[Overview][Constants][Types][Classes][Procedures and functions][Index] | Reference for unit 'ComCtrls' (#lcl)

# TCustomUpDown.OnChanging

Event handler signalled prior to changing the value in the Position property.

## Declaration

Source position: comctrls.pp line 1999

`protected property TCustomUpDown.OnChanging : TUDChangingEvent read FOnChanging write FOnChanging;`

## Description

OnChanging is a TUDChangingEvent property with the event handler signalled prior to setting a new value for the Position property. The handler include a Boolean AllowChange argument which indicates if a change to the Position property is allowed in the control. Setting AllowChange to False in the handler routine prevents a change from being applied to the property value.

OnChanging is signalled (when assigned) from CanChange, and is used to get the return value for the method. It allows the application to accept or reject a change to Position using logic specific to the application.

Use OnChangingEx to implement an event handler which examines the new property value and direction (increase or decrease) for the changed value.

## See also

TCustomUpDown.CanChange |  | Indicates whether a change using the control can be applied.
TCustomUpDown.Position |  | The current position (or value) for the control as a SmallInt type.
TCustomUpDown.OnChangingEx |  | Event handler signalled to determine if the control can change the value in the Position property.
TUDChangingEvent |  | Specifies an event handler signalled prior to changing the value in a TUpDown control.