如何在Android Studio中扫描二维码时打开/关闭闪光灯

Question

我已经查看了许多有关此问题和答案，但是在我的情况下它们不起作用。

我正在使用Android Studio开发QR码扫描应用程序。

但这给我一个错误：

“ java.lang.RuntimeException：无法连接到摄像头服务”

谁知道我错了？

这是清单：

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

<!-- Camera Permissions -->
<uses-permission android:name="android.permission.CAMERA" />

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

下面是我的代码：

import android.content.Intent;
import android.content.pm.PackageManager;
import android.hardware.Camera;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.SparseArray;
import android.view.View;
import android.webkit.URLUtil;
import android.widget.Toast;
import com.google.android.gms.vision.barcode.Barcode;
import java.util.List;
import info.androidhive.barcode.BarcodeReader;

public class ScanQRActivity extends AppCompatActivity  implements BarcodeReader.BarcodeReaderListener {

    private boolean isOnFlash = false;
    static Camera camera;
    static Camera.Parameters parameters;

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

        findViewById(R.id.btnLight).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (isOnFlash) {
                    turnOnFlash();
                }
                else {
                    getCamera();
                    turnOffFlash();
                }
            }
        });

        findViewById(R.id.btnBack).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                finish();
            }
        });
    }

    private void getCamera() {
        if (camera == null) {
            try {
                camera = Camera.open();
                parameters = camera.getParameters();
            }
            catch (Exception ex) {
                Toast.makeText(this, ex.toString(), Toast.LENGTH_SHORT).show();
            }
        }
    }

    private void turnOnFlash() {
        if( ! getApplicationContext().getPackageManager().hasSystemFeature(PackageManager.FEATURE_CAMERA_FLASH)) {
            Toast.makeText(this, "Sorry, your device doesn't support flash light!", Toast.LENGTH_LONG).show();
        }

        try {
            parameters.setFlashMode(Camera.Parameters.FLASH_MODE_TORCH);
            camera.setParameters(parameters);
            camera.startPreview();
            isOnFlash = true;
        }
        catch (Exception ex) {
            Toast.makeText(this, ex.toString(), Toast.LENGTH_SHORT).show();
        }
    }

    private void turnOffFlash() {
        try {
            parameters.setFlashMode(Camera.Parameters.FLASH_MODE_OFF);
            camera.setParameters(parameters);
            camera.stopPreview();
            isOnFlash = false;
        }
        catch (Exception ex) {
            Toast.makeText(this, ex.toString(), Toast.LENGTH_SHORT).show();
        }
    }

    @Override
    protected void onStop() {
        super.onStop();
        if (camera != null) {
            camera.release();
            camera = null;
            parameters = null;
        }
    }

    @Override
    public void onScanned(Barcode barcode) {
        gotoResultActivity(barcode.displayValue);
    }

    @Override
    public void onScannedMultiple(List<Barcode> barcodes) {

    }

    @Override
    public void onBitmapScanned(SparseArray<Barcode> sparseArray) {

    }

    @Override
    public void onScanError(String errorMessage) {

    }

    @Override
    public void onCameraPermissionDenied() {

    }

    private void gotoResultActivity(String displayValue) {
        if ( URLUtil.isValidUrl(displayValue) ) {
            Intent intent = new Intent(this, ResultActivity.class);
            Bundle bundle = new Bundle();
            bundle.putString("url", displayValue);
            intent.putExtras(bundle);
            startActivity ( intent );
            finish();
        }
        else {
            Toast.makeText(this, "Invalid Url", Toast.LENGTH_SHORT).show();
        }
    }
}