Assigning permission programmatically for document libray or list item sharepoint 2010 code sp 2010

How to access or Assigning permission dynamically to Document library / List library / List Item / picture library on folder in sharepoint 2007 / 2010 ( SP 2010 ) code :

Windows SharePoint 2010 / 2007 provides Services manages permissions through Roles and Responsibilities. SPRoleDefinition and SPRoleDefinition classes provides methods to assign users to roles such as “Contributor” or “Site Owner” or “Reader.

Sample solution code:

Following code demonstrate how to assigning / access “Reader” to custom SharePoint group “customgroup” programmatically on Folder of a document library for a custom sharepoint group by code method

using (SPSite site = new SPSite(siteCollection))
{
  using (SPWeb web = site.OpenWeb(siteName))
  {
    SPDocumentLibrary docLib = (SPDocumentLibrary)web.Lists[libraryName];
    //Get folder
    SPListItem item = docLib.Folders[1];
    if (!item.HasUniqueRoleAssignments)
      item.BreakRoleInheritance(true);
    SPRoleAssignment roleAssignment = new SPRoleAssignment(“customgroup”);
    SPRoleDefinition roleDefination = web.RoleDefinitions["Reader "];
    roleAssignment.RoleDefinitionBindings.Add(roleDefination);
    item.RoleAssignments.Add(roleAssignment);
    item.Update();
  }

}