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
private async void InitMediaCaptureAsync()
{
//寻找后置摄像头
var allVideoDevices = await DeviceInformation.FindAllAsync(DeviceClass.VideoCapture);
var cameraDevice = allVideoDevices.FirstOrDefault(x => x.EnclosureLocation != null && x.EnclosureLocation.Panel == Windows.Devices.Enumeration.Panel.Back); if (cameraDevice == null)
{
Debug.WriteLine("No camera device found!"); return;
} var settings = new MediaCaptureInitializationSettings
{
StreamingCaptureMode = StreamingCaptureMode.Video,
//必须，否则截图的时候会很卡很慢
PhotoCaptureSource = PhotoCaptureSource.VideoPreview,
VideoDeviceId = cameraDevice.Id
}; _mediaCapture = new MediaCapture(); try
{
await _mediaCapture.InitializeAsync(settings);
_initialized = true;//初始化成功
}
catch (UnauthorizedAccessException)
{
Debug.WriteLine("The app was denied access to the camera");
}
catch (Exception ex)
{
Debug.WriteLine("Exception when initializing MediaCapture with {0}: {1}", cameraDevice.Id, ex.ToString());
} if (_initialized)
{
var focusControl = _mediaCapture.VideoDeviceController.FocusControl; if (focusControl.Supported)
{
var focusSettings = new FocusSettings()
{
Mode = focusControl.SupportedFocusModes.FirstOrDefault(f => f == FocusMode.Continuous),
DisableDriverFallback = true,
AutoFocusRange = focusControl.SupportedFocusRanges.FirstOrDefault(f => f == AutoFocusRange.FullRange),
Distance = focusControl.SupportedFocusDistances.FirstOrDefault(f => f == ManualFocusDistance.Nearest)
}; //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
focusControl.Configure(focusSettings);
} captureElement.Source = _mediaCapture;
captureElement.FlowDirection = FlowDirection.LeftToRight; try
{
await _mediaCapture.StartPreviewAsync();
_previewing = true;
}
catch (Exception ex)
{
Debug.WriteLine("Exception when starting the preview: {0}", ex.ToString());
} if (_previewing)
{
try
{
if (_mediaCapture.VideoDeviceController.FlashControl.Supported)
{
//关闭闪光灯
_mediaCapture.VideoDeviceController.FlashControl.Enabled = false;
}
}
catch
{
} if (focusControl.Supported)
{
//开始聚焦
await focusControl.FocusAsync();
}
}
}
}
2. 截图与识别
private void InitTimer()
{
_timer = new DispatcherTimer();
//每50毫秒截一次图
_timer.Interval = TimeSpan.FromMilliseconds();
_timer.Tick += _timer_Tick;
_timer.Start();
}
private async void _timer_Tick(object sender, object e)
{
using (var stream = new InMemoryRandomAccessStream())
{
var previewProperties = _mediaCapture.VideoDeviceController.GetMediaStreamProperties(MediaStreamType.VideoPreview) as VideoEncodingProperties;
//将截图写入内存流中
await _mediaCapture.CapturePhotoToStreamAsync(ImageEncodingProperties.CreateJpeg(), stream); //利用Zxing识别，成功：停止timer；失败：继续
var reader = new BarcodeReader();
var bitmapWriteable = new WriteableBitmap((int)previewProperties.Width, (int)previewProperties.Height);
bitmapWriteable.SetSource(stream);
var result = reader.Decode(bitmapWriteable); if (!string.IsNullOrEmpty(result.Text))
{
_timer.Stop();
}
}
}
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
private async void _timer_Tick(object sender, object e)
{
var previewProperties = _mediaCapture.VideoDeviceController.GetMediaStreamProperties(MediaStreamType.VideoPreview) as VideoEncodingProperties; using (var videoFrame = new VideoFrame(BitmapPixelFormat.Rgba8, (int)previewProperties.Width, (int)previewProperties.Height))
{
using (var currentFrame = await _mediaCapture.GetPreviewFrameAsync(videoFrame))
{
using (var previewFrame = currentFrame.SoftwareBitmap)
{
var buffer = new Windows.Storage.Streams.Buffer((uint)( * previewFrame.PixelWidth * previewFrame.PixelHeight));
previewFrame.CopyToBuffer(buffer); using (var stream = buffer.AsStream().AsRandomAccessStream())
{
//利用Zxing识别，成功：停止timer；失败：继续
var reader = new BarcodeReader();
var bitmapWriteable = new WriteableBitmap((int)previewProperties.Width, (int)previewProperties.Height);
bitmapWriteable.SetSource(stream);
var result = reader.Decode(bitmapWriteable); if (!string.IsNullOrEmpty(result.Text))
{
_timer.Stop();
}
}
}
}
}
}
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 = , Y = , Width = , Height = };
//缩放
encoder.BitmapTransform.ScaledWidth = ;
encoder.BitmapTransform.ScaledHeight = ;
//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。
