How do I invoke an extension method using reflection?

user_31188 0
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I appreciate that similar questions have been asked before, but I am struggling to invoke the Linq Where method in the following code. I am looking to use reflection to dynamically call this method and also dynamically build the delegate (or lambda) used in the Where clause. This is a short code sample that, once working, will help to form part of an interpreted DSL that I am building. Cheers.

    public static void CallWhereMethod()
    {
        List<MyObject> myObjects = new List<MyObject>(){new MyObject{Name="Jon Simpson"}};
        System.Delegate NameEquals = BuildEqFuncFor<MyObject>("Name", "Jon Simpson");
        object[] atts = new object[1] ;
        atts[0] = NameEquals;

        var ret = typeof(List<MyObject>).InvokeMember("Where", BindingFlags.InvokeMethod, null, InstanceList,atts);
    }

    public static Func<T, bool> BuildEqFuncFor<T>(string prop, object val)
    {
        return t => t.GetType().InvokeMember(prop,BindingFlags.GetProperty,
                                             null,t,null) == val;
    }
delegates reflection lambda linq c#
6 Answers

Here's an answer for a general case where the method name is unique (so not the same case the original question posed, because Enumerable.Where is overloaded).

Say you have a target object targetObject of the type which is extended, where the extension method is defined in a class TargetClassExtensions and whose extension method's name is ExtensionMethod which takes in an integer parameter and is generic for which you want to call for the class TargetGenericClass.

Then, to call this extension method through reflection, do the following:

int inputInteger = 9; // Example input for the generic method.

object? result = typeof(TargetClassExtensions)
    .GetMethod(nameof(TargetClassExtensions.ExtensionMethod))
    .MakeGenericMethod(typeof(TargetGenericClass))
    .Invoke(null, new object[] { targetObject, inputInteger });
user_12503190
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