Android应用程式上的相机无法正常运作

Question

我是Android新手，目前正在开发一款具有捕获条形码功能的应用。但是，它不能正常工作。我只能看到黑色的沥青。我不知道Google API版本是否有任何问题。非常感谢您的帮助

这是build.gradle

android {
compileSdkVersion 28
defaultConfig {
    applicationId "com.example.pointrewarding"
    minSdkVersion 15
    targetSdkVersion 28
    versionCode 1
    versionName "1.0"
    testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    vectorDrawables.useSupportLibrary true


}
buildTypes {
    release {
        minifyEnabled false
        proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
    }
}}


dependencies {
implementation fileTree(dir: 'libs', include: ['*.jar'])
implementation 'com.android.support:appcompat-v7:28.0.0'
implementation 'com.android.support.constraint:constraint-layout:1.1.3'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'com.android.support.test:runner:1.0.2'
androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
implementation 'com.google.zxing:core:3.2.1'
implementation 'com.journeyapps:zxing-android-embedded:3.2.0@aar'
implementation 'com.google.android.gms:play-services-vision:17.0.2' }

这是我的代码

    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_scan_qr);

    surfaceView = (SurfaceView) findViewById(R.id.cameraPreview);
    txtResult = (TextView)findViewById(R.id.txtResult);

    barcodeDetector = new BarcodeDetector.Builder(this)
            .setBarcodeFormats(Barcode.QR_CODE)
            .build();

    cameraSource = new CameraSource.Builder(this, barcodeDetector)
            .setRequestedPreviewSize(640, 480)
            .build();

    // add event
    surfaceView.getHolder().addCallback(new SurfaceHolder.Callback() {
        @Override
        public void surfaceCreated(SurfaceHolder holder) {
            if (ActivityCompat.checkSelfPermission(getApplicationContext(), 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;
            }
            try {
                cameraSource.start(holder);
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        @Override
        public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {

        }

        @Override
        public void surfaceDestroyed(SurfaceHolder holder) {
            cameraSource.stop();
        }
    });

}

这是条形码检测器并会振动

        barcodeDetector.setProcessor(new Detector.Processor<Barcode>() {
        @Override
        public void release() {

        }

        @Override
        public void receiveDetections(Detector.Detections<Barcode> detections) {
            final SparseArray<Barcode> qrCodes = detections.getDetectedItems();
            if(qrCodes.size() != 0 )
            {
                txtResult.post(new Runnable() {
                    @Override
                    public void run() {
                        Vibrator vibrator = (Vibrator)getApplicationContext().getSystemService(Context.VIBRATOR_SERVICE);
                        vibrator.vibrate(1000);
                        txtResult.setText(qrCodes.valueAt(0).displayValue);

                    }
                });
            }
        }
    });