wpf - 带有绑定(bind)参数的 MarkupExtension

Question

我正在定制 MarkupExtension其中我需要来自 XAML 的非字符串参数来构造新对象。是否可以在 DataContext 中的字段上使用非字符串参数绑定(bind)？范围？

换句话说，我怎么能做这样的事情？

<ListBox ItemsSource="{Binding Source={local:MyMarkupExtension {x:Type Button},IncludeMethods={Binding Source=CustomerObject.IsProblematic}}}" />

在哪里 IncludeMethods=CustomerObject.IsProblematic给我这个错误:

Binding cannot be set on the 'IncludeMethods' property of type 'TypeDescriptorExtension'. A 'Binding' can only be set on a DependencyProperty of a DependencyObject.

谁能帮我？

谢谢

Answer 1

我找到了解决这个问题的方法。
主要思想是为每个需要绑定(bind)的参数定义附加属性。

public class MarkupExtensionWithBindableParam : MarkupExtension
{
    public BindingBase Param1 { get; set; } // its necessary to set parameter type as BindingBase to avoid exception that binding can't be used with non DependencyProperty

    public override object ProvideValue(IServiceProvider serviceProvider)
    {
        IProvideValueTarget target = serviceProvider.GetService(typeof(IProvideValueTarget)) as IProvideValueTarget;
        DependencyObject targetObject;
        DependencyProperty targetProperty;
        
        if (target != null && target.TargetObject is DependencyObject && target.TargetProperty is DependencyProperty)
        {
            targetObject = (DependencyObject)target.TargetObject;
            targetProperty = (DependencyProperty)target.TargetProperty;
        }
        else
        {
            return this; // magic
        }

        // Bind the Param1 to attached property Param1BindingSinkProperty 
        BindingOperations.SetBinding(targetObject, MarkupExtensionWithBindableParam.Param1BindingSinkProperty, Param1);

        // Now you can use Param1
        
        // Param1 direct access example:
        object param1Value = targetObject.GetValue(Param1BindingSinkProperty);
        
        // Param1 use in binding example:
        var param1InnerBinding = new Binding() { Source = targetObject, Path = new PropertyPath("(0).SomeInnerProperty", Param1BindingSinkProperty) }); // binding to Param1.SomeInnerProperty
        return param1InnerBinding.ProvideValue(serviceProvider); // return binding to Param1.SomeInnerProperty
    }

    private static DependencyProperty Param1BindingSinkProperty = DependencyProperty.RegisterAttached("Param1BindingSink", typeof(object)// set the desired type of Param1 for at least runtime type safety check
                       , typeof(MarkupExtensionWithBindableParam ), new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.Inherits));
}

用法很简单:

<TextBlock Text="{local:MarkupExtensionWithBindableParam Param1={Binding Path='SomePathToParam1'}}"/>