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Parameter.Evaluate Method

Updates and returns the value of the Parameter object.

Namespace:  System.Web.UI.WebControls
Assembly:  System.Web (in System.Web.dll)

protected internal virtual Object Evaluate(
	HttpContext context,
	Control control
)

Parameters

context
Type: System.Web.HttpContext

The current HttpContext of the request.

control
Type: System.Web.UI.Control

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

Return Value

Type: System.Object
An object that represents the updated and current value of the parameter.

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.

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;
}

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0, 2.0

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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