您当前的位置: 二维码扫描的实现，简单的来说可以分三步走：“成像”、“截图”与“识别”。
UWP开发中，最常用的媒体工具非MediaCapture莫属了，下面就来简单介绍一下如何利用MediaCapture来实现扫描和截图并且利用Zxing识别二维码，以及会遇到的问题和需要注意的地方。
1. 初始化与成像
1 private async void InitMediaCaptureAsync() 2 { 3 //寻找后置摄像头 4 var allVideoDevices = await DeviceInformation.FindAllAsync(DeviceClass.VideoCapture); 5 var cameraDevice = allVideoDevices.FirstOrDefault(x => x.EnclosureLocation != null && x.EnclosureLocation.Panel == Windows.Devices.Enumeration.Panel.Back); 6 7 if (cameraDevice == null) 8 { 9 Debug.WriteLine("No camera device found!"); 10 11 return; 12 } 13 14 var settings = new MediaCaptureInitializationSettings 15 { 16 StreamingCaptureMode = StreamingCaptureMode.Video, 17 //必须，否则截图的时候会很卡很慢 18 PhotoCaptureSource = PhotoCaptureSource.VideoPreview, 19 VideoDeviceId = cameraDevice.Id 20 }; 21 22 _mediaCapture = new MediaCapture(); 23 24 try 25 { 26 await _mediaCapture.InitializeAsync(settings); 27 _initialized = true;//初始化成功 28 } 29 catch (UnauthorizedAccessException) 30 { 31 Debug.WriteLine("The app was denied access to the camera"); 32 } 33 catch (Exception ex) 34 { 35 Debug.WriteLine("Exception when initializing MediaCapture with {0}: {1}", cameraDevice.Id, ex.ToString()); 36 } 37 38 if (_initialized) 39 { 40 var focusControl = _mediaCapture.VideoDeviceController.FocusControl; 41 42 if (focusControl.Supported) 43 { 44 var focusSettings = new FocusSettings() 45 { 46 Mode = focusControl.SupportedFocusModes.FirstOrDefault(f => f == FocusMode.Continuous), 47 DisableDriverFallback = true, 48 AutoFocusRange = focusControl.SupportedFocusRanges.FirstOrDefault(f => f == AutoFocusRange.FullRange), 49 Distance = focusControl.SupportedFocusDistances.FirstOrDefault(f => f == ManualFocusDistance.Nearest) 50 }; 51 52 //设置聚焦，最好使用FocusMode.Continuous，否则影响截图会很模糊，不利于识别 53 focusControl.Configure(focusSettings); 54 } 55 56 captureElement.Source = _mediaCapture; 57 captureElement.FlowDirection = FlowDirection.LeftToRight; 58 59 try 60 { 61 await _mediaCapture.StartPreviewAsync(); 62 _previewing = true; 63 } 64 catch (Exception ex) 65 { 66 Debug.WriteLine("Exception when starting the preview: {0}", ex.ToString()); 67 } 68 69 if (_previewing) 70 { 71 try 72 { 73 if (_mediaCapture.VideoDeviceController.FlashControl.Supported) 74 { 75 //关闭闪光灯 76 _mediaCapture.VideoDeviceController.FlashControl.Enabled = false; 77 } 78 } 79 catch 80 { 81 } 82 83 if (focusControl.Supported) 84 { 85 //开始聚焦 86 await focusControl.FocusAsync(); 87 } 88 } 89 } 90 }
2. 截图与识别
1 private void InitTimer() 2 { 3 _timer = new DispatcherTimer(); 4 //每50毫秒截一次图 5 _timer.Interval = TimeSpan.FromMilliseconds(50); 6 _timer.Tick += _timer_Tick; 7 _timer.Start(); 8 }
