Prism / Unity：无法导航到弹出区域

Question

我有一个Prism 6.3 / Unity WPF应用程序，该应用程序将在启动后查找已安装的扫描仪，如果没有，则向用户显示一条消息。为了呈现此消息，我的Shell视图中有一个通常折叠的特殊区域：

Shell.xaml

    <Grid Grid.ColumnSpan="3" Grid.RowSpan="3" Panel.ZIndex="2" Visibility="{Binding MessageVisibility}" 
          fade:VisibilityAnimation.AnimationType="Fade">
        <Grid.RowDefinitions>
            <RowDefinition Height="15*"/>
            <RowDefinition Height="70*"/>
            <RowDefinition Height="15*"/>
        </Grid.RowDefinitions>

        <Rectangle Grid.Row="0" Fill="{DynamicResource AccentColorBrush2}"/>
        <ContentControl Grid.Row="1" prism:RegionManager.RegionName="{x:Static local:RegionNames.PopUpRegionName}"/>
        <Rectangle Grid.Row="2" Fill="{DynamicResource AccentColorBrush2}"/>
    </Grid>

创建消息后，事件聚合器会触发这样的事件

_eventAggregator.GetEvent<ShowMessage>().Publish(message);

和ShellViewModel像这样监听此事件：

ShellViewModel构造函数和方法

_eventAggregator.GetEvent<ShowMessage>().Subscribe(ReceiveMessage);

public void ReceiveMessage(Models.Message message)
{
    _regionManager.RequestNavigate(RegionNames.PopUpRegionName, "MessageView");
    MessageVisibility = Visibility.Visible;
}

之后，将弹出消息区域，并向用户显示消息。

Bootstrapper：

public class Bootstrapper : UnityBootstrapper
{
    public override void Run(bool runWithDefaultConfiguration)
    {
        base.Run(runWithDefaultConfiguration);

        (Container.Resolve(typeof(ScanViewModel)) as ScanViewModel).InitializeTwain();
    }

    protected override System.Windows.DependencyObject CreateShell()
    {
        return Container.Resolve(typeof(Shell), "Shell") as DependencyObject;
    }

    protected override void InitializeShell()
    {
        base.InitializeShell();
        var mainWindow = (Shell)this.Shell;
        Application.Current.MainWindow = mainWindow;                       
        mainWindow.Show();
    }

    protected override void ConfigureServiceLocator()
    {
        base.ConfigureServiceLocator();
        Container.RegisterType<IEventAggregator, EventAggregator>(new ContainerControlledLifetimeManager());
        Container.RegisterType<IMessageViewModel, MessageViewModel>(new ContainerControlledLifetimeManager());
        Container.RegisterType<IFolderSelectionViewModel, FolderSelectionViewModel>(new ContainerControlledLifetimeManager());
        Container.RegisterType<IRegionManager, RegionManager>(new ContainerControlledLifetimeManager());

        var regionManager = Container.TryResolve<IRegionManager>();
        regionManager.RegisterViewWithRegion(RegionNames.PopUpRegionName, typeof(Views.MessageView));
        regionManager.RegisterViewWithRegion(RegionNames.PopUpRegionName, typeof(Views.FolderSelectionView));
    }
}

ScanViewModel InitializeTwain（）方法

public void InitializeTwain()
{
        try
        {
            twain = new Twain(new WpfWindowMessageHook(Application.Current.MainWindow));
            SelectedScanner = null;
            Scanners = new ObservableCollection<string>();
            for (int i = 0; i < twain.SourceNames.Count; i++)
            {
                Scanners.Add(twain.SourceNames[i]);
            }

            if (Scanners.Count > 0)
                SelectedScanner = Scanners[0];
            else
                throw new TwainException();

            twain.ScanningComplete += Twain_ScanningComplete;

            twain.TransferImage += delegate (object sender, TransferImageEventArgs args)
            {
                if (args.Image != null)
                {
                    resultImage = args.Image;
                    images.Add(resultImage);
                }
            };
            canScan = true;
            ((DelegateCommand)ScanCommand).RaiseCanExecuteChanged();
        }
        catch (TwainException)
        {
            canScan = false;
            ((DelegateCommand)ScanCommand).RaiseCanExecuteChanged();
            Message = new Models.Message("TwainException", "No TWAIN compatible scanner could be found.");
            // _eventAggregator.GetEvent<ShowMessage>().Publish(message) gets called here
        }
    }

我的问题：

当我在引导程序的Run（）方法中调用InitializeTwain（）方法，并且应该向用户显示不存在扫描仪的消息时，不会显示PopupRegion，而是底层的ScanView。而且我无法在ScanView中单击任何内容，因此某些内容将其隐藏。

当我从引导程序的Run（）方法中删除InitializeTwain（）调用并创建一个调用它的按钮，并在应用程序加载后单击它时，该消息将正确显示。

我想念什么？

Answer 1

[尝试等待调用该方法，直到外壳窗口已加载，即不要覆盖Run，而是为Loaded中的InitializeShell事件挂接事件处理程序：

protected override void InitializeShell()
{
    base.InitializeShell();
    var mainWindow = (Shell)this.Shell;
    Application.Current.MainWindow = mainWindow;
    mainWindow.Loaded += OnLoaded;
    mainWindow.Show();
}

private void OnLoaded(object sender, RoutedEventArgs e)
{
    var window = (Window)sender;
    window.Loaded -= OnLoaded;

    (Container.Resolve(typeof(ScanViewModel)) as ScanViewModel).InitializeTwain();
}