rdlc code 39

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The data source controls include any control that implements the IDataSource interface. The .NET Framework includes the following data source controls: SqlDataSource: This data source allows you to connect to any data source that has an ADO.NET data provider. This includes SQL Server, Oracle, and the OLE DB or ODBC data sources, as discussed in 7. When using this data source, you don t need to write the data access code. ObjectDataSource: This data source allows you to connect to a custom data access class, such as the one you saw in 8. This is the preferred approach for large-scale professional web applications. XmlDataSource: This data source allows you to connect to an XML file. You ll learn more in 12. SiteMapDataSource: This data source allows you to connect to the Web.Sitemap file that describes the navigational structure of your website. You ll learn more in 16. You can find all the data source controls in the Data tab of the Toolbox in Visual Studio. Data source controls are new in ASP.NET 2.0, and it s expected that more will become available, both from Microsoft and from third-party vendors. When you drop a data source control onto your web page, it shows up as a gray box in Visual Studio. However, this box won t appear when you run your web application and request the page (see Figure 9-5).

If you ve programmed with ASP.NET 1.x, you ve probably used the similar DataGrid control. Faced with the challenge of enhancing the DataGrid while preserving backward compatibility, the ASP .NET team decided to create an entirely new control to implement their improvements. This control is the GridView. The GridView is an extremely flexible grid control for showing data. It includes a wide range of hard-wired features, including selection, paging, and editing, and it is extensible through templates. The great advantage of the GridView over the DataGrid is its support for code-free scenarios. Using the GridView, you can accomplish many common tasks, such as paging and selection, without writing any code. With the DataGrid, you were forced to handle events to implement the same features.

However, that raises new complications For one thing, the GridView will have already been filled with data based on the initial DropDownList selection (Even if you solve this problem, there are other issues related to how changes are detected in the DropDownList selection) Ultimately, you ll need to resort to programmatic data binding In normal operation, data source controls are invoked automatically when a linked control needs data or is ready to commit an update However, a lesser known fact is that you can also take charge of data source controls programmatically, by calling methods such as Select(), Update(), Insert(), and Delete() Of course, it s up to you to bind the data you retrieve from Select() and supply the changed data for when committing an update To put this into practice, start by removing the DropDownListDataSourceID property .

Data source controls can perform two key tasks: They can retrieve data from a data source and supply it to linked controls They can update the data source when edits take place in linked controls In ASPNET 1x, creating data-bound pages was complicated because you needed to understand the page life cycle, or you risked binding the page at the wrong time Of course, in ASPNET 20 you still need to understand the basics of the page life cycle because you ll run into situations where you need to work with or extend the data binding model For example, you might want to add data or set a selected item in a control after it has been bound to the data source.

The DataGrid is still available in ASP.NET 2.0, and it now supports binding to a data source control. Although you can t find it in the Toolbox, you can add it by right-clicking the Toolbox and selecting Choose Items. As a rule of thumb, the DataGrid should be used only for backward compatibility and existing ASP.NET websites (where it still works quite well). When creating a new website, use the GridView instead.