Method-Chaining in C#

The technique you mention is called chainable methods. It is commonly used when creating DSLs or fluent interfaces in C#.

The typical pattern is to have your AddItem() method return an instance of the class (or interface) it is part of. This allows subsequent calls to be chained to it.

public MyCollection AddItem( MyItem item )
{
   // internal logic...

   return this;
}

Some alternatives to method chaining, for adding items to a collection, include:

Using the params syntax to allow multiple items to be passed to your method as an array. Useful when you want to hide the array creation and provide a variable argument syntax to your methods:

public void AddItems( params MyItem[] items )
{
    foreach( var item in items )
        m_innerCollection.Add( item );
}

// can be called with any number of arguments...
coll.AddItems( first, second, third );
coll.AddItems( first, second, third, fourth, fifth );

Providing an overload of type IEnumerable or IEnumerable so that multiple items can be passed together to your collection class.

public void AddItems( IEnumerable<MyClass> items )
{
    foreach( var item in items )
         m_innerCollection.Add( item );
}

Use .NET 3.5 collection initializer syntax. You class must provide a single parameter Add( item ) method, implement IEnumerable, and must have a default constructor (or you must call a specific constructor in the initialization statement). Then you can write:

var myColl = new MyCollection { first, second, third, ... };