Overview

Form events are events that can lead to the execution of the form method and/or form object method(s). Form events allow you to control the flow of your application and to write code that is executed only when a specific event occurs.

In your code, you control the events using the FORM Event command, that returns the triggered event. For example:

//code of a button
If(FORM Event.code=On Clicked) 
// do something when the button is clicked
End if

Every form and every active object on the form can listen to a predefined set of events, but only the events that you enabled at the form level and/or at every object level will actually occur.

Event object

Each event is returned as an object by the FORM Event command. By default, it contains the following properties:

Property	Type	Description
objectName	text	Name of the object triggering the event - Not included if the event is triggered by the form
code	longint	Numeric value of the form event. Also returned by the Form event code command
description	text	Name of the form event (e.g. "On After Edit")

Additional properties are returned when the event occurs on specific objects. In particular:

• list boxes and list box columns return additional properties such as columnName or isRowSelected.
• 4D View Pro areas return for example sheetName or action properties in the On After Edit event object.

Events and Methods

When a form event occurs, 4D performs the following actions:

• First, it browses the objects of the form and calls the object method for any object (involved in the event) whose corresponding object event property has been selected.
• Second, it calls the form method if the corresponding form event property has been selected.

Do not assume that the object methods, if any, will be called in a particular order. The rule of thumb is that the object methods are always called before the form method. If an object is a subform, the object methods of the subform’s list form are called, then the form method of the list form is called. 4D then continues to call the object methods of the parent form. In other words, when an object is a subform, 4D uses the same rule of thumb for the object and form methods within the subform object.

Except for the On Load and On Unload events (see below), if the form event property is not selected for a given event, this does not prevent calls to object methods for the objects whose same event property is selected. In other words, enabling or disabling an event at the form level has no effect on the object event properties.

The number of objects involved in an event depends on the nature of the event.

Call Table

The following table summarizes how object and form methods are called for each event type:

Event	Object Methods	Form Method	Which Objects
On Load	Yes	Yes	All objects
On Unload	Yes	Yes	All objects
On Validate	Yes	Yes	All objects
On Clicked	Yes	Yes	Involved object only
On Double Clicked	Yes	Yes	Involved object only
On Before Keystroke	Yes	Yes	Involved object only
On After Keystroke	Yes	Yes	Involved object only
On After Edit	Yes	Yes	Involved object only
On Getting Focus	Yes	Yes	Involved object only
On Losing Focus	Yes	Yes	Involved object only
On Activate	Never	Yes	None
On Deactivate	Never	Yes	None
On Outside Call	Never	Yes	None
On Page Change	Never	Yes	None
On Begin Drag Over	Yes	Yes	Involved object only
On Drop	Yes	Yes	Involved object only
On Drag Over	Yes	Never	Involved object only
On Mouse Enter	Yes	Yes	All objects
On Mouse Move	Yes	Yes	All objects
On Mouse Leave	Yes	Yes	All objects
On Mouse Up	Yes	Never	Involved object only
On Menu Selected	Never	Yes	None
On Bound variable change	Never	Yes	None
On Data Change	Yes	Yes	Involved object only
On Plug in Area	Yes	Yes	Involved object only
On Header	Yes	Yes	All objects
On Printing Detail	Yes	Yes	All objects
On Printing Break	Yes	Yes	All objects
On Printing Footer	Yes	Yes	All objects
On Close Box	Never	Yes	None
On Display Detail	Yes	Yes	All objects
On Open Detail	Yes (List box)	Yes	None except List boxes
On Close Detail	Yes (List box)	Yes	None except List boxes
On Resize	Never	Yes	None
On Selection Change	Yes	Yes	Involved object only
On Load Record	Never	Yes	None
On Timer	Never	Yes	None
On Scroll	Yes	Never	Involved object only
On Before Data Entry	Yes (List box)	Never	Involved object only
On Column Moved	Yes (List box)	Never	Involved object only
On Row Moved	Yes (List box)	Never	Involved object only
On Column Resize	Yes (List box and 4D View Pro Area)	Never	Involved object only
On Header Click	Yes (List box and 4D View Pro Area)	Never	Involved object only
On Footer Click	Yes (List box)	Never	Involved object only
On After Sort	Yes (List box)	Never	Involved object only
On Long Click	Yes (Button)	Yes	Involved object only
On Alternative Click	Yes (Button and List box)	Never	Involved object only
On Expand	Yes (Hier. list and list box)	Never	Involved object only
On Collapse	Yes (Hier. list and list box)	Never	Involved object only
On Delete Action	Yes (Hier. list and list box)	Never	Involved object only
On URL Resource Loading	Yes (Web Area)	Never	Involved object only
On Begin URL Loading	Yes (Web Area)	Never	Involved object only
On URL Loading Error	Yes (Web Area)	Never	Involved object only
On URL Filtering	Yes (Web Area)	Never	Involved object only
On End URL Loading	Yes (Web Area)	Never	Involved object only
On Open External Link	Yes (Web Area)	Never	Involved object only
On Window Opening Denied	Yes (Web Area)	Never	Involved object only
On VP Range Changed	Yes (4D View Pro Area)	Never	Involved object only
On VP Ready	Yes (4D View Pro Area)	Never	Involved object only
On Row Resize	Yes (4D View Pro Area)	Never	Involved object only

Always keep in mind that, for any event, the method of a form or an object is called if the corresponding event property is selected for the form or objects. The benefit of disabling events in the Design environment (using the Property List of the Form editor) is that you can reduce the number of calls to methods and therefore significantly optimize the execution speed of your forms.

WARNING: The On Load and On Unload events are generated for objects if they are enabled for both the objects and the form to which the objects belong. If the events are enabled for objects only, they will not occur; these two events must also be enabled at the form level.