Replace a WebPart with new one in SharePoint

using (SPSite spSiteTest = new SPSite(webURL))

           {

               SPFile file = null;

               using (SPWeb web = spSiteTest.OpenWeb())

               {

                   try

                   {

                       file = web.GetFile(webPageURL);

                       if (file.Level == SPFileLevel.Checkout)

                       {

                           file.CheckIn("Checkin before replace");

                           file.CheckOut();

                       }

                       else

                       {

                           file.CheckOut();

                       }

                       SPLimitedWebPartManager webPartMgr = file.GetLimitedWebPartManager(System.Web.UI.WebControls.WebParts.PersonalizationScope.Shared);

                       for (int k = 0; k < webPartMgr.WebParts.Count; k++)

                       {

                           System.Web.UI.WebControls.WebParts.WebPart wpOld = webPartMgr.WebParts[k];

                           if (string.Compare(wpOld.GetType().Name.Trim(), webPartName.Trim(), true) == 0)

                           {

                               //Read old webpart properties

                               string zoneID = webPartMgr.GetZoneID(wpOld);

                               string storageKey = webPartMgr.GetStorageKey(wpOld).ToString();

                               //create new webpart object            

                               MyNewWebPart wpNew = new MyNewWebPart();

                               wpNew.Title = wpOld.Title;// "Web Part Title";

                               wpNew.ChromeState = wpOld.ChromeState;// System.Web.UI.WebControls.WebParts.PartChromeState.Normal;

                               wpNew.ChromeType = wpOld.ChromeType;// System.Web.UI.WebControls.WebParts.PartChromeType.None;

                               webPartMgr.DeleteWebPart(wpOld);

                               //Add new webpart object to webparts collection     

                               webPartMgr.AddWebPart(wpNew, zoneID, 0);

                               file.Update();

                               web.Update();

                           }

                       }

                   }

                   catch (Exception ex)

                   {

                       if (file != null && file.Level == SPFileLevel.Checkout)

                       {

                           file.UndoCheckOut();

                       }

                   }

                   finally

                   {

                       if (file != null && file.Level == SPFileLevel.Checkout)

                       {

                           file.CheckIn("Added");

                       }

                       web.AllowUnsafeUpdates = false;

                   }

               }

           }

Get a List of Site Collections in a Web Application in SharePoint

            

               SPWebApplication webApp = SPWebApplication.Lookup(new Uri(“WebApplication URL”));

               foreach (SPSite site in webApp.Sites)
               {
                   radCmbSiteCollList.Items.Add(new RadComboBoxItem(site.Url));
                   site.Dispose();
               }

Get a List of Web Applications in a SharePoint Farm

Code to iterate through all the web applications in a SharePoint Farm         

              SPFarm farm = SPWebService.ContentService.Farm;
               SPWebApplicationCollection webAppColl = SPWebService.ContentService.WebApplications;
               if (webAppColl != null)
               {
                   foreach (SPWebApplication spWebApp in webAppColl)
                   {
                       lst.Items.Add(new ListItem(spWebApp.AlternateUrls[0].Uri.ToString()));
                   }
                   radCmbWebApplications.Items.Insert(0, new RadComboBoxItem(" -- Select a WebApplication -- ", "-1"));

               }