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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Extension methods in C#

Introduction

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.:

DateTime.Now.ToMyCustomDate();
string.ToThreeLetterAbbreviation();

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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Join custom objects into a concatenated string in .NET C#

Say you have the following Customer object with an overridden ToString method:

public class Customer
{
	public int Id { get; set; }
	public string Name { get; set; }
	public string City { get; set; }

	public override string ToString()
	{
		return string.Format("Id: {0}, name: {1}, city: {2}", Id, Name, City);
	}
}

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