Saturday, October 18, 2008

Extension Methods in C#

There are some new features in C# 3 which are introduced to make LINQ possible.
One of them are extension methods which I wanted to try out. Extension methods are static methods which can be applied to any object type which is specified as "special parameter". For example if you want to extend the type string with the method "Greet" you write something like this:
public static void Greet(this String s)
Console.WriteLine("Hello " + s);

Then you can call it like:
string name = "Tom";

This will produce the following on the console: "Hello Tom"

I played a bit with this extension mehtods and came up with the following extensions for object which I believe can be helpful.
Assume the following object:
Customer testCustomer = new Customer() { Name = "John", Age = 35, LastName = "Smith" };

PrintConsole() -> prints the string representation of an object to the console


PrintMessageBox() -> shows the string representation of an object in a message box


PrintPropertiesConsole() -> Prints all public non inherited properties and their values of the object to the console

Properties of 'ExtensionMethodTest.Customer'
Name: John
LastName: Smith
Age: 35

PrintPropertiesMessageBox() -> Shows all public non inherited properties and their values of the object in a message box


string ToXml() -> Serializes the object to XML and returns the XML string



ToXml(Stream stream) -> Serializes the object to XML and writes it to the stream

ToXml(string fileName) -> Serializes the object to XML and writes the XML string to the file specified.

If you are interested in my project you can download it from here.
Or you can simply download the Extensions.dll from here and import it into your project.

All extension methods are in the namespace System. I know that this is not the way how to do it but so you don't have to add a using directive because System is by default present.


For them of you which do not know what XPath is; it is a very powerful query language for XML data. But it can also more than querying data; it can also compute values, find the max or min of an attribute and even produce a different output format. For example it is possible to write HTML code with XML data. C# provides different classes to execute XPath queries on XML files which are located in the "System.Xml.Xpath" namespace.
The problem, at least for me, is that I do not use XPath so often as that I always remember the sometimes tricky XPath-Syntax. Here I found it very helpful to have a graphical tool where I can type in my query and see the results of the query. I found such a tool which is freeware; Sketch Path. It is a very powerful tool which not only shows you the result of a query but also assists you when writing a query by providing common operations and selectors.

I can only encourage you to try XPath when working with XML data because it really makes it easier to get the data you want. Especially if you use XML files instead of a database. XPath can be seen as the SQL for XML files.

Here there is a screenshot of Sketch Path where I searched in a list of customers for all customers which are older than 50. The query is quite simple:

Another nice thing which is very helpful is that if you select a node then it shows you the path to this node which can help you creating your query:

Here you can find a tutorial on XPath Syntax.