附加属性和绑定
我正在创建一个附加行为，以便设置类的常规属性：
public class LookupHelper
{
public static readonly DependencyProperty ItemsSourceProperty = DependencyProperty.RegisterAttached("ItemsSource", typeof(object), typeof(LookupHelper), new UIPropertyMetadata(null, OnItemsSourceChanged));
private static void OnItemsSourceChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var control = d as MyControl;
if(control == null)
return;
control.ItemsSource = (IEnumerable)e.NewValue;
}
public static object GetItemsSource(GridColumn column)
{
return column.GetValue(ItemsSourceProperty);
}
public static void SetItemsSource(GridColumn column, object value)
{
column.SetValue(ItemsSourceProperty, value);
}
}
这里，MyControl 上的 ItemsSource 属性是常规属性，因此我无法在 Xaml 中绑定它，因此出现此附加行为。
现在，当我使用字符串或对象使用此附加属性时，它可以工作，并且会命中我设置的断点，但是当我使用绑定标记设置它时，它永远不会运行。为什么这不起作用？
<MyControl ctrl:LookupHelper.ItemsSource="DataSource"/>; //It works
<MyControl ctrl:LookupHelper.ItemsSource="{Binding Path=MyDataSource}"/>; //Does not work
我需要做的是将 ItemsSource 属性设置为 Binding 指定的值。
I'm creating an attached behavior in order to set a regular property of a class:
public class LookupHelper
{
public static readonly DependencyProperty ItemsSourceProperty = DependencyProperty.RegisterAttached("ItemsSource", typeof(object), typeof(LookupHelper), new UIPropertyMetadata(null, OnItemsSourceChanged));
private static void OnItemsSourceChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var control = d as MyControl;
if(control == null)
return;
control.ItemsSource = (IEnumerable)e.NewValue;
}
public static object GetItemsSource(GridColumn column)
{
return column.GetValue(ItemsSourceProperty);
}
public static void SetItemsSource(GridColumn column, object value)
{
column.SetValue(ItemsSourceProperty, value);
}
}
Here, ItemsSource property on MyControl is a regular property, so I can not bind it in Xaml, hence this attached behavior.
Now, when I use this attached property using string or objects it works and breakpoint I set is hit, but when I set it with Binding markup, it never runs. Why isn't this working?
<MyControl ctrl:LookupHelper.ItemsSource="DataSource"/>; //It works
<MyControl ctrl:LookupHelper.ItemsSource="{Binding Path=MyDataSource}"/>; //Does not work
What I need to do is to set the ItemsSource property to the value specified by the Binding.
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评论（2）
在 Get 和 Set 方法中，您将接收对象定义为 GridColumn，而它应该是 DependencyObject。
您可能还想将 DP 的类型从 object 更改为 IEnumerable ，因为您在更改处理程序中转换为该类型。
In your Get and Set methods, you're defining the receiving object as GridColumn where it should be DependencyObject.
You might also want to change the type of your DP from object to IEnumerable since your casting to that in your change handler.
您可以发布您正在使用的标记吗？另外，如果实际属性存在于对象上并且在那里有意义，那么我认为您应该在该对象上使用常规依赖属性，而不是辅助类上的附加属性。
编辑
来自 MSDN：
GetPropertyName 访问器的签名必须是：
SetPropertyName 访问器的签名必须是：
在您的情况下，GridColumn 是正确的目标类型吗？
Can you please post the markup you are using? Also, If the actual property exists on an object and makes sense there then I think you should be using a regular dependency property on that object instead of an attached property on a helper class.
Edit
From MSDN:
The signature for the GetPropertyName accessor must be:
and the signature for the SetPropertyName accessor must be:
In your case, is GridColumn the correct target type?