Question

Example:

For reasons outside the scope of this example, I am forced to use this:

UserRepository repository = new UserRepository();
User user = (User)InvokeMethod(repository, "GetUserById", new object[]{2});

private object InvokeMethod(object source, string methodName, object[] parameters)
{
    Type sourceType = source.GetType();
    MethodInfo methodInfo = sourceType.GetMethod(methodName);
    return methodInfo.Invoke(source, parameters);            
}

However, I would much prefer something like this:

UserRepository repository = new UserRepository();
User user = GetUserById<User, UserRepository>(repository, m => m.GetUserById(2));

A wrapper could accomplish this. I started to build one, but got stuck. This is what I have:

public TUser GetUserById<TUser, TUserRepository>(TUserRepository repository, Expression<Func<TUserRepository, TUser>> repositoryFunc)
     where TUser : User
     where TUserRepoistory : UserRepository
{
    // How do I use the Expression to setup the next two statements?
    string methodName = ""; // should be "GetUserId"
    object[] params = null; // should be "object[] { 2 }"

    TUser user = (TUser)InvokeMethod(repository, methodName, parameters);
}

Keep in mind I am forced to use the InvokeMethod method. I cannot simply invoke the Func.

Answer 1

This gets complex depending on whether the arguments are literals, captured variables, etc – and whether they are ref, out, etc. You might want to look at the implementation in protobuf-net.Extensions, here, which has code to all of this – in particular the ResolveMethod method.

The MethodInfo is simple – just cast Body to MethodCallExpression and obtain the .Method.Name – but for the parameters it recursively calls into Evaluate – this allows expressions like SomeMethod(123, x, y.Foo.Bar) to work, where 123 is a literal, x is a captured variable, and y.Foo.Bar is something hanging off a captured variable.