WindowsPhone8.1 开发二维码扫描的问题

Question

在WP8.1中解析二维码图片 我采用的是和winrt的方法 

但是遇到了一个问题

1.我采用 CapturePhotoToStorageFileAsync() 将图片保存到本地 在读取的方式 是不会出现问题

   

 try
            {
                while (_result == null)
                {
                    if (!IsBusy)
                    {
                        IsBusy = true;
                       
                        var photoStorageFile = await KnownFolders.PicturesLibrary.CreateFileAsync("qcode.jpg", CreationCollisionOption.ReplaceExisting);
                        await _mediaCapture.CapturePhotoToStorageFileAsync(ImageEncodingProperties.CreateJpeg(), photoStorageFile);

                        var stream = await photoStorageFile.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);
                        _result = ScanBitmap(writeableBmp);
                        await photoStorageFile.DeleteAsync(StorageDeleteOption.PermanentDelete);
                    }
                    if (_result != null)
                    {
                        await _mediaCapture.StopPreviewAsync();
                        VideoCapture.Visibility = Visibility.Collapsed;
                        CaptureImage.Visibility = Visibility.Visible;
                        ScanResult.Text = _result.Text;
                        _timer.Stop();
                        myStoryboard.Stop();
                        imgScan.Visibility = Visibility.Collapsed;
                       
                    }  
                    IsBusy = false;
                 
                }
            }
            catch (Exception ex)
            {
               
                IsBusy = false;
                //Error.Text = ex.Message;
            }

这种方法不会出现问题 

2但是我如果采用CapturePhotoToStreamAsync()直接获取图片流在解析二维码图片就出现了问题

 

try
            {
                while (_result == null)
                {
                   
                    IRandomAccessStream stream = new InMemoryRandomAccessStream();
                    await _mediaCapture.CapturePhotoToStreamAsync(ImageEncodingProperties.CreatePng(), stream);
                    await stream.FlushAsync();
                    stream.Seek(0);
                
                    WriteableBitmap writeableBmp = new WriteableBitmap(640, 480);
                    writeableBmp.SetSource(stream);
                   if (writeableBmp != null)
                   {
                       _result = ScanBitmap(writeableBmp);
                       if (_result != null)
                       {
                           await _mediaCapture.StopPreviewAsync();
                           VideoCapture.Visibility = Visibility.Collapsed;
                           CaptureImage.Visibility = Visibility.Visible;
                           ScanResult.Text = _result.Text;
                           //_timer.Stop();
                           myStoryboard.Stop();
                           imgScan.Visibility = Visibility.Collapsed;
                       }
                   }
                }
            }
            catch (Exception ex)
            {
 
           
            }

我的详细代码地址：http://www.cnblogs.com/fxiaoquan/p/4030836.html

请大家分析一下问什么？

---

爱编程 爱生活