c# - ViewModel 属性在其对应的 CustomControl 属性更新时未更新

Question

我正在尝试将 VideoPreview 自定义控件类中的 IntPtr VidHandle 属性绑定(bind)到其 View 模型 (vm:DebugHiResCameraWindowViewModel) 中的 IntPtr PreviewHandle。

在 VideoPreview 的构造函数中，我调用:

this.VidHandle = picBox.Handle;

更新 VideoPreview 的 VidHandleProperty DependencyProperty。这完美地工作。但是，ViewModel 中的 PreviewHandle 属性并未更新。当我打电话时:

camera.StartVideoStream(PreviewHandle);

在 View 模型中，PreviewHandle 为 0，因为它从未从 VideoPreview 更新。我感觉我的 DependencyProperty VidHandleProperty 没有正确实现，但我可能是错的。

以下是一些代码片段:

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>

视频预览类:

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);
        }
    }
}

查看模型类:

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

看起来像 VidHandle的VideoPreview控件绑定(bind)到 PreviewHandle您的VideoPreview控制(不存在)。

开始调试时检查输出窗口，它应该会显示绑定(bind)错误(例如，当它找不到属性时)。

也许这就是你所追求的？

<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 是继承的，你可以在 Window 设置它，它会被子控件知道。

回复:评论... VM 通常优先 - 如果您在所有 getter/setter 上设置断点，您可以看到顺序... 0 来自 DP 的默认值(可以在元数据中设置) ，但它不能属于 PictureBox，因为 DP 是静态的)。不确定这是否合适，但它有效:

在您的 VideoPreview构造函数，添加:

base.Loaded += VideoPreview_Loaded;

并添加

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

在 View 中，更新绑定(bind):

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

您可能还想要 Mode=OneWayToSource , 假设句柄应该只来自 VideoPreview