DataWindow.PreValidate Method (Typed)

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Return Value

Type: Usual

Tip
Important! This is a callback method used by X#. Normally, it should not be called in your application code.

This method provides some of the functionality of the WHEN clause in classical Xbase @...SAY...GET statements. However, since the GUI approach does not enforce a rigid sequence of data entry but allows the user to move from control to control at random, the logic of enabling and disabling controls must be different. Instead of checking a condition when focus switches into the control (this is too late, a user with a mouse is already on the new control), the system must keep checking on every significant event. DataWindow:Prevalidate() provides some automatic handling of this type of validation (through DataWindow:RegisterConditionalControls()), but it also allows you to insert custom logic by overriding the method. The standard action in DataWindow:Prevalidate() is to call DataWindow:EnableConditionalControls(); if problems exist, it calls DataWindow:DisableConditionalControls(). DataWindow:Prevalidate() is called after the application of the standard validation, allowing the user to replace the default handling, upon success or failure of validation.