How to Create Custom MarkupExtension like StaticResource?

Question

please help me how to create a MarkupExtension looks like StaticResource of wpf, i have:

my own class:

public class Item{

public string Value{get; set;}
public string Title{get;set;}
}

and in a Resource Dictionary i have:

// ...
<gpf:Item x:Key="firstone" Value="Hi" Title="Welcome"/> 
//...

i want to use my Item looks like:

// ...
<TextBlock Text="{MyEX firstone}"/>
//...

i tired to do this but i do not know how to finish my work:

    //...
    [Localizability(LocalizationCategory.NeverLocalize)]
    [MarkupExtensionReturnType(typeof(string))]
    public class MyEX : MarkupExtension
    {
        public MyEX () { 
        }

        public override object ProvideValue(IServiceProvider serviceProvider)
        {
            return ??? ;
        }
    }

Answer 1

You could take the resource key into your custom markup extension as a parameter via Constructor.

You could then, in your ProvideValue method, create a StaticResourceExtension and get the actual resource (in your case an instance of Item) by calling ProvideValue method.

Quick Implementation

[MarkupExtensionReturnType(typeof(string))]
public class MyExtension : MarkupExtension
{
    public MyExtension(string resourceKey)
    {
        ResourceKey = resourceKey;
    }

    string ResourceKey { get; set; }

    public override object ProvideValue(IServiceProvider serviceProvider)
    {
        var staticResourceExtension = new StaticResourceExtension(ResourceKey);
        
        var resource = staticResourceExtension.ProvideValue(serviceProvider) as Item;
        
        return resource == null ? "Invalid Item" : String.Format("My {0} {1}", resource.Value, resource.Title);
    }
}

You may have to add more code in ProvideValue to handle design mode, etc.