c# - How do I create a delegate for a .NET property?

Question

I am trying to create a delegate (as a test) for:

Public Overridable ReadOnly Property PropertyName() As String

My intuitive attempt was declaring the delegate like this:

Public Delegate Function Test() As String

And instantiating like this:

Dim t As Test = AddressOf e.PropertyName

But this throws the error:

Method 'Public Overridable ReadOnly Property PropertyName() As String' does not have a signature compatible with delegate 'Delegate Function Test() As String'.

So because I was dealing with a property I tried this:

Public Delegate Property Test() As String

But this throws a compiler error.

So the question is, how do I make a delegate for a property?

---

See this link:

http://peisker.net/dotnet/propertydelegates.htm

Answer 1

Re the problem using AddressOf - if you know the prop-name at compile time, you can (in C#, at least) use an anon-method / lambda:

Test t = delegate { return e.PropertyName; }; // C# 2.0
Test t = () => e.PropertyName; // C# 3.0

I'm not a VB expert, but reflector claims this is the same as:

Dim t As Test = Function 
    Return e.PropertyName
End Function

Does that work?

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Original answer:

You create delegates for properties with Delegate.CreateDelegate; this can be open for any instance of the type, of fixed for a single instance - and can be for getter or setter; I'll give an example in C#...

using System;
using System.Reflection;
class Foo
{
    public string Bar { get; set; }
}
class Program
{
    static void Main()
    {
        PropertyInfo prop = typeof(Foo).GetProperty("Bar");
        Foo foo = new Foo();

        // create an open "getter" delegate
        Func<Foo, string> getForAnyFoo = (Func<Foo, string>)
            Delegate.CreateDelegate(typeof(Func<Foo, string>), null,
                prop.GetGetMethod());

        Func<string> getForFixedFoo = (Func<string>)
            Delegate.CreateDelegate(typeof(Func<string>), foo,
                prop.GetGetMethod());

        Action<Foo,string> setForAnyFoo = (Action<Foo,string>)
            Delegate.CreateDelegate(typeof(Action<Foo, string>), null,
                prop.GetSetMethod());

        Action<string> setForFixedFoo = (Action<string>)
            Delegate.CreateDelegate(typeof(Action<string>), foo,
                prop.GetSetMethod());

        setForAnyFoo(foo, "abc");
        Console.WriteLine(getForAnyFoo(foo));
        setForFixedFoo("def");
        Console.WriteLine(getForFixedFoo());
    }
}