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Applies To

Description

If enabled, this event is generated when the configuration of an object (position and/or size) is about to change.

For a Form, the event is generated when the Form is resized or moved by the user.

For any object other than a Form, it can occur in one of two ways. Firstly, whenever a Form is resized, the system (by default) re-arranges its children so as to maintain their relative position and size. This generates a Configure event (if enabled) for each one of them.

Secondly, it can occur as a result of the user resizing the object directly. This facility is enabled by setting the object's Sizeable property to 1.

Note that a Configure event is not reported when an object is moved using "drag & drop". See Dragable (property) and DragDrop (event) for details of this operation.

The event message reported as the result of ⎕DQ, or supplied as the right argument to your callback function, is a 6-element vector as follows :

For any object, the operation can be prevented by returning a scalar 0 from the callback function associated with the Configure event.

Full-Drag Considerations

The user may choose a system option, described here as full-drag, whereby the contents of the window are re-arranged during a resize operation.

If you manage the geometry of your controls using the Attach property, APL honours full drag during resize, changing the size and position of your controls dynamically for you.

However, if you manage the geometry of controls using Configure event callbacks, you should consider the following.

1. If full drag is in enabled, APL generates Configure events during the resize operation, allowing you to dynamically alter the geometry of controls as you wish. However, the following restrictions apply:
   
   
2. Configure callbacks will only be executed when the interpreter is idle. For example during a ⎕DQ or during Session input (6-space prompt). If the user attempts to move/resize a window that has Configure callbacks attached when the interpreter is busy, the move/resize is not started. This is similar to the operation in non full drag mode, where the move/resize is allowed but the callback does not execute until the interpreter again becomes idle.
   
   
3. The callback cannot be traced. It is necessary to debug the callback code with full drag disabled.
   
   
4. Any untrapped errors in the Configure callback will not halt execution in the normal way, but will instead be reported in the Status Window. Note that it is also not possible to trap such errors higher up the SI stack than the Configure Callback.
   
   
5. There are some programming styles to be avoided if full drag Configure callbacks are to be processed correctly. For example events generated by monadic ⎕NQ within a Configure callback will not be processed until the entire resize operation has been completed.
   
   
6. It is not possible to save a workspace from within a Configure Callback in full drag mode.

The above restrictions apply to Configure events when full drag is enabled, but only when full drag is enabled. The behaviour of Configure callbacks with full drag disabled is the same as for other events.