Unit[]
Hierarchy[]
System.TObject < Classes.TPersistent < Classes.TComponent < Controls.TControl < Controls.TWinControl
Description[]
This is essentially a wrapper for the standard windows scroll bar
Technical Comments[]
(Known issues / Documentation clarifications / Things to be aware of)
Examples[]
Typical usage:[]
to add a scroll bar to the right of your own text box class
cActiveText = class( TCustomControl ) // ie a TWinControl descendant
public
constructor Create( sender : TObject; form : TForm );
private
mScroller : TScrollBar;
procedure ATScrollerScroll(Sender: TObject; ScrollCode: TScrollCode; var ScrollPos: Integer);
in the create method
constructor cActiveText.Create( sender : TObject; form : TForm );
begin
inherited Create( form );
....
Top := 100; // set your canvas size
Left := 0;
Width := mForm.ClientWidth;
Height := mForm.ClientHeight - 100;
mScroller := TScrollBar.Create( form ); // create here ( not on the form at design time )
mScroller.Parent := self;
mScroller.Kind := sbVertical;
mScroller.Align := alRight;
mScroller.OnScroll := ATScrollerScroll; // handle the scroll event
end;
procedure cActiveText.ATScrollerScroll(Sender: TObject; ScrollCode: TScrollCode;
var ScrollPos: Integer);
begin
Invalidate;
end;
when adding text to be displayed
function cActiveText.NewLine() : integer;
begin
mScroller.Hide;
mScroller.PageSize := 1; // to avoid unpleasantness
Inc( mNLines ); // line count
mScroller.SetParams( 1, 1, mNLInes ); // set scroller position, min and max
Invalidate;
end;
when painting
procedure cActiveText.Paint;
dyText := Canvas.TextHeight( '_A' );
dyLine := dyText + 4;
lines := Height div dyLine; // calculate displayable lines
if Height <= mNLines * dyLine then begin // too many lines to fit on the screen
mScroller.LargeChange := lines; // set page up/down to number of screen lines
mScroller.PageSize := lines; // and the scroller tab
FirstLine := mScroller.Position;
mScroller.Show;
end
else mScroller.Hide; // if it fits hide the scrollbar
TextOut( Lines[ FirstLine ) // paint from
See Also[]
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