GUIBaseContext :: doBeforeStoreData - Pre-event handler for Store-data events

The handler is a reaction on the DEV_Store event, which is generated before instance in a control is stored to property handle instance area or when explicitly calling the StoreEntry action. The handler is typically used to perform consistency checks before storing data. When the handle is called, the data in the property handle still contains the old value, while GetText() returns the updated value from the control.

The event handler may prevent data from being stored by returning 1. To display the old value in the application, FillData() can be called.

The handler should return one of the following values:

• -1 (not handled) - the event handler will be removed from the handler list and is not called anymore.
• 1 (refuse) - Requested action will not be executed.
• 0 (ok) - Action is permitted to be executed.