Implementing an enumerator for a custom object in .NET C#

You can create an enumerator for a custom type by implementing the generic IEnumerable of T interface. Normally you’d do that if you want to create a custom collection that others will be able to iterate over using foreach. However, there’s nothing stopping you from adding an enumerator to any custom type if you feel like it, it’s really simple.

Consider the following Guest class:

public class Guest
	public string Name { get; set; }
	public int Age { get; set; }

Guests can be invited to a Party:

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Keeping the key-values sorted by using a SortedDictionary with C# .NET

You can use the generic SortedDictionary of Key and Value to automatically keep the key value items sorted by their keys. Any time you add a new key value pair the dictionary will reorder the items. The SortedDictionary was optimised for frequent changes to its list of items. Keep in mind that the items will be sorted by their key and not their value.

Consider the following simple custom object:

public class Student
	public string Name { get; set; }
	public string SchoolName { get; set; }

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Using the KeyedCollection object in C# .NET

The abstract generic KeyedCollection object can be used to declare which field of your custom object to use as a key in a Dictionary. It provides sort of a short-cut where you’d want to organise your objects in a Dictionary by an attribute of that object.

Let’s take the following object as an example:

public class CloudServer
	public string CloudProvider { get; set; }
	public string ImageId { get; set; }
	public string Size { get; set; }

The Image IDs are always unique so the ImageId property seems to be a good candidate for a dictionary key.

Here’s an example:

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Getting notified when collection changes with ObservableCollection in C# .NET

Imagine that you’d like to be notified when something is changed in a collection, e.g. an item is added or removed. One possible solution is to use the built-in .NET generic collection type ObservableCollection of T which is located in the System.Collections.ObjectModel namespace. The ObservableCollection object has an event called CollectionChanged. You can hook up an event handler to be notified of the changes.

If you don’t know what events, event handlers and delegates mean then start here.

Let’s see a simple example with a collection of strings:

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Customise your list by overriding Collection of T with C# .NET

Imagine that you’d like to build a list type of collection where you want to restrict the insertion and/or deletion of items in some way. Let’s say we need an integer list with the following rules:

  • The allowed range of integers is between 0 and 10 inclusive
  • A user should not be able to remove an item at index 0
  • A user should not be able to remove all items at once

One possible solution is to derive from the Collection of T class. The generic Collection of T class in the System.Collections.ObjectModel namespace provides virtual methods that you can override in your custom collection.

The virtual InsertItem and SetItem methods are necessary to control the behaviour of the Collection.Add and the way items can be modified through an indexer:

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Extension methods in C#


Extension methods in C# allow you to extend the functionality of types that you didn’t write and don’t have direct access to. They look like integral parts of any built-in classes in .NET, e.g.:


You can extend the following types in C#:

  • Classes
  • Structs
  • Interfaces

You can extend public types of 3rd party libraries. You can also extend generic types, such as List of T and IEnumerable of T. You cannot extend sealed classes.

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Extending class definitions with partial classes in C# .NET

The ‘partial’ keyword helps you divide your classes into multiple files within the same namespace. One obvious usage of partial classes is to split the definition of a large type into smaller chunks. You cannot just use the partial keyword with classes but methods as well.

The partial classes will reside in two – or more – different cs files in the same namespace. Say you have a partial Customer class in the project-name/domains folder:

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