1 private async void _timer_Tick(object sender, object e) 2 { 3 using (var stream = new InMemoryRandomAccessStream()) 4 { 5 var previewProperties = _mediaCapture.VideoDeviceController.GetMediaStreamProperties(MediaStreamType.VideoPreview) as VideoEncodingProperties; 6 //将截图写入内存流中 7 await _mediaCapture.CapturePhotoToStreamAsync(ImageEncodingProperties.CreateJpeg(), stream); 8 9 //利用Zxing识别，成功：停止timer；失败：继续 10 var reader = new BarcodeReader(); 11 var bitmapWriteable = new WriteableBitmap((int)previewProperties.Width, (int)previewProperties.Height); 12 bitmapWriteable.SetSource(stream); 13 var result = reader.Decode(bitmapWriteable); 14 15 if (!string.IsNullOrEmpty(result.Text)) 16 { 17 _timer.Stop(); 18 } 19 } 20 }
这里顺便说一下如何安装Zxing，打开nuget管理器 命令窗口输入 Install-Package ZXing.Net ，回车; 关于Zxing如何使用，到网上搜索一下有很多教程，这里不再赘述
3. 问题与优化
A） 截图有响声
使用CapturePhotoToStreamAsync来截取图片有的时候会有“咔擦咔擦”声，很影响用户体验，最理想的做法是找到一种能从视频流中直接截取图片的方法，在这里不得不说一句MediaCapture真的真的很强大，MediaCapture给我们提供了直接从视频流中取出其中一帧的方法GetPreviewFrameAsync，于是我把代码进行了如下修改，即流畅又没有烦人的“咔擦咔擦”声
1 private async void _timer_Tick(object sender, object e) 2 { 3 var previewProperties = _mediaCapture.VideoDeviceController.GetMediaStreamProperties(MediaStreamType.VideoPreview) as VideoEncodingProperties; 4 5 using (var videoFrame = new VideoFrame(BitmapPixelFormat.Rgba8, (int)previewProperties.Width, (int)previewProperties.Height)) 6 { 7 using (var currentFrame = await _mediaCapture.GetPreviewFrameAsync(videoFrame)) 8 { 9 using (var previewFrame = currentFrame.SoftwareBitmap) 10 { 11 var buffer = new Windows.Storage.Streams.Buffer((uint)(4 * previewFrame.PixelWidth * previewFrame.PixelHeight)); 12 previewFrame.CopyToBuffer(buffer); 13 14 using (var stream = buffer.AsStream().AsRandomAccessStream()) 15 { 16 //利用Zxing识别，成功：停止timer；失败：继续 17 var reader = new BarcodeReader(); 18 var bitmapWriteable = new WriteableBitmap((int)previewProperties.Width, (int)previewProperties.Height); 19 bitmapWriteable.SetSource(stream); 20 var result = reader.Decode(bitmapWriteable); 21 22 if (!string.IsNullOrEmpty(result.Text)) 23 { 24 _timer.Stop(); 25 } 26 } 27 } 28 } 29 } 30 }
顺便提一下记得要使用如下两个命名空间
using System.IO; using System.Runtime.InteropServices.WindowsRuntime;
否则无法实现buffer.AsStream().AsRandomAccessStream()
B） 连续聚焦
并不是所有机型都支持连续聚焦的（FocusMode.Continuous），这个时候只能自己实现间断性持续聚焦了
C） 截图之后图片处理
有的时候为了实现一些功能（比如说扫描框）或者提高识别率，我们需要对截取出来的图片进行一些二次处理，或剪裁或缩放或旋转，我们可以使用BitmapDecoder和BitmapEncoder来实现
using (var stream = buffer.AsStream().AsRandomAccessStream()) { var decoder = await BitmapDecoder.CreateAsync(BitmapDecoder.JpegDecoderId, stream); var destStream = new InMemoryRandomAccessStream(); var encoder = await BitmapEncoder.CreateForTranscodingAsync(destStream, decoder); //剪裁 encoder.BitmapTransform.Bounds = new BitmapBounds() { X = 0, Y = 0, Width = 100, Height = 100 }; //缩放 encoder.BitmapTransform.ScaledWidth = 100; encoder.BitmapTransform.ScaledHeight = 100; //旋转 encoder.BitmapTransform.Rotation = BitmapRotation.Clockwise90Degrees; await encoder.FlushAsync(); await destStream.FlushAsync();
}
D） 挂起和唤醒
另外值得注意的是，程序在Suspending和Resuming还有Activated时出现的一系列状态转换，这时候很容易引起bug，需要处理好避免crash。
4. 最后
识别出来的字符串处理一般也就超链接和普通文本两种，当然也可以增加条码扫描功能，识别出的是编码，不管怎样，大家可以根据项目具体需求做相应的处理。
- 1楼郑明
- 学习了。。