java - 重新启动 zbar 条码扫描器示例应用程序时出现黑屏

Question

我正在运行用于条形码扫描的示例代码，但在按下主页按钮后，当我重新启动应用程序时，摄像头无法正常工作，并且出现黑屏。有人明白原因吗？

代码:

public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.main);

        setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);

        autoFocusHandler = new Handler();
        mCamera = getCameraInstance();

        /* Instance barcode scanner */
        scanner = new ImageScanner();
        scanner.setConfig(0, Config.X_DENSITY, 3);
        scanner.setConfig(0, Config.Y_DENSITY, 3);

        mPreview = new CameraPreview(this, mCamera, previewCb, autoFocusCB);
        FrameLayout preview = (FrameLayout)findViewById(R.id.cameraPreview);
        preview.addView(mPreview);

        scanText = (TextView)findViewById(R.id.scanText);

        scanButton = (Button)findViewById(R.id.ScanButton);

        scanButton.setOnClickListener(new OnClickListener() {
                public void onClick(View v) {
                    if (barcodeScanned) {
                        barcodeScanned = false;
                        scanText.setText("Scanning...");
                        mCamera.setPreviewCallback(previewCb);
                        mCamera.startPreview();
                        previewing = true;
                        mCamera.autoFocus(autoFocusCB);
                    }
                }
            });
    }

    public void onPause() {
        super.onPause();
        releaseCamera();
    }

    /** A safe way to get an instance of the Camera object. */
    public static Camera getCameraInstance(){
        Camera c = null;
        try {
            c = Camera.open();
        } catch (Exception e){
        }
        return c;
    }

    private void releaseCamera() {
        if (mCamera != null) {
            previewing = false;
            mCamera.setPreviewCallback(null);
            mPreview.getHolder().removeCallback(mPreview);
            mCamera.release();
            mCamera = null;
        }
    }

    private Runnable doAutoFocus = new Runnable() {
            public void run() {
                if (previewing)
                    mCamera.autoFocus(autoFocusCB);
            }
        };

    PreviewCallback previewCb = new PreviewCallback() {
            public void onPreviewFrame(byte[] data, Camera camera) {
                Camera.Parameters parameters = camera.getParameters();
                Size size = parameters.getPreviewSize();

                Image barcode = new Image(size.width, size.height, "Y800");
                barcode.setData(data);

                int result = scanner.scanImage(barcode);

                if (result != 0) {
                    previewing = false;
                    mCamera.setPreviewCallback(null);
                    mCamera.stopPreview();

                    SymbolSet syms = scanner.getResults();
                    for (Symbol sym : syms) {
                        scanText.setText("barcode result " + sym.getData());
                        barcodeScanned = true;
                    }
                }
            }
        };

    // Mimic continuous auto-focusing
    AutoFocusCallback autoFocusCB = new AutoFocusCallback() {
            public void onAutoFocus(boolean success, Camera camera) {
                autoFocusHandler.postDelayed(doAutoFocus, 1000);
            }
        };

Answer 1

总是成对做这样的事情。如果您在 onPause() 中释放相机，请在 onResume() 中获取并开始预览，而不是在 onCreate() 中。当您回到家时，您的 Activity 将暂停但不会被销毁。所以你释放相机，当你回来时你的 Activity 被恢复。由于除了在 onCreate() 中之外，您永远不会重新初始化相机，所以您看不到预览。