UWP BarcodeScanner 预览：CaptureElement 不显示任何预览

Question

我的 CaptureElements 表现出奇怪的行为。当我将实例化的 MediaCapture 设置为 CaptureElements Source 然后调用 MediaCapture.StartPreviewAsync() 时，CaptureElement 不显示任何内容。

我在 LoginPage 上有一个带有功能性 BarcodeScanner 的应用程序（主应用程序）。 -> 有效！

然后我想将相同的代码复制到 SettingsPage 并稍作修改，以便在连接多个摄像头的情况下，可以设置默认的一个。 -> 不工作

然后我尝试借助远程调试器在与我的机器具有相同 Windows 10 版本的其他 Windows 平板电脑上运行主应用程序（请记住，登录屏幕上的 BarcodeScanner 可以在我的机器上运行）。 -> 不工作

由于这些故障，我将运行代码从 main-apps LoginPage 复制到了一个全新的解决方案（我们称之为 test-app），其设置与原始解决方案相同。我什至尝试引用相同的 Dll，实现相同的设计模式等。 -> 不工作

我的机器： 赢 10 专业版 版本 1809 构建 17763.652

开发环境： 微软视觉工作室 2019 专业版 版本。 16.1.6

编辑：作为最低要求的 Windows 版本，我选择了 Build 16229 和 我的目标版本是 Build 17763（我的系统 Win 版本）

Widows 设置中的“允许应用访问您的相机”-选项被切换为开启，因此所有应用都可以访问相机。

Xaml

    <Page
        x:Class="QrCodeTest.MainPage"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="using:QrCodeTest"
        xmlns:vm="using:QrCodeTest.ViewModels"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        mc:Ignorable="d">

        <Page.DataContext>
            <vm:TestViewModel x:Name="ViewModel" />
        </Page.DataContext>

        <ScrollViewer>
            <StackPanel>
                <Button Content="Start Preview" HorizontalAlignment="Center" Click="Button_Click" Margin="5" />

                <CaptureElement x:Name="capturePreview" HorizontalAlignment="Center" Stretch="Uniform" Width="0" Height="0" Margin="10" />

                <Button Content="Stop Preview" HorizontalAlignment="Center" Click="Button_Click_1" Margin="5" />

                <TextBlock Text="{Binding Etikett, Mode=TwoWay}" HorizontalAlignment="Center" Margin="5" />
            </StackPanel>
        </ScrollViewer>
    </Page>

代码隐藏

private BarcodeScanner scanner { get; set; }
private ClaimedBarcodeScanner claimedScanner { get; set; }
private MediaCapture captureManager { get; set; }

internal async Task StartScannerAsync () {
            capturePreview.Visibility = Visibility.Visible;
            capturePreview.Width = 400; capturePreview.Height = 300;

            scanner = null;
            scanner = await DeviceHelpers.GetFirstDeviceAsync(BarcodeScanner.GetDeviceSelector(connectionTypes), async (id) => await BarcodeScanner.FromIdAsync(id));

            if (scanner != null) {
                captureManager = new MediaCapture();
                claimedScanner = await scanner.ClaimScannerAsync();

                if (claimedScanner != null) {
                    claimedScanner.ReleaseDeviceRequested += claimedScanner_ReleaseDeviceRequested;
                    claimedScanner.DataReceived += claimedScanner_DataReceived;

                    claimedScanner.IsDecodeDataEnabled = true;
                    IReadOnlyList<uint> supportedSymbologies = await scanner.GetSupportedSymbologiesAsync();

                    foreach (uint symbology in supportedSymbologies) {
                        listOfSymbologies.Add(new SymbologyListEntry(symbology));
                    }

                    await claimedScanner.EnableAsync();

                    MediaCaptureInitializationSettings _captureInitSettings = new MediaCaptureInitializationSettings {
                        VideoDeviceId = scanner.VideoDeviceId,
                        StreamingCaptureMode = StreamingCaptureMode.AudioAndVideo,
                        PhotoCaptureSource = PhotoCaptureSource.VideoPreview
                    };

                    await captureManager.InitializeAsync(_captureInitSettings);
                    capturePreview.Source = captureManager;

                    try {
                        // Change to false, in case you wanna compare different methods of doing the same
                        bool Like_MP_PAT_UWP = false;

                        if (Like_MP_PAT_UWP) {
                            await capturePreview.Source.StartPreviewAsync();
                            await claimedScanner.StartSoftwareTriggerAsync();
                        } else {


                            LocalDataContext.Etikett = "await captureManager.StartPreviewAsync();";
                            await captureManager.StartPreviewAsync();
                            await claimedScanner.StartSoftwareTriggerAsync();
                            Thread.Sleep(2000);
                            await claimedScanner.StopSoftwareTriggerAsync();
                            await captureManager.StopPreviewAsync();

