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LSPS Documentation
Event Processing

When the user or the system performs an action on a form component, the form component produces an event of a certain type. The type is defined by the action that caused it.

If the form component has a listener for the type of the event, the event triggers the event-processing cycle (An exception are the non-immediate ValueChangeEvents. These events are queued and processed later when an immediate event appears.)

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Form event firing

An event is processed in the event-processing cycle, or request-response cycle. and the exact way it is processed is defined by its listeners.

Here is a simplified descriptions of the cycle (we omit here the case when there are non-immediate ValueChangeEvents in the queue):

  1. An event is thrown.
  2. All listeners catch the event.
  3. All error messages in the form are cleared.
  4. Event is processed based on the listener properties:
    • Internal values in the form, the values referenced by the bindings of form components, are updated.
    • Internal values are validated.
    • The handle expressions of listeners are executed.
    • Application events.
    • View Models are merged or cleared.
    • The Navigation expression is calculated.
  5. Components are refreshed: If a new event arises as a result, the whole processing is repeated. If no event arises, the processing continues to listener actions:
    • Submit: defines if the document or to-do is submitted as part of the event handling;
    • Persist: if enabled, the relevant data in the processed components is persisted as part of the event handling; unlike on submit action, if the form is used by a to-do, the to-do does not become finished; if part of a document, the document remains open; persist is performed after the merge to the screen level before the transaction is committed.
    • Save action: defines if the to-do or document is saved;
    • Navigation: defines the location where to navigate after the event is processed; you can navigate to a to-do or document, URL, custom application page (refer to the descriptions of the data types defined in the human.navigation.datatypes resource in the Standard Library)
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Event processing cycle
The event processing and the listener actions are executed within a single database transaction so that if the processing fails at any stage, the database is rolled back to a consistent state.

simpleRequestResponseProcessedComponents.png
Database transaction on event processing and listener actions
You can find a detailed schema of the cycle here.

Events Listeners