How to Use the Load, Init, Destroy, and Unload Events (136695)

SUMMARY

This article explains the sequence of the Load, Init, Destroy, and Unload events, and it gives points to consider when writing user code for these events. The Load event occurs before the controls on a form are created, whereas the Init event occurs after the controls on a form are created. When a form is released, the Destroy event occurs before the controls on a form are released, and the Unload event occurs after the controls on a form are released.

MORE INFORMATION

Load Event

The Load event occurs before any controls are created. That means the form's Load event procedure must not reference any of the controls.

The form's Load event procedure is a good place to:

Define any global variables that the controls need to refer to in their Init events
Open any tables or queries not in the data environment.
Call the OpenTables of the data environment if the AutoOpenTables property of the data environment is set to False (.F.). If the data environment's AutoOpenTables property is set to True (.T.), the tables and views will already be open when the form's Load event occurs.

Init Event

The form's Init event occurs after all the controls are created, so you can refer to any control on a form in the form's Init event procedure. If certain controls should be disabled or have certain values specified, the form's Init code is a good place to assign values to controls or disable them. The form's Init event has not yet occurred when the controls are created, so any variables that a control's Init event code needs should not be set in the form's Init method.

Destroy Event

The form's Destroy event occurs before the controls on a form are released, so you can refer to the controls in the form's Destroy event. For example, code that stores the value left in an unbound control can be placed in the form's Destroy event. The controls have not yet been released, so any tables that the controls refer to should not be closed in the form's Destroy event code.

Unload Event

The Unload event occurs after the controls are released. The code in the Unload event of a form cannot refer to the controls on the form because they do not exist when the Unload event fires. Because the controls no longer exist, the Unload event code is a safe place to close any tables or release memory variables that any controls used. If the data environment's AutoCloseTables property is set to False (.F.), the form's Unload event code is a good place to call the data environment's CloseTables method. If the data environment's AutoCloseTables property is set to True (.T.), the tables and views will be closed after the form's Unload method is completed.