在WPF中使用附加的属性

Question

我想在WPF中创建一个只读附加属性，它将计算控件的总可视子项数。这对我来说并不重要，它可以正确使用附加属性！

首先我声明我的财产，像这样：

internal static readonly DependencyPropertyKey TotalChildCountPropertyKey = 
     DependencyProperty.RegisterAttachedReadOnly("TotalChildCount", typeof(int), typeof(MyAttachClass), new FrameworkPropertyMetadata(0)); 

    public static readonly DependencyProperty TotalChildCountProperty = TotalChildCountPropertyKey.DependencyProperty; 


    public static int GetTotalChildCount(DependencyObject obj) 
    { 
     return (int)obj.GetValue(TotalChildCountProperty); 
    } 

    public static void SetTotalChildCount(DependencyObject obj, int value) 
    { 
     obj.SetValue(TotalChildCountPropertyKey, value); 
    } 

我也有一个递归方法声明别的地方，像这样：

public static class Recursive 
{ 
    public static IEnumerable<DependencyObject> GetAllChildren(DependencyObject obj) 
    { 
     List<DependencyObject> col = new List<DependencyObject>(); 
     GetAllChildrenImp(obj, col); 
     return col; 

    } 

    private static void GetAllChildrenImp(DependencyObject current,  List<DependencyObject> col) 
    { 
     if (current != null) 
     { 
      col.Add(current); 

      for (int i = 0; i < VisualTreeHelper.GetChildrenCount(current); i++) 
      { 
       GetAllChildrenImp(VisualTreeHelper.GetChild(current, i), col); 
      } 
     } 
    } 
} 

现在我想用这种方法来分配值给GetTotalChildCount属性，但我找不出最好的方法。我可以将一个事件处理程序添加到依赖项属性更改中，但是这绝不会触发，因为我只能从xaml中读取值。

这里是我如何在XAML中使用它：

<TextBox DataContext="{RelativeSource Self}" Text="{Binding local:MyAttachClass.TotalChildCount}"></TextBox> 

所以来概括。我希望设置一个DependencyObjects TotalChildCount附加属性，然后能够在xaml中绑定它。就目前而言，这不起作用，GetTotalChildCount甚至没有被击中。

哦，这是我的第一个问题，希望我很清楚

Answer 1

，您可以尝试这样

附加属性

public class MyAttachClass 
{ 
    public static readonly DependencyProperty TotalChildCountProperty = DependencyProperty.RegisterAttached("TotalChildCount", typeof(int), typeof(MyAttachClass), 
    new PropertyMetadata(-1, OnTotalChildCountChanged)); 

    public static int GetTotalChildCount(DependencyObject obj) 
    { 
     return (int)obj.GetValue(TotalChildCountProperty); 
    } 

    public static void SetTotalChildCount(DependencyObject obj, int value) 
    { 
     obj.SetValue(TotalChildCountProperty, value); 
    } 

    public static void OnTotalChildCountChanged(object sender, DependencyPropertyChangedEventArgs e) 
    { 
     TextBox txt = sender as TextBox; 
     if (txt != null) 
     { 
      var children = Recursive.GetAllChildren(txt); 
      txt.Text = children.Count().ToString(); 
     } 
    } 
} 

而XAML为

<TextBox local:MyAttachClass.TotalChildCount="0" ></TextBox> 

希望能帮助到你！