如何通过Android的Mobile Vision API使用CameraSource进行自动对焦？

Question

我正在尝试使用Android Mobile Vision API中的CameraSource类使Camera自动对焦。

我已如下激活自动对焦：

cameraSource = new CameraSource
                .Builder(this, barcodeDetector)
                .setRequestedPreviewSize(640, 480)
                .setAutoFocusEnabled(true)
                .setRequestedFps(24.0f)
                .build();

但是渲染相机的SurfaceView通常是模糊的。

这是我完整的活动代码：

import android.Manifest;
import android.app.Activity;
import android.content.pm.PackageManager;
import android.os.Build;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.v4.app.ActivityCompat;
import android.util.Log;
import android.util.SparseArray;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.widget.TextView;

import com.google.android.gms.vision.CameraSource;
import com.google.android.gms.vision.Detector;
import com.google.android.gms.vision.barcode.Barcode;
import com.google.android.gms.vision.barcode.BarcodeDetector;

import java.io.IOException;
import java.util.Arrays;

public class MainActivity extends Activity {

    private BarcodeDetector barcodeDetector;
    private CameraSource cameraSource;
    private SurfaceView cameraView;
    private TextView barcodeInfo;

    public static int REQUEST_PERMISSION_CAMERA = 1;

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

        cameraView = (SurfaceView) findViewById(R.id.camera_view);
        barcodeInfo = (TextView) findViewById(R.id.code_info);

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

        cameraSource = new CameraSource
                .Builder(this, barcodeDetector)
                .setRequestedPreviewSize(640, 480)
                .setAutoFocusEnabled(true)
                .setRequestedFps(24.0f)
                .build();

        cameraView.getHolder().addCallback(new SurfaceHolder.Callback() {
            @Override
            public void surfaceCreated(SurfaceHolder holder) {
                try {

                    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
                        if (ActivityCompat.checkSelfPermission(MainActivity.this, Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
                            requestPermissions(new String[]{Manifest.permission.CAMERA}, REQUEST_PERMISSION_CAMERA);
                            return;
                        } else {
                            cameraSource.start(cameraView.getHolder());
                        }
                    } else {
                        cameraSource.start(cameraView.getHolder());
                    }
                } catch (IOException ie) {
                    Log.e("CAMERA SOURCE", ie.getMessage());
                }
            }

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

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

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

            @Override
            public void receiveDetections(Detector.Detections<Barcode> detections) {
                final SparseArray<Barcode> barcodes = detections.getDetectedItems();

                if (barcodes.size() != 0) {
                    barcodeInfo.post(new Runnable() {    // Use the post method of the TextView
                        public void run() {
                            barcodeInfo.setText(    // Update the TextView
                                    barcodes.valueAt(0).displayValue
                            );
                        }
                    });
                }
            }
        });

    }

    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        int[] checkValues = new int[1];
        if (requestCode == REQUEST_PERMISSION_CAMERA) {
            if (Arrays.equals(grantResults, checkValues)) {
                if (ActivityCompat.checkSelfPermission(this, Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
                    return;
                }
                try {
                    cameraSource.start(cameraView.getHolder());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        cameraSource.release();
        barcodeDetector.release();
    }
}