertDialog dialog = new AlertDialog.Builder(MainActivity.this).create();
        dialog.setTitle("Ошибка!");
        dialog.setMessage("Ваше устройство не поддерживает работу со вспышкой.");
        dialog.setButton("OK", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialogInterface, int i) {
                finish();
            }
        });

        dialog.show();
        return;
    }
}

我在清单中写了以下内容

<uses-permission android:name="android.permission.CAMERA" />
<uses-permission android:name="android.permission.FLASHLIGHT" />
<uses-feature android:name="android.hardware.camera" />
<uses-feature android:name="android.hardware.camera.flash" />
<uses-feature android:name="android.hardware.camera2"/>

据我了解，由于条件原因，它不起作用

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M)

但如果我改为这样写条件

if (Build.VERSION.SDK_INT >= 21)

然后在这个地方发誓

mCameraManager.setTorchMode(mCameraId, false);

调用需要 API 级别 23（当前最小值为 14）：android.hardware.camera2.CameraManager#setTorchMode less... (Ctrl+F1)

在 Android 6 上没问题