C# 3.0 and .Net Framework 3.5 in introduce several new features. One of them is extension methods. Extension methods enable you to “add” new methods to the existing types. Extension methods are a special kind of static methods, but they are called as same as the instance methods. In this blog I will show you how to extend SharePoint API by using extension methods.
Here are my extension methods for “SPList” object.
using System;
using Microsoft.SharePoint;
namespace ConsoleApplication1.ExtensionMethods
{
// Extension methods must be defined in a static class.
public static class SPListExtension
{
// This is the extension method.
// The first parameter takes the "this" modifier.
public static string GetFullUrl(this SPList list)
{
return string.Format("{0}/{1}", list.ParentWeb.Url, list.RootFolder.Url);
}
public static bool HasView(this SPList list, string viewName)
{
if (string.IsNullOrEmpty(viewName))
{
return false;
}
foreach (SPView view in list.Views)
{
if (view.Title.Equals(viewName, StringComparison.InvariantCultureIgnoreCase))
{
return true;
}
}
return false;
}
}
}
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Application with the extension methods
using System;
using ConsoleApplication1.ExtensionMethods;
using Microsoft.SharePoint;
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
using (SPSite site = new SPSite("http://localhost"))
{
using (SPWeb web = site.OpenWeb())
{
SPList list = web.Lists["Tasks"];
Console.WriteLine(string.Format("The full url of Tasks is: {0}", list.GetFullUrl()));// Call an extension mothod.
Console.WriteLine();
string viewName = "My Tasks";
Console.WriteLine("View Name: My Tasks");
Console.WriteLine(list.HasView(viewName)); // Call an extension mothod.
Console.WriteLine();
viewName = "abc 123";
Console.WriteLine("View Name: abc 123");
Console.WriteLine(SPListExtension.HasView(list, viewName)); // Try calling the extension method as a static method.
}
}
Console.Read();
}
}
}
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You also can call the extension methods as static methods.
Output with the extension methods
Extension methods in C# 2.0
As I stated in the introduction to this article, the extension methods is a new feature of C# 3.0, and the SharePoint 2007 API is based on .NET Framework 2.0. If you try to use extension methods in a project targeting .NET Framework 2.0, you will get a compiler error when compiling your code, the error text is “Cannot define a new extension method because the compiler required type ‘System.Runtime.CompilerServices.ExtensionAttribute’ cannot be found”. Seems the compiler just needs to resolve ‘System.Runtime.CompilerServices.ExtensionAttribute’ to compile extension methods. So you can introduce your own ‘System.Runtime.CompilerServices.ExtensionAttribute’ class, then it worked correctly!
namespace System.Runtime.CompilerServices
{
[AttributeUsage(AttributeTargets.Method | AttributeTargets.Class | AttributeTargets.Assembly)]
public sealed class ExtensionAttribute : Attribute
{
}
}
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The brilliant workaround explained by Daniel Moth.
The syntax with extension methods is much more streamline and a lot easier to understand. It easier for developers to approach the object model without having to divide their attention between the SharePoint API and custom class libraries.
