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How to Move ListBox Items with the Mouse (Drag and Drop)

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How to Move ListBox Items with the Mouse (Drag and Drop)

The TListBox Delphi component displays a collection of items in a scrollable list. Delphi makes it easy to program dragging and dropping into your applications.

Here's how to allow a user to rearrange (change item's position) the items of a ListBox using drag and drop:

  1. Drop a TListBox (named ListBox1) on a form
  2. Add several strings using the Items property
  3. Set ListBox1's DragMode to dmAutomatic (in Form's OnCreate or using Object Inspector at design-time).
  4. Handle LisBox-es MouseDown, DragOver and DragDrop events
 var // form level
    StartingPoint : TPoint;
 
 implementation
 
 ...
 
 procedure TForm1.FormCreate(Sender: TObject) ;
 begin
    ListBox1.DragMode := dmAutomatic;
 end;
 
 procedure TForm1.ListBox1DragDrop(Sender, Source: TObject; X, Y: Integer) ;
 var
    DropPosition, StartPosition: Integer;
    DropPoint: TPoint;
 begin
    DropPoint.X := X;
    DropPoint.Y := Y;
    with Source as TListBox do
    begin
      StartPosition := ItemAtPos(StartingPoint,True) ;
      DropPosition := ItemAtPos(DropPoint,True) ;
 
      Items.Move(StartPosition, DropPosition) ;
    end;
 end;
 
 procedure TForm1.ListBox1DragOver(Sender, Source: TObject; X, Y: Integer; State: TDragState; var Accept: Boolean) ;
 begin
    Accept := Source = ListBox1;
 end;
 
 procedure TForm1.ListBox1MouseDown(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer) ;
 begin
    StartingPoint.X := X;
    StartingPoint.Y := Y;
 end; 

Delphi tips navigator:
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