Form Events

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	Code	Object Methods	Form Method	Which Objects
On Activate	11	Never	Yes	None
On After Edit	45	Yes	Yes	Involved object only
On After Keystroke	28	Yes	Yes	Involved object only
On After Sort	30	Yes (List box)	Never	Involved object only
On Alternative Click	38	Yes (Button and List box)	Never	Involved object only
On Before Data Entry	41	Yes (List box)	Never	Involved object only
On Before Keystroke	17	Yes	Yes	Involved object only
On Begin Drag Over	46	Yes	Yes	Involved object only
On Begin URL Loading	47	Yes (Web Area)	Never	Involved object only
On Bound variable change	54	Never	Yes	None
On Clicked	4	Yes	Yes	Involved object only
On Close Box	22	Never	Yes	None
On Close Detail	26	Yes (List box)	Yes	None except List boxes
On Collapse	44	Yes (Hier. list and list box)	Never	Involved object only
On Column Moved	32	Yes (List box)	Never	Involved object only
On Column Resize	33	Yes (List box and 4D View Pro Area)	Never	Involved object only
On Data Change	20	Yes	Yes	Involved object only
On Deactivate	12	Never	Yes	None
On Delete Action	58	Yes (Hier. list and list box)	Never	Involved object only
On Display Detail	8	Yes	Yes	All objects
On Double Clicked	13	Yes	Yes	Involved object only
On Drag Over	21	Yes	Never	Involved object only
On Drop	16	Yes	Yes	Involved object only
On End URL Loading	49	Yes (Web Area)	Never	Involved object only
On Expand	43	Yes (Hier. list and list box)	Never	Involved object only
On Footer Click	57	Yes (List box)	Never	Involved object only
On Getting Focus	15	Yes	Yes	Involved object only
On Header	5	Yes	Yes	All objects
On Header Click	42	Yes (List box and 4D View Pro Area)	Never	Involved object only
On Load	1	Yes	Yes	All objects
On Load Record	40	Never	Yes	None
On Long Click	39	Yes (Button)	Yes	Involved object only
On Losing Focus	14	Yes	Yes	Involved object only
On Menu Selected	18	Never	Yes	None
On Mouse Enter	35	Yes	Yes	All objects
On Mouse Leave	36	Yes	Yes	All objects
On Mouse Move	37	Yes	Yes	All objects
On Mouse Up	2	Yes	Never	Involved object only
On Open Detail	25	Yes (List box)	Yes	None except List boxes
On Open External Link	52	Yes (Web Area)	Never	Involved object only
On Outside Call	10	Never	Yes	None
On Page Change	56	Never	Yes	None
On Plug in Area	19	Yes	Yes	Involved object only
On Printing Break	6	Yes	Yes	All objects
On Printing Detail	23	Yes	Yes	All objects
On Printing Footer	7	Yes	Yes	All objects
On Resize	29	Never	Yes	None
On Row Moved	34	Yes (List box)	Never	Involved object only
On Row Resize	60	Yes (4D View Pro Area)	Never	Involved object only
On Scroll	59	Yes	Never	Involved object only
On Selection Change	31	Yes	Yes	Involved object only
On Timer	27	Never	Yes	None
On Unload	24	Yes	Yes	All objects
On URL Filtering	51	Yes (Web Area)	Never	Involved object only
On URL Loading Error	50	Yes (Web Area)	Never	Involved object only
On URL Resource Loading	48	Yes (Web Area)	Never	Involved object only
On Validate	3	Yes	Yes	All objects
On VP Range Changed	61	Yes (4D View Pro Area)	Never	Involved object only
On VP Ready	9	Yes (4D View Pro Area)	Never	Involved object only
On Window Opening Denied	53	Yes (Web 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.