System Triggers

System triggers are script modules that are synchronously executed in response to system events initiated by commands.

Components, application shells, entities, and fields each have an associated set of system triggers.

Uniface provides default definitions for some system triggers of entities, fields, and components. For the most part, these implementations ensure that data can be correctly stored, retrieved, and displayed. In the case of web-based components, they also provide default state management and communication processing.

System triggers are fired as a result of system events that are triggered by commands such as read, delete, or validate. Such commands can cause a cascade of triggers to be fired, especially when validating data or writing to the database. For more information, see Trigger Activation.

Most triggers have no default behavior, so if a trigger event occurs but the associated trigger is not defined, no action is performed.

For a small number of triggers, if the trigger is not defined at a lower level, such as a field, Uniface searches for the trigger definition at the higher level, such as an entity. This provides a fallback mechanism for event handling. These triggers include the receiveMessage (components and application shells), userKey triggers (available for components and application shells), and error (available for fields and entities).

System Trigger Names

System Triggers per Object
Object	System Triggers	Remarks
Application shells	apStart preRequest postRequest receiveMessage quit	Application shell triggers define actions that occur during the lifetime of the application.
Components	accept preActivate postActivate receiveMessage quit	Component-level triggers define actions that typically handle processing when the component is left in a positive or negative manner. Note: The exec operation, and accept and quit triggers are treated as public operations which are always declared as interfaces in a component signature. This ensures that both Uniface and other components can invoke these actions.
Entities	delete deleteUp error lock read preDeserialize postDeserialize preSerialize postSerialize validate validateKey write writeUp	Entity-level triggers define actions affecting entity occurrences, such as adding, modifying, and removing them.
Fields	error formatToDbms formatFromDbms formatToDisplay formatFromDisplay validate	Field-level triggers define the actions to be taken at the field level.
Headers, trailers, break frames	getFocus	Page formatting triggers define how forms and reports are printed.
Headers, trailers, break frames Menus, Menu Options	preDisplay option	Use menu triggers to control the appearance of menu items before they are displayed and the action they perform when selected.