How to store a generic function in a variable in c#? [duplicate]

Question

I have the following code:

public interface IMenuItem
{
    IWebElement Parent { get; }
}

public class MenuItems
{
    public T GetMenuItem<T>() where T : IMenuItem, new()
    {
        var menuItem = new T();

        return menuItem;
    }
}

public abstract class Page : IEnumerable<IComponent>
{
    private Func<IMenuItem> _getMenuItems = new MenuItems().GetMenuItem<IMenuItem>;
}

I'm trying to store the new MenuItems().GetMenuItem<IMenuItem> function in _getMenuItems field, but since this is a generic function this isn't working. How can I store generic functions into a variable?

Doing new MenuItems().GetMenuItem<IMenuItem> won't work and it tells me:

'IMenuItem' must be a non-abstract type with a public parameterless constructor in order to use it as parameter 'T' in the generic type or method 'MenuItems.GetMenuItem()'

Now I have many concrete types that implement IMenuItem I want the delegate to accept those. I don't want to make a seperate delegate for every concrete type that implements IMenuItem. Rather I have a single delegate that can accept concrete types that implement IMenuItem.

Answer 1

The problem is with the new() constraint.

The new constraint specifies that a type argument in a generic class declaration must have a public parameterless constructor. To use the new constraint, the type cannot be abstract.

Since IMenuItem is an interface, it cannot be instantiated, and therefore the new() constraint will be a problem.

Edit:

You can solve this in a couple of ways:

1. You can use reflection for retrieving the method and invoking it:

   var method = typeof(MenuItems).GetMethod("GetMenuItem");
   var instance = new MenuItems(); // Maybe convert the class into a static class??
   var genericMethod = method.MakeGenericMethod(typeof(MenuItem1));
   var result = genericMethod.Invoke(instance, null) as IMenuItem;
   

2. Use dynamic to invoke it:

   dynamic instance = new MenuItems(); // Maybe convert the class into a static class??
   var result = instance.GetMenuItem<MenuItem1>() as IMenuItem;
   

3. Hold an instance of MenuItems instead of the method itself:

   var menuItems = new MenuItems();
   var result = _instance.GetMenuItem<MenuItem1>() as IMenuItem;