A DataView is a powerful webpart which provides a larget set of data sources including SharePoint lists, xml files and even web services. A dataview can be fully customized using xslt, for example, to display data in a drop down list instead of data grid. The significant drawback, in my opinion, is that you can add and modify a dataview only through a SharePoint desginer. The problem with using a SharePoint designer for a DataView is that, first of all, it is difficult to deploy a DataView from one environment to another, i.e. from dev server to test, from test to pre-production, from pre-production to production because the datasource that a DataView stores contains GUID of a SharePoint list if a SharePoint list is used as a data source.

Another scenario where using a SharePoint designer is limited is of using a DataView for personal views. Let's say I want to display personalized query for each user using a DataView.

The solution is to create or modify a DataView programmatically. A DataView internally uses a "DataFormWebPart" class.

Here is a code snipet:

using Microsoft.SharePoint;
using Microsoft.SharePoint.WebControls;
using wsswp = Microsoft.SharePoint.WebPartPages;
using System.Web.UI.WebControls.WebParts;
....
....
....

// Create or Update a DataView programmatically
bool CreateOrUpdateDataViewWebpart(string webUrl, string listName, string pageUrl,
            string xslLink,
            string zoneName,
            string webPartName,
            string titleUrl,
            bool needsUpdate,
            string query,
            uint index,
            uint maximumRow,
            PersonalizationScope personalizationScope
)

{
            bool viewCreatedOrUpdated = false;
            WebPart wp = null;

            wsswp.DataFormWebPart dataFormWebPart = null;

            using (SPSite site = new SPSite(webUrl))
            using (SPWeb web = site.OpenWeb())
            {
                web.AllowUnsafeUpdates = true;
                SPList list = web.Lists[listName];

                wsswp.SPLimitedWebPartManager wpManager = web.GetLimitedWebPartManager(pageUrl, personalizationScope);

                foreach (WebPart wpTemp in wpManager.WebParts)
                {
                    if (String.Compare(webPartName, wpTemp.Title, true) == 0)
                    {
                        wp = wpTemp;
                        break;
                    }
                }

                string dataSourceId =  webPartName;
                if (wp == null)
                {
                   // Create a webpart
                    dataFormWebPart = new wsswp.DataFormWebPart();

                    dataFormWebPart.TitleUrl = titleUrl;
                    dataFormWebPart.ZoneID = zoneName;
                    dataFormWebPart.Title = webPartName;
                    dataFormWebPart.XslLink = xslLink;
                    SPDataSource dataSource = GetDataSource(dataSourceId, webUrl, list, query, maximumRow);
                    dataFormWebPart.DataSources.Add(dataSource);
                   
                    wpManager.AddWebPart(dataFormWebPart, webPartName, index);
                    viewCreatedOrUpdated  = true;

                 }
                else
                {
                   // Update an existing webpart
                    if (needsUpdate)
                    {
                            dataFormWebPart = (wsswp.DataFormWebPart)wp;
                            dataFormWebPart.TitleUrl = titleUrl;
                            dataFormWebPart.DataSourceID = string.Empty;
                            SPDataSource dataSource = GetDataSource(dataSourceId, webUrl, list, query, maximumRow);
                            dataFormWebPart.DataSources.Clear();
                            dataFormWebPart.DataSources.Add(dataSource);
                            wpManager.SaveChanges(dataFormWebPart);
                            viewCreatedOrUpdated  = true;
                    }
                }
    return viewCreatedOrUpdated;

}

       // Return a SharePoint list filtered by query as a data source 
       SPDataSource GetDataSource(string dataSourceId, string webUrl, SPList list, string query, uint maximumRow)
        {
            SPDataSource dataSource = new SPDataSource();
            dataSource.UseInternalName = true;
            dataSource.ID = dataSourceId;
            dataSource.DataSourceMode = SPDataSourceMode.List;
            dataSource.List = list;
            dataSource.SelectCommand = "<View>" + query + "</View>";

            Parameter listIdParam = new Parameter("ListID");
            listIdParam.DefaultValue = list.ID.ToString("B").ToUpper();

            Parameter maximumRowsParam = new Parameter("MaximumRows");
            maximumRowsParam.DefaultValue = maximumRow.ToString();

            QueryStringParameter rootFolderParam = new QueryStringParameter("RootFolder", "RootFolder");

            dataSource.SelectParameters.Add(listIdParam);
            dataSource.SelectParameters.Add(maximumRowsParam);
            dataSource.SelectParameters.Add(rootFolderParam);

            dataSource.UpdateParameters.Add(listIdParam);
            dataSource.DeleteParameters.Add(listIdParam);
            dataSource.InsertParameters.Add(listIdParam);

            return dataSource;
        }

query can be an empty string. the query will contain a SPQuery string contained in "<Query>...</Query>." For example, the full query will look like this:

"<Query><Where><Eq><FieldRef Name='Status'/><Value Type='Text'>Completed</Value></Eq></Where></Query>";

PersonalizationScope will be either PersonalizationScope.Shared or PersonalizationScope.User.