                            LocalDataContext.Etikett = "await capturePreview.Source.StartPreviewAsync();";
                            await capturePreview.Source.StartPreviewAsync();
                            await claimedScanner.StartSoftwareTriggerAsync();
                            Thread.Sleep(2000);
                            await claimedScanner.StopSoftwareTriggerAsync();
                            await capturePreview.Source.StopPreviewAsync();

                            LocalDataContext.Etikett = "await claimedScanner.ShowVideoPreviewAsync();";
                            await claimedScanner.ShowVideoPreviewAsync();
                            await claimedScanner.StartSoftwareTriggerAsync();
                            Thread.Sleep(2000);
                            await claimedScanner.StopSoftwareTriggerAsync();
                            claimedScanner.HideVideoPreview();
                        }

                    } catch (Exception e) {
                        Exception x = e; displayRequest.RequestRelease();
                    } finally {
                        LocalDataContext.Etikett = string.Empty;
                    }

                }
            }
        }

视图模型：

public class TestViewModel: INotifyPropertyChanged {
        public static TestViewModel Instance { get; set; }

        private string _Etikett;
        public string Etikett { get { return _Etikett; } set { _Etikett = value; NotifyPropertyChanged(); } }

        public event PropertyChangedEventHandler PropertyChanged;
        public void NotifyPropertyChanged ([CallerMemberName] String propertyName = "") {
            //PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));

            if (PropertyChanged != null) {
                PropertyChanged.Invoke(this, new PropertyChangedEventArgs(propertyName));
            }
        }
}

我已经浪费了 4 个工作日来比较解决方案、代码等。上面的代码是从测试应用程序复制的，但它与主应用程序 LoginPage 上的代码基本相同（除了“如果(Like_MP_PAT_UWP) {...}"。

欢迎任何提示。

提前谢谢你。

Answer 1

问题在于 Kaspersky Endpoint Security 的“高级威胁防护/主机入侵防护”设置。它阻止了我们的开发硬盘驱动器（即我们的平板电脑或我们的网络驱动器）之外的所有应用程序访问相机（Dev-Drive = “Trusted Zone”）。

有必要在 Kaspersky Endpoint Security 中为整个环境重新配置该功能（将必要的位置/客户端声明为受信任区域）。

希望，这可能对遇到类似问题的人有所帮助，或者至少给某人一个提示。

Answer 2

只是在这里吐口水，但我建议尝试将您的测试减少为尽可能控制 MediaCapture 对象的代码，因为这似乎是您描述主要问题的症状。

之后，尝试将相机的共享模式降低为只读，以防其他应用程序正在使用具有独占访问权限的相机。此外，您可以将弹出同意检查减少到仅相机，而不是麦克风同意。有时，如果您在同意弹出窗口中不小心不同意，应用程序将被拒绝访问相机，直到您从系统设置（设置 -> 隐私 -> 相机）再次允许它。

以下是您上述内容的次优和精简版本，但包括所有部分。我试图将您开始条形码会话与处理物品分开。使用 MS 样品作为指导将比这个可靠得多。尽管如此，还有更多的跟踪点要添加，但下面有一些围绕 MediaCapture 失败的跟踪点，以及条形码扫描器启用部分中的其他点。希望对您有所帮助。

using System;
using System.Collections.Generic;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;

using Windows.Devices.PointOfService;
using System.Threading.Tasks;
using Windows.Media.Capture;
using Windows.Devices.Enumeration;
using System.Diagnostics;
using Windows.Storage.Streams;

namespace StackOverflowQrTest
{
    public sealed partial class MainPage : Page
    {
        public MainPage()
        {
            this.InitializeComponent();
        }
        private async void Button_Click(object sender, RoutedEventArgs e)
        {
            if (claimedScanner == null)
            { 
                await StartScannerAsync();
            }
        }
        private async void Button_Click_1(object sender, RoutedEventArgs e)
        {
            await StopScannerAsync();
        }

        private BarcodeScanner scanner { get; set; }
        private ClaimedBarcodeScanner claimedScanner { get; set; }
        private MediaCapture captureManager { get; set; }

        internal async Task StartScannerAsync()
        {
            capturePreview.Visibility = Visibility.Visible;
            capturePreview.Width = 400; capturePreview.Height = 300;

            scanner = await DeviceHelpers.GetFirstDeviceAsync(BarcodeScanner.GetDeviceSelector(), async (id) => await BarcodeScanner.FromIdAsync(id));

            if (scanner != null)
            {
                claimedScanner = await scanner.ClaimScannerAsync();
                if (claimedScanner != null)
                {
                    claimedScanner.ReleaseDeviceRequested += ClaimedScanner_ReleaseDeviceRequested;
                    claimedScanner.DataReceived += ClaimedScanner_DataReceived;
                    claimedScanner.IsDecodeDataEnabled = true;
                    await claimedScanner.EnableAsync();
                    try
                    {
                        bool haveAssociatedCamera = !string.IsNullOrEmpty(scanner.VideoDeviceId);
                        if (haveAssociatedCamera)
                        {
                            captureManager = new MediaCapture();
                            captureManager.Failed += CaptureManager_Failed;
                            MediaCaptureInitializationSettings _captureInitSettings = new MediaCaptureInitializationSettings
                            {
                                VideoDeviceId = scanner.VideoDeviceId,
                                SharingMode = MediaCaptureSharingMode.SharedReadOnly, // share
                                StreamingCaptureMode = StreamingCaptureMode.Video     // just video
                            };
                            await captureManager.InitializeAsync(_captureInitSettings);
                            capturePreview.Source = captureManager;
                        }

                        UpdateMessage("waiting..." + (!haveAssociatedCamera ? "But scanner not camera type" : ""));
                        if (captureManager != null) await captureManager.StartPreviewAsync();
                        await claimedScanner.StartSoftwareTriggerAsync();
                    }
                    catch (Exception e)
                    {
                        UpdateMessage(e.Message);
                        Debug.WriteLine("EXCEPTION: " + e.Message);
                    }
                }
                else
                {
                    UpdateMessage("Could not claim barcode scanner");
                }
            }
            else
            {
                UpdateMessage("No barcode scanners found");
            }

        }

        private void CaptureManager_Failed(MediaCapture sender, MediaCaptureFailedEventArgs errorEventArgs)
        {
            string msg = string.Format("MediaCapture_Failed: (0x{0:X}) {1}", errorEventArgs.Code, errorEventArgs.Message);
            UpdateMessage(msg);
        }

        internal async Task StopScannerAsync()
        {
            if (captureManager != null)
            {
                if (captureManager.CameraStreamState == Windows.Media.Devices.CameraStreamState.Streaming)
                {
                    await captureManager.StopPreviewAsync();
                }
                captureManager.Dispose();
                captureManager = null;
            }
            if (claimedScanner != null)
            {
                claimedScanner.Dispose();
                claimedScanner = null;
            }
            if (scanner != null)
            {
                scanner.Dispose();
                scanner = null;
            }
        }

        private void ClaimedScanner_DataReceived(ClaimedBarcodeScanner sender, BarcodeScannerDataReceivedEventArgs args)
        {
            var scanDataLabelReader = DataReader.FromBuffer(args.Report.ScanDataLabel);
            string barcode = scanDataLabelReader.ReadString(args.Report.ScanDataLabel.Length);

            UpdateMessage(barcode);
        }

        private void ClaimedScanner_ReleaseDeviceRequested(object sender, ClaimedBarcodeScanner e)
        {
            UpdateMessage("Another process is requesting barcode scanner device.");
            e.RetainDevice(); 
        }

        private async void UpdateMessage (string message)
        {
            await LastBarcodeRead.Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.Normal, () =>
            {
                LastBarcodeRead.Text = message;
            });
        }
    }

    public partial class DeviceHelpers
    {
        // We use a DeviceWatcher instead of DeviceInformation.FindAllAsync because
        // the DeviceWatcher will let us see the devices as they are discovered,
        // whereas FindAllAsync returns results only after discovery is complete.
        public static async Task<T> GetFirstDeviceAsync<T>(string selector, Func<string, Task<T>> convertAsync)
            where T : class
        {
            var completionSource = new TaskCompletionSource<T>();
            var pendingTasks = new List<Task>();
            DeviceWatcher watcher = DeviceInformation.CreateWatcher(selector);

            watcher.Added += (DeviceWatcher sender, DeviceInformation device) =>
            {
                Func<string, Task> lambda = async (id) =>
                {
                    T t = await convertAsync(id);
                    if (t != null)
                    {
                        completionSource.TrySetResult(t);
                    }
                };
                pendingTasks.Add(lambda(device.Id));
            };

            watcher.EnumerationCompleted += async (DeviceWatcher sender, object args) =>
            {
                // Wait for completion of all the tasks we created in our "Added" event handler.
                await Task.WhenAll(pendingTasks);
                // This sets the result to "null" if no task was able to produce a device.
                completionSource.TrySetResult(null);
            };

            watcher.Start();
            // Wait for enumeration to complete or for a device to be found.
            T result = await completionSource.Task;
            watcher.Stop();
            return result;
        }
    }
}

main xaml 在哪里...

<Page
    x:Class="StackOverflowQrTest.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:StackOverflowQrTest"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">

    <ScrollViewer>
        <StackPanel>
            <Button Content="Start Preview" HorizontalAlignment="Center" Click="Button_Click"  Margin="5" />
            <CaptureElement x:Name="capturePreview" HorizontalAlignment="Center" Stretch="Uniform" Width="0" Height="0" Margin="10" />
            <Button Content="Stop Preview" HorizontalAlignment="Center" Click="Button_Click_1"  Margin="5" />
            <TextBox Header="LastBarcode" Name="LastBarcodeRead" IsReadOnly="True" HorizontalAlignment="Center" Margin="5" />
        </StackPanel>
    </ScrollViewer>
</Page>