ASP.NET Data Binding

ASP.NET data binding differs dramatically from Windows Forms data binding. The key difference is that ASP.NET data binding takes place on the server side when the page is loaded. However, there is no mechanism to apply the data binding to the rendered HTML page that is sent to the user. Thus, there is no way to implement synchronized controls or editable data objects (although this can be simulated). ASP.NET binding is strictly one-way; data can flow from a DataSet into a control but not vice versa.

Because of a web application’s stateless nature, ASP.NET data binding is less powerful than Windows Forms data binding. However, ASP.NET makes up for the loss by including several advanced template-based controls, such as the DataGrid, DataList, and Repeater. These controls have a much more customizable interface and offer many features the Windows DataGrid doesn’t.

The data binding process in an ASP.NET page works like this:

1. You define the bindings, using similar syntax to what you use when binding a Windows form.

2. You trigger data binding for individual controls or the entire page by calling the DataBind( ) method. At this point, the information moves from the data objects to the controls.

3. The final page is rendered to HTML. The data objects are discarded.

4. The page is posted back at a later point, perhaps in response to an editing action the user has performed with a data-bound control. At this point, you must requery the database, re-create the ADO.NET objects, and rebind the page before returning it to the user. Optionally, your program can issue an update statement to the database.

It helps to think of ASP.NET data binding as a quick and flexible way to populate controls with information from a database. It can’t create the same sort of "record-browsers" that are possible with Windows Forms because there is no synchronization method for the controls. To implement functionality similar to what is available in Windows Forms, you have to handle control events and continuously post back the page whenever a selection changed.