Parameter.Evaluate(HttpContext, Control) Parameter.Evaluate(HttpContext, Control) Parameter.Evaluate(HttpContext, Control) Method

Definition

Updates and returns the value of the Parameter object.

protected public:
 virtual System::Object ^ Evaluate(System::Web::HttpContext ^ context, System::Web::UI::Control ^ control);
protected internal virtual object Evaluate (System.Web.HttpContext context, System.Web.UI.Control control);
abstract member Evaluate : System.Web.HttpContext * System.Web.UI.Control -> obj
override this.Evaluate : System.Web.HttpContext * System.Web.UI.Control -> obj

Parameters

context
HttpContext HttpContext HttpContext

The current HttpContext of the request.

control
Control Control Control

The Control the parameter is bound to. If the parameter is not bound to a control, the control parameter is ignored.

Returns

An object that represents the updated and current value of the parameter.

Examples

The following code example demonstrates how to override the Evaluate method to return the correct value in a class that is derived from the Parameter class. This code example is part of a larger example provided for the Parameter class overview.

// The Evaluate method is overridden to return the
// DataValue property instead of the DefaultValue.
protected override object Evaluate(HttpContext context, Control control) {

  if (context.Request == null)
      return null;

  return DataValue;
}
' The Evaluate method is overridden to return the
' DataValue property instead of the DefaultValue.
Protected Overrides Function Evaluate(context As HttpContext, control As Control) As Object
   If context Is Nothing Then
       Return Nothing
   Else
       Return DataValue
   End If
End Function

Remarks

The default implementation of the Evaluate method is to return null in all cases. Classes that derive from the Parameter class override the Evaluate method to return an updated parameter value. For example, the ControlParameter object returns the value of the control that it is bound to, while the QueryStringParameter object retrieves the current name/value pair from the HttpRequest object.

Applies to