The System.Web.UI.HtmlControls.HtmlSelect control uses the HtmlSelect.RequiresDataBinding property to determine whether the control needs to call the System.Web.UI.Control.DataBind method to bind to its specified data source.

Each time the set accessor is called on either the HtmlSelect.DataSource, HtmlSelect.DataSourceID, or HtmlSelect.DataMember property to change the data source after the HtmlSelect.OnInit(EventArgs) method has already been called, ASP.NET automatically sets the value of the HtmlSelect.RequiresDataBinding property to true. The value of the HtmlSelect.RequiresDataBinding property is also set to true when the HtmlSelect.OnDataPropertyChanged method is invoked.

ASP.NET automatically sets the value of the HtmlSelect.RequiresDataBinding property to false immediately after the System.Web.UI.Control.DataBind method has been called.