Title: tListBox Tricks
Question: How can you add a horizontal Scrollbar to a Listbox ?
How can you move items in a ListBox with Drag and Drop
(which scrolls if you reach the top or the bottom) ?
Answer:
* How can you add a horizontal Scrollbar to a Listbox ?
SendMessage(ListBox.Handle, LB_SETHORIZONTALEXTENT, MaxWidth, 0);
or simply
ListBox.ScrollWidth := MaxWidth;
* How can you determine the Listbox index of the topmost entry or item,
which is displayed at the top of the Listbox ?
TopIndex := SendMessage(ListBox.Handle, LB_GETTOPINDEX, 0, 0);
or simply
ListBox.TopIndex;
* How can you move items in a ListBox with Drag and Drop ?
1. set DragMode on dmAutomatic
2. implement OnDragOver and OnDragDrop Events
procedure TForm1.ListBox1DragOver(Sender, Source: TObject; X, Y: Integer;
State: TDragState; var Accept: Boolean);
begin
Accept := Sender is TListBox;
end;
procedure TForm1.ListBox1DragDrop(Sender, Source: TObject; X, Y: Integer);
var Box : tListBox;
s : string;
TargetIndex : integer;
begin
// delete selected item
// and insert at new position
// determined by ItemAtPos(..)
Box:=TListBox(Source);
s:=Box.Items[Box.ItemIndex];
Box.Items.Delete(Box.ItemIndex);
TargetIndex:=Box.ItemAtPos(Point(x,y),true);
Box.Items.Insert(TargetIndex,s);
Box.ItemIndex:=TargetIndex;
end;
* How can you move items in a ListBox with Drag and Drop,
which scrolls if you reach the top or the bottom ?
procedure TForm1.ListBox1Click(Sender: TObject);
begin
// save source ItemIndex
SourceIndex:=(Sender as TListBox).ItemIndex;
end;
procedure TForm1.ListBox1DragOver(Sender, Source: TObject; X, Y: Integer;
State: TDragState; var Accept: Boolean);
var
TargetPos : integer;
Box : tListBox;
r : tRect;
begin
Box := Sender as TListBox;
TargetPos := Box.ItemAtPos(Point(x,y),True);
Box.ItemIndex := TargetPos;
r:=Box.ItemRect(TargetPos);
if r.top begin
if TargetPos 0 then
Box.ItemIndex:=TargetPos-1;
end else
if r.bottom (Box.Height-Box.ItemHeight) then
begin
if TargetPos Box.ItemIndex:=Box.ItemIndex+1;
end;
if (TargetPos = -1)
then Accept := False
else Accept := True;
end;
procedure TForm1.ListBox1DragDrop(Sender, Source: TObject; X, Y: Integer);
var Box : tListBox;
s : string;
TargetIndex : integer;
begin
// delete selected item
// and insert at new position
// determined by ItemAtPos(..)
Box:=TListBox(Source);
s:=Box.Items[SourceIndex];
Box.Items.Delete(SourceIndex);
TargetIndex:=Box.ItemAtPos(Point(x,y),true);
Box.Items.Insert(TargetIndex,s);
Box.ItemIndex:=TargetIndex;
end;