я не могу загрузить предварительный просмотр камеры в моем приложении, но все остальное работает нормально

Question

комментирование строки "cameraource.start ();" внутри try-улова появляется предварительный просмотр, но я не могу этого сделать, потому что детектор лица не работает. Пожалуйста, помогите ... моя основная активность. java is

package com.example.android.drownsinessdetector;

import android.Manifest;
import android.content.Context;
import android.content.pm.ActivityInfo;
import android.content.pm.PackageManager;
import android.hardware.Camera;
import android.os.Bundle;
import android.support.v4.app.ActivityCompat;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.widget.FrameLayout;
import android.widget.TextView;

import com.google.android.gms.vision.CameraSource;
import com.google.android.gms.vision.Detector;
import com.google.android.gms.vision.MultiProcessor;  
import com.google.android.gms.vision.Tracker;
import com.google.android.gms.vision.face.Face;
import com.google.android.gms.vision.face.FaceDetector;

import java.io.IOException;

public class MainActivity extends AppCompatActivity  {

Camera.CameraInfo cameraInfo = new Camera.CameraInfo();
private static final String TAG = "Video";
int camIdx;

CameraSource cameraSource;
TextView textView;

private Camera mCamera;
private CameraPreview mPreview;




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

    mCamera=getCameraInstance();
    // Create our Preview view and set it as the content of our activity.
    mPreview = new CameraPreview(this, mCamera);
    FrameLayout preview = findViewById(R.id.videoView);
    preview.addView(mPreview);

    Camera.getCameraInfo(camIdx, cameraInfo);
    setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
    mCamera.setDisplayOrientation(90);
    textView = findViewById(R.id.textView);


   createCameraSource();
}

private Camera getCameraInstance() {
    int inf = Camera.CameraInfo.CAMERA_FACING_FRONT;
        Camera c = null;
        try {
            c = Camera.open(inf);
        } catch (Exception e){

        }
        return c;

}

public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback {
    private SurfaceHolder mHolder;
    private Camera mCamera;

    public CameraPreview(Context context, Camera camera) {
        super(context);
        mCamera = camera;
        this.mCamera=camera;

        // Install a SurfaceHolder.Callback so we get notified when the
        // underlying surface is created and destroyed.
        mHolder = getHolder();
        mHolder.addCallback(this);
        // deprecated setting, but required on Android versions prior to 3.0
        mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
        Log.d(TAG,"camera preview class");
    }

    public void surfaceCreated(SurfaceHolder holder) {
        // The Surface has been created, now tell the camera where to draw the preview.
        try {
            mCamera.setPreviewDisplay(holder);
            mCamera.startPreview();
        } catch (IOException e) {
            Log.d(TAG, "Error setting camera preview: " + e.getMessage());
        }
    }

    public void surfaceDestroyed(SurfaceHolder holder) {
        // empty. Take care of releasing the Camera preview in your activity.
    }

    public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
        // If your preview can change or rotate, take care of those events here.
        // Make sure to stop the preview before resizing or reformatting it.

        if (mHolder.getSurface() == null){
            // preview surface does not exist
            return;
        }

        // stop preview before making changes
        try {
            mCamera.stopPreview();
        } catch (Exception e){
            // ignore: tried to stop a non-existent preview
        }

        // set preview size and make any resize, rotate or
        // reformatting changes here

        // start preview with new settings
        try {
            mCamera.setPreviewDisplay(mHolder);
            mCamera.startPreview();

        } catch (Exception e){
            Log.d(TAG, "Error starting camera preview: " + e.getMessage());
        }
    }
}

//This class will use google vision api to detect eyes
private class EyesTracker extends Tracker<Face> {

    private final float THRESHOLD = 0.75f;

    private EyesTracker(){}

    @Override
    public void onUpdate(Detector.Detections<Face> detections, Face face) {
        if (face.getIsLeftEyeOpenProbability() > THRESHOLD || face.getIsRightEyeOpenProbability() > THRESHOLD) {
            Log.i(TAG, "onUpdate: Eyes Detected");
            showStatus("Eyes Detected and open");

        }
        else {

            showStatus("Eyes Detected and closed");
        }
    }

    @Override
    public void onMissing(Detector.Detections<Face> detections) {
        super.onMissing(detections);
        showStatus("Face Not Detected yet!");
    }

    @Override
    public void onDone() {
        super.onDone();
    }
}

private class FaceTrackerFactory implements MultiProcessor.Factory<Face> {

    private FaceTrackerFactory() {

    }

    @Override
    public Tracker<Face> create(Face face) {
        return new EyesTracker();
    }
}

public void createCameraSource() {
    FaceDetector detector = new FaceDetector.Builder(this)
            .setTrackingEnabled(true)
            .setClassificationType(FaceDetector.ALL_CLASSIFICATIONS)
            .setMode(FaceDetector.FAST_MODE)
            .build();
    detector.setProcessor(new MultiProcessor.Builder(new FaceTrackerFactory()).build());

    cameraSource = new CameraSource.Builder(this, detector)
            .setRequestedPreviewSize(1024, 768)
            .setFacing(CameraSource.CAMERA_FACING_FRONT)
            .setRequestedFps(30.0f)
            .build();

    try {
        if (ActivityCompat.checkSelfPermission(this, Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
            // TODO: Consider calling
            //    ActivityCompat#requestPermissions
            // here to request the missing permissions, and then overriding
            //   public void onRequestPermissionsResult(int requestCode, String[] permissions,
            //                                          int[] grantResults)
            // to handle the case where the user grants the permission. See the documentation
            // for ActivityCompat#requestPermissions for more details.
            return;
        }
        cameraSource.start();
    }
    catch (IOException e) {
        e.printStackTrace();
    }

}



public void showStatus(final String message) {
    runOnUiThread(new Runnable() {
        @Override
        public void run() {
            textView.setText(message);
        }
    });
}

@Override
protected void onDestroy() {
    super.onDestroy();

}

}

my макет xml файл

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity"
android:orientation="vertical">

<FrameLayout
    android:id="@+id/videoView"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:layout_weight="0.75"
    android:layout_marginLeft="5dp"
    android:layout_marginTop="5dp"
    android:layout_marginRight="5dp"
    android:orientation="vertical"/>

<EditText
    android:id="@+id/textView"
    android:layout_width="match_parent"
    android:layout_height="63dp"
    android:layout_marginLeft="5dp"
    android:layout_marginTop="5dp"
    android:layout_marginRight="5dp"
    android:layout_marginBottom="15dp"
    android:clickable="false"
    android:text="face_not_found"
    android:textSize="20sp" />

мой файл манифеста

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.android.drownsinessdetector">
<uses-permission android:name="android.permission.CAMERA"/>
<uses-feature android:name="android.hardware.camera" />[enter image description here][1]

<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>
</application>

я могу видеть только черный экран вместо Предварительный просмотр камеры. но детектор глаз и лица работает должным образом. Он показывает сообщение о состоянии, когда глаза открыты или нет. Я также хочу показать предварительный просмотр камеры.