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This is just an example how you can use Drag and Drop to change the order of items is a TListBox or a TCheckListBox.
First we define a global variable, this can be a property of TForm1 for example;
DraggingItemNumber : integer;
Next we define 3 procedures for the ListBox events "OnMouseDown", "OnDragDrop", "OnDragOver".
We use OnMouseDown to identify that the user clicked a mouse button (this can be left or right mouse button), where we determine if a proper item has been selected and store that item number in the global variable.
The OnDragOver event is used to make sure the item has a place to drop, on it's own control. If that's the case we gladly accept a potential drop (mouse cursor changes).
The onDragDrop even is used to "receive" the dropped item and, if everything is legit, move the dragged item to the new location.
procedure TForm1.ListBox1MouseDown(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
begin
DraggingItemNumber := ListBox1.ItemAtPos(Point(X,Y), true);
if (DraggingItemNumber>-1) and (DraggingItemNumber<ListBox1.Count) then
ListBox1.BeginDrag(true)
else
begin
ListBox1.BeginDrag(False);
DraggingItemNumber:=-1;
end;
end; procedure TForm1.ListBox1DragDrop(Sender, Source: TObject; X, Y: Integer);
var ItemUnderMouse:integer;
begin
ItemUnderMouse := ListBox1.ItemAtPos(Point(X,Y), true);
if (ItemUnderMouse>-1) and (ItemUnderMouse<ListBox1.Count) and (DraggingItemNumber>-1) then
listShares.Items.Move(DraggingItemNumber,ItemUnderMouse);
end; procedure TForm1.ListBox1DragOver(Sender, Source: TObject; X, Y: Integer; State: TDragState; var Accept: Boolean);
var ItemUnderMouse:integer;
begin
if Sender=Source then
begin
ItemUnderMouse := ListBox1.ItemAtPos(Point(X,Y), true);
Accept:=(ItemUnderMouse>-1) and (ItemUnderMouse<ListBox1.Count);
end
else
Accept:=false;
end;
Side note, to make just Clicking (selecting) an item possible:
Set DragMode:=dmAutomatic for the ListBox or CheckListBox.
