ViewModel屬性沒有更新時，它是相應的CustomControl屬性更新

Question

我想綁定視頻預覽自定義控件類中的IntPtr VidHandle屬性到它的視圖模型（vm：DebugHiResCameraWindowViewModel）中的IntPtr PreviewHandle。

在VideoPreview的構造，我呼籲：

this.VidHandle = picBox.Handle; 

更新VideoPreview的VidHandleProperty的DependencyProperty。這工作完美。但是，ViewModel中的PreviewHandle屬性未被更新。到時候我打電話：

camera.StartVideoStream(PreviewHandle); 

在視圖模型，PreviewHandle是0，因爲它從來沒有從VideoPreview更新。我有感覺我的DependencyProperty VidHandleProperty沒有正確實現，但我可能是錯的。

下面是一些代碼片段：

主窗口XAML：

<Window 
x:Class="AoiImageLift.Views.DebugHiResCameraWindow" 
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
xmlns:vm="clr-namespace:AoiImageLift.Presentation.ViewModels" 
xmlns:wf="clr-namespace:System.Windows.Forms;assembly=System.Windows.Forms" 
xmlns:com="clr-namespace:AoiImageLift.Components" 
xmlns:local="clr-namespace:AoiImageLift" 
Title="DebugHiResCameraWindow" 
Name="hiResWindow" 
Height="300" 
Width="300"> 
<Window.Resources> 
    <vm:DebugHiResCameraWindowViewModel x:Key="viewModel"/> 
</Window.Resources> 
<Grid> 
    <Grid.RowDefinitions> 
     <RowDefinition/> 
     <RowDefinition/> 
    </Grid.RowDefinitions> 

    <com:VideoPreview 
     DataContext="{StaticResource viewModel}" 
     x:Name="videoHost" 
     VidHandle="{Binding PreviewHandle, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type com:VideoPreview}}}"/> 

    <Button 
     DataContext="{StaticResource viewModel}" 
     Grid.Row="1" 
     Width="100" 
     Height="40" 
     Command="{Binding StartCaptureCommand}" 
     Content="Start"/> 
</Grid> 

VideoPreview類：

public class VideoPreview : WindowsFormsHost 
{ 
    private PictureBox picBox; 
    public static readonly DependencyProperty VidHandleProperty = 
     DependencyProperty.Register(
      "VidHandle", 
      typeof(IntPtr), 
      typeof(VideoPreview), 
      new FrameworkPropertyMetadata 
      { 
       BindsTwoWayByDefault = true 
      }); 

    public VideoPreview() : base() 
    { 
     picBox = new PictureBox(); 
     picBox.Width = (int) this.Width; 
     picBox.Height = (int) this.Height; 

     this.VidHandle = picBox.Handle; 
     this.Child = picBox; 
    } 

    public IntPtr VidHandle 
    { 
     get 
     { 
      return (IntPtr) GetValue(VideoPreview.VidHandleProperty); 
     } 
     set 
     { 
      SetValue(VideoPreview.VidHandleProperty, value); 
     } 
    } 
} 

視圖模型類：

public class DebugHiResCameraWindowViewModel : ViewModel 
{ 
    private Uri capturedImage; 
    private BitmapImage bmp; 
    private ISnapImages camera; 

    public DebugHiResCameraWindowViewModel() 
    { 
     camera = LumeneraCamera.Instance; 
     bmp = new BitmapImage(); 
    } 

    public IntPtr PreviewHandle { get; set; } 
    public Uri CapturedImage 
    { 
     get { return capturedImage; } 
     set { capturedImage = value; OnPropertyChanged("CapturedImage"); } 
    } 
    public ICommand StartCaptureCommand 
    { 
     get 
     { 
      return new DelegateCommand(() => 
      { 
       try 
       { 
        camera.StartVideoStream(PreviewHandle); 
       } 
       catch (CustomException ex) 
       { 
        MessageBox.Show(ex.Message, ex.Caption, ex.Button, ex.Image); 
       } 
      }); 
     } 
    } 
} 

Answer 1

看起來VideoPreview控件的VidHandle控件綁定到您的VideoPreview控件的PreviewHandle（它不存在）。

開始調試時檢查輸出窗口，它會顯示綁定錯誤（例如，當它找不到屬性時）。

也許這是你以後？

<Window 
x:Class="AoiImageLift.Views.DebugHiResCameraWindow" 
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
xmlns:vm="clr-namespace:AoiImageLift.Presentation.ViewModels" 
xmlns:wf="clr-namespace:System.Windows.Forms;assembly=System.Windows.Forms" 
xmlns:com="clr-namespace:AoiImageLift.Components" 
xmlns:local="clr-namespace:AoiImageLift" 
Title="DebugHiResCameraWindow" 
Name="hiResWindow" 
Height="300" 
Width="300"> 
<!-- CHANGED HERE: set DataContext of Window --> 
<Window.DataContext> 
    <vm:DebugHiResCameraWindowViewModel /> 
</Window.DataContext> 
<Grid> 
    <Grid.RowDefinitions> 
     <RowDefinition/> 
     <RowDefinition/> 
    </Grid.RowDefinitions> 

    <!-- CHANGED HERE: removed DataContext (set at Window) -- updated binding --> 
    <com:VideoPreview 
     x:Name="videoHost" 
     VidHandle="{Binding PreviewHandle}"/> 

    <!-- CHANGED HERE: removed DataContext (set at Window) -- binding OK --> 
    <Button 
     Grid.Row="1" 
     Width="100" 
     Height="40" 
     Command="{Binding StartCaptureCommand}" 
     Content="Start"/> 
</Grid> 

DataContext的是繼承，你可以在窗口中設置它，它會由子控件是已知的。

回覆：評論......虛擬機通常會優先 - 如果您在所有獲取/設置者上設置斷點，您可以看到該命令...... 0來自DP的默認值（可以是因爲DP是靜態的，所以它不能是PictureBox）。不知道這是適當的，但它的工作原理：

在你VideoPreview構造函數中添加：

base.Loaded += VideoPreview_Loaded; 

，並添加

void VideoPreview_Loaded(object sender, RoutedEventArgs e) 
{ 
    this.VidHandle = picBox.Handle; 
} 

在視圖中，更新綁定：

VidHandle="{Binding PreviewHandle, UpdateSourceTrigger=PropertyChanged}" 

您可能還想要Mode=OneWayToSource，假設手柄只能回來m VideoPreview