TControlScrollBar.ScrollHandler

Handler for scroll bar movement messages.

Declaration

Source position: forms.pp line 127

Arguments

Description

ScrollHandler is a method used to ensure that the control message in Message is applied to the Position property for the scroll bar. ScrollHandler uses the ScrollCode member from the TLMScroll instance to determine the actions needed in the method. It handles the following ScrollCode values:

SB_LINEUP

Decreases Position by the value in Increment.

SB_LINEDOWN

Increases Position by the value in Increment.

SB_PAGEUP

Decreases Position by the value in Page.

SB_PAGEDOWN

Increases Position by the value in Page.

SB_THUMBPOSITION

Sets Position to the value in the Pos member in Message.

SB_THUMBTRACK

Sets Position to the value in the Pos member in Message when Tracking is enabled. No actions are performed when Tracking is set to False.

SB_TOP

Sets Position to 0 (zero).

SB_BOTTOM

Sets Position to the value in the Range property.

No actions are performed in the method if Message has any other value in its ScrollCode member. No actions are performed in the method at design-time.

ScrollHandler ensures the new value for the Position property is in the range 0..Range. Calls InvalidateScrollInfo to force scroll bar information to be re-initialized. Calls SetPosition to apply the new value for the Position property and scrolls the associated TScrollingWinControl accordingly. Sets the Result member in Message to 1 to indicate the control message was handled in the method.

ScrollHandler is called when the WMHScroll or WMVScroll methods in the associated TScrollingWinControl instance are used to handle scroll messages.

See also