Ajax Method

public class AjaxMethods
{
[Ajax.AjaxMethod(Ajax.HttpSessionStateRequirement.ReadWrite)]
public void CurrentFolder(string value)
{
HttpContext.Current.Session["CurrentFolder"] = value;
}
public bool IsExistsImageFile(string folderPath)
{
bool fileOK = false;
String[] allowedExtensions = { ".gif", ".png", ".jpeg", ".jpg" };
if (folderPath != Null.NullString)
{
String fileExtension = System.IO.Path.GetExtension(folderPath).ToLower();
for (int i = 0; i < allowedExtensions.Length; i++)
{
if (fileExtension == allowedExtensions[i])
{
fileOK = true;
}
}
}
return fileOK;
}
}