Question

   Using<GetFillupById>().Execute(id);

never saw such syntax.
definition of Using is:

protected T Using<T>() where T : class
    {
        var handler = serviceLocator.GetInstance<T>();
        if (handler == null)
        {
            throw new NullReferenceException("Unable to resolve type with service locator; type " + typeof(T).Name);
        }
        return handler;
    }

if someone can tell me what exactlythis thing is- function, property?
or show me some link where i can read about –
I will appreciate

Answer 1

This method/function uses a service locator to provide an instance of type T, returning that instance so it can be called. It’s analgous to this:

new GetFillupById().Execute(id);

but instead of a default constructor call, this helper method wraps up the object initialisation and delegates it to a service locator object. The use of generics allows this to be used as a single method call for any type recognised by the service locator.

The type constraint where T : class means that this method can be validly called for any type T which is a class rather than a structure, i.e. a reference rather than a value type. The converse would be where T : struct. You can also include constraints to say T must implement a particular interface, extend a certain class, or expose a default constructor (where T : new()).

Related concepts to look up: generics, inversion of control.