ControlsTDragState (Delphi)

Description

This code is a TPanel's OnDragOver event handler that will not allow a label control to be dropped on the panel and stops the dragging of the label as soon as you drag the label onto the panel.

Note: Set the label's DragMode property to dmAutomatic.

Code

type
  TForm1 = class(TForm)
    Panel1: TPanel;
    Label1: TLabel;
    procedure Panel1DragOver(Sender, Source: TObject; X, Y: Integer;
      State: TDragState; var Accept: Boolean);
    procedure FormDragOver(Sender, Source: TