| True DataControl 8.0 Reference > Parameter Object > Parameter Object Properties > ValueExpression Property (Parameter) |
ValueExpression Property (Parameter)
Specifies the expression used to calculate the value of a parameter.
Parameter.ValueExpression= variant
Read/Write at run time and design time. Property applies to Parameter object.
This property specifies the expression that provides the parameter value.
If this property is left empty, the parameter value can still be set in code.
True DataControl evaluates this expression when the TData control is loaded, and on every refresh, before populating the Recordset, because parameter values can influence recordset contents.
Asynchronous evaluation of this expression, triggered by a change of a variable in it, can cause a refresh. It happens when the parameter is used in an expression causing a refresh, such as a range condition or filter expression.
See True DataControl Parameters for more information.
See True DataControl Expressions for more information about expressions in general. Evaluation rules for ValueExpression are as follows:
Expression Level: Recordset level
Synchronous Evaluation: Evaluated before the recordset is populated with records.
Asynchronous Evaluation: Action depends on whether or not the parameter is used in an expression forcing refresh. If so, changing the parameter value forces refresh.
See Also