TControlScrollBar.ScrollHandler procedure
Handler for scroll bar movement messages.
Declaration
procedure ScrollHandler(var Message: TLMScroll)Arguments
Message | Control message examined in the method. |
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
An experiment, built from development snapshots. Not the official Free Pascal or Lazarus documentation.