How to programmatically add delete modify item permissions in SharePoint 2013

Note: SPPrincipal can be either an SPUser or SPGroup Object

Breaking Inheritance

//specifies whether the item has unique security

//or inherits its role assignments from a parent object.

item.HasUniqueRoleAssignments

//Stops inheriting permissions from parent object

// if true, it will keep all existing users

// false, to remove all users

item.BreakRoleInheritance(true);

//Removes the local role assignments

//and reverts to role assignments from the parent object.

item.ResetRoleInheritance();

Adding Permissions to an item

//SPGroup group = web.Groups[0];

//SPUser user = web.Users[0];

//SPUser user2 = web.EnsureUser("mangaldas.mano");

//SPUser user3 = web.EnsureUser("Domain Users"); ;

//SPPrincipal[] principals = { group, user, user2, user3 };

public static void SetPermissions(this SPListItem item, IEnumerable principals, SPRoleType roleType)

{

 if (item != null)

 {

  foreach (SPPrincipal principal in principals)

  {

   SPRoleDefinition roleDefinition = item.Web.RoleDefinitions.GetByType(roleType);

   SetPermissions(item, principal, roleDefinition);

  }

 }

}

public static void SetPermissions(this SPListItem item, SPUser user, SPRoleType roleType)

{

 if (item != null)

 {

  SPRoleDefinition roleDefinition = item.Web.RoleDefinitions.GetByType(roleType);

  SetPermissions(item, (SPPrincipal)user, roleDefinition);

 }

}

public static void SetPermissions(this SPListItem item, SPPrincipal principal, SPRoleType roleType)

{

 if (item != null)

 {

  SPRoleDefinition roleDefinition = item.Web.RoleDefinitions.GetByType(roleType);

  SetPermissions(item, principal, roleDefinition);

 }

}

public static void SetPermissions(this SPListItem item, SPUser user, SPRoleDefinition roleDefinition)

{

 if (item != null)

 {

  SetPermissions(item, (SPPrincipal)user, roleDefinition);

 }

}

public static void SetPermissions(this SPListItem item, SPPrincipal principal, SPRoleDefinition roleDefinition)

{

 if (item != null)

 {

  SPRoleAssignment roleAssignment = new SPRoleAssignment(principal);

  roleAssignment.RoleDefinitionBindings.Add(roleDefinition);

  item.RoleAssignments.Add(roleAssignment);

 }

}

Deleting all user Permissions from an item

public static void RemovePermissions(this SPListItem item, SPUser user)

{

 if (item != null)

 {

  RemovePermissions(item, user as SPPrincipal);

 }

}

public static void RemovePermissions(this SPListItem item, SPPrincipal principal)

{

 if (item != null)

 {

  item.RoleAssignments.Remove(principal);

  item.SystemUpdate();

 }

}

Removing specific roles from an item

public static void RemovePermissionsSpecificRole(this SPListItem item, SPPrincipal principal, SPRoleDefinition roleDefinition)

{

 if (item != null)

 {

  SPRoleAssignment roleAssignment = item.RoleAssignments.GetAssignmentByPrincipal(principal);

  if (roleAssignment != null)

  {

   if (roleAssignment.RoleDefinitionBindings.Contains(roleDefinition))

   {

    roleAssignment.RoleDefinitionBindings.Remove(roleDefinition);

    roleAssignment.Update();

   }

  }

 }

}

public static void RemovePermissionsSpecificRole(this SPListItem item, SPPrincipal principal, SPRoleType roleType)

{

 if (item != null)

 {

  SPRoleDefinition roleDefinition = item.Web.RoleDefinitions.GetByType(roleType);

  RemovePermissionsSpecificRole(item, principal, roleDefinition);

 }

}

Updating or Modifying Permissions on an item

public static void ChangePermissions(this SPListItem item, SPPrincipal principal, SPRoleType roleType)

{

 if (item != null)

 {

  SPRoleDefinition roleDefinition = item.Web.RoleDefinitions.GetByType(roleType);

  ChangePermissions(item, principal, roleDefinition);

 }

}

public static void ChangePermissions(this SPListItem item, SPPrincipal principal, SPRoleDefinition roleDefinition)

{

 SPRoleAssignment roleAssignment = item.RoleAssignments.GetAssignmentByPrincipal(principal);

 if (roleAssignment != null)

 {

  roleAssignment.RoleDefinitionBindings.RemoveAll();

  roleAssignment.RoleDefinitionBindings.Add(roleDefinition);

  roleAssignment.Update();

 }

}