windows phone 8.1 RT Zxing.net 实施：CapturePhotoToStreamAsync 问题

Question

我正在使用 ZXing.net 创建一个用户控件，用于使用相机将条形码扫描到 Windows Phone 8.1 RT 应用程序中。

条形码解码良好，但在调用 CapturePhotoToStreamAsync 方法时，我在 UI 上冻结，即使它正在等待。执行大约需要 600 毫秒。

我正在模拟器中测试应用程序。

下面的代码在异步方法中执行：

// Preview of the camera    
await _mediaCapture.InitializeAsync(settings);
VideoCapture.Source = _mediaCapture;
VideoCapture.FlowDirection = Windows.UI.Xaml.FlowDirection.LeftToRight;
await _mediaCapture.StartPreviewAsync();

VideoEncodingProperties res = _mediaCapture.VideoDeviceController.GetMediaStreamProperties(MediaStreamType.VideoPreview) as VideoEncodingProperties;
ImageEncodingProperties iep = ImageEncodingProperties.CreateBmp();

iep.Height = res.Height;
iep.Width = res.Width;

var barcodeReader = new BarcodeReader
{
     TryHarder = true,
     AutoRotate = true
};

WriteableBitmap wB = new WriteableBitmap((int)res.Width, (int)res.Height);
while (_result == null)
{
     using (var stream = new InMemoryRandomAccessStream())
     {
        await _mediaCapture.CapturePhotoToStreamAsync(iep, stream);

        stream.Seek(0);
        await wB.SetSourceAsync(stream);

        _result = barcodeReader.Decode(wB);
      }
 }

 await _mediaCapture.StopPreviewAsync();
 //callback to handle result
 ScanCallback(_result.Text);

如何防止 UI 冻结？

Answer 1

当我先用相机拍照（让你对焦在条形码所在的正确位置）然后发送图片进行条形码识别时，我总是能得到更好的结果。

卡顿是因为您尝试不断检查实时提要中的条形码，这在 CPU（尤其是 ARM 设备）上可能很困难

var dialog = new CameraCaptureUI();
StorageFile file = await dialog.CaptureFileAsync(CameraCaptureUIMode.Photo);
var stream = await file.OpenReadAsync();
// initialize with 1,1 to get the current size of the image
var writeableBmp = new WriteableBitmap(1, 1);
writeableBmp.SetSource(stream);
// and create it again because otherwise the WB isn't fully initialized and decoding
// results in a IndexOutOfRange
writeableBmp = new WriteableBitmap(writeableBmp.PixelWidth, writeableBmp.PixelHeight);
stream.Seek(0);
writeableBmp.SetSource(stream);

var result = ScanBitmap(writeableBmp);
string barcode = "";
if (result != null)
{
    barcode = result.Text;
}

这里是 ScanBitmap 方法：

    private Result ScanBitmap(WriteableBitmap writeableBmp)
    {
        var barcodeReader = new BarcodeReader
        {
            Options = new ZXing.Common.DecodingOptions()
            {
                TryHarder = true
            },
            AutoRotate = true
        };
        var result = barcodeReader.Decode(writeableBmp);

        if (result != null)
        {
            CaptureImage.Source = writeableBmp;
        }

        return result;
    }

Answer 2

幸运的是，您无需拍摄照片即可在 Windows Phone 8.1 运行时解码 QRCode/Barcode。这实际上是一个全新的解决方案，但它确实有效：https://github.com/mmaitre314/VideoEffect#realtime-video-analysis-and-qr-code-detection 安装 nuget 包后，您可以轻松实时解码条形码，无需调用 CapturePhotoToStreamAsync。唯一的缺点是您只能针对 ARM。您可以在网站上找到示例代码。或者你可以联系我，我可以把我使用它的项目部分发给你。

windows phone 8.1 RT Zxing.net 实施：CapturePhotoToStreamAsync 问题

windows phone 8.1 RT Zxing.net implementation : issue with CapturePhotoToStreamAsync

c#

zxing

windows-runtime

windows-phone-8.1