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 MediaCaptureInitializationSettings15 {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.Id20 };21 22 _mediaCapture = new MediaCapture();23 24 try25 {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 try60 {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 try72 {73 if (_mediaCapture.VideoDeviceController.FlashControl.Supported)74 {75 //关闭闪光灯76 _mediaCapture.VideoDeviceController.FlashControl.Enabled = false;77 }78 }79 catch80 {81 }82 83 if (focusControl.Supported)84 {85 //开始聚焦86 await focusControl.FocusAsync();87 }88 }89 }90 }View Code
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 }View Code
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 }View Code
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 }View Code
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。
原标题：UWP中二维码扫描如何实现及问题
关键词：
我知道了 