Swap page layout for page,sharepoint 2010

This exercise demonstrates how to change the pagelayout with the new pagelayout.

public static void SwapPageLayout(PublishingWeb publishingWeb, PageLayout oldPageLayout, PageLayout newPageLayout)

        {

            // Replace these variable values and input parameters

            // with your own values.

            //

            // The comment to set when the page is checked in, published, and

            // approved.

            string checkInComment = "Your comments";

            //

            // Validate the input parameters.

            if (null == publishingWeb)

            {

                throw new System.ArgumentNullException("publishingWeb");

            }

            if (null == oldPageLayout)

            {

                throw new System.ArgumentNullException("oldPageLayout");

            }

            if (null == newPageLayout)

            {

                throw new System.ArgumentNullException("newPageLayout");

            }

            // Confirm that the oldPageLayout and newPageLayout are compatible.

            if (oldPageLayout.AssociatedContentType.Id != newPageLayout.AssociatedContentType.Id)

            {

                throw new System.ArgumentException(

                    "The page layouts must render the same type of content",

                    "newPageLayout");

            }

            System.Guid oldPageLayoutId = oldPageLayout.ListItem.File.UniqueId;

            // Set the new PageLayout for all pages that use the old PageLayout.

            PublishingPageCollection publishingPages = publishingWeb.GetPublishingPages();

            foreach (PublishingPage publishingPage in publishingPages)

            {

                if (publishingPage.Layout.ListItem.UniqueId == oldPageLayoutId)

                {

                    if (publishingPage.ListItem.File.CheckOutStatus == SPFile.SPCheckOutStatus.None)

                    {

                        publishingPage.CheckOut();

                    }

                    publishingPage.Layout = newPageLayout;

                    publishingPage.Update();

                    // The PublishingPage has the same SPContentType as its PageLayout.

                    System.Diagnostics.Debug.Assert(

                        publishingPage.ContentType.Parent.Id ==

                        newPageLayout.AssociatedContentType.Id);

                    publishingPage.CheckIn(checkInComment);

                }

            }

        }