WPF附加属性触发两次

Question

我努力学习依赖属性和附加属性，所以请原谅我，如果你发现什么，我试图做没有用。

我有一个窗口，其DataContext设置到VM，并查看它是含有一个用户控件靶向这一VM一个DataTemplate通常MVVM方法。

我想使窗口容器尽可能愚蠢，因此我试图通过使用附加属性通过usercontrol定义通常驻留在窗口XAML（例如高度）的一些参数。

为了这个目的，我创建了下面的类，我定义的附加属性：

public static class WpfExtensions 
{ 
    public static readonly DependencyProperty ContainerHeightProperty = DependencyProperty.RegisterAttached(
     "ContainerHeight", 
     typeof(double), 
     typeof(WpfExtensions), 
     new FrameworkPropertyMetadata(300.0, FrameworkPropertyMetadataOptions.AffectsParentArrange | FrameworkPropertyMetadataOptions.AffectsParentMeasure | FrameworkPropertyMetadataOptions.AffectsRender, ContainerHeight) 
    ); 
    public static void SetContainerHeight(UIElement element, double value) 
    { 
     element.SetValue(ContainerHeightProperty, value); 
    } 
    public static double GetContainerHeight((UIElement element) 
    { 
     return (double)element.GetValue(ContainerHeightProperty); 
    } 

    private static void ContainerHeight(DependencyObject d, DependencyPropertyChangedEventArgs e) 
    { 
     if (d is UserControl) 
     { 
      UserControl l_Control = (UserControl)d; 

      Binding l_Binding = new Binding(); 

      l_Binding.RelativeSource = new RelativeSource(RelativeSourceMode.FindAncestor, typeof(Window), 1); 

      l_Binding.Path = new PropertyPath("Height"); 

      l_Binding.Mode = BindingMode.OneWayToSource; 

      BindingOperations.SetBinding(d, e.Property, l_Binding);   
     } 
    } 
} 

你可以看到，实现了容器窗口的高度，我在代码中创建从附加绑定的控制属性直至容器窗口。

然而ContainerHeight变化会被解雇的两倍。我第一次从300（默认）变为1024（在XAML中定义的）。然后我立即收到从1024回到300的另一个，我不明白为什么。

窗口代码非常简单：

<Window x:Class="WpfApplication.DialogWindow" 
     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
     xmlns:lcl="clr-namespace:WpfApplication" 
     Title="DialogWindow"> 
    <Window.Resources> 
     <DataTemplate DataType="{x:Type lcl:Dialog_VM}"> 
      <lcl:Dialog_VM_View /> 
     </DataTemplate> 
    </Window.Resources> 

    <ContentPresenter Content="{Binding }" /> 

</Window> 

最后简单的视图模型

<UserControl x:Class="WpfApplication.Dialog_VM_View" 
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
    xmlns:lcl="clr-namespace:WpfApplication" 
    mc:Ignorable="d" 
    d:DesignHeight="300" d:DesignWidth="300" 
    lcl:WpfExtensions.ContainerHeight="1024"> 

    <StackPanel> 
     <TextBlock Text="This is a test" /> 
    </StackPanel> 

</UserControl> 

Answer 1

你应该父窗口的Height属性绑定的附加属性，而不是周围的其他方法，不是吗？

这套（绑定）的父窗口的Height到1024这是依赖属性在UserControl值：

private static void ContainerHeight(DependencyObject d, DependencyPropertyChangedEventArgs e) 
{ 
    if (d is UserControl) 
    { 
     UserControl l_Control = (UserControl)d; 
     if (!l_Control.IsLoaded) 
     { 
      l_Control.Loaded += L_Control_Loaded; 
     } 
     else 
     { 
      Bind(l_Control); 
     } 
    } 
} 

private static void L_Control_Loaded(object sender, RoutedEventArgs e) 
{ 
    UserControl l_Control = (UserControl)sender; 
    Bind(l_Control); 
} 

private static void Bind(UserControl l_Control) 
{ 
    Window window = Window.GetWindow(l_Control); 

    Binding l_Binding = new Binding(); 
    l_Binding.Path = new PropertyPath(WpfExtensions.ContainerHeightProperty); 
    l_Binding.Source = l_Control; 

    BindingOperations.SetBinding(window, Window.HeightProperty, l_Binding); 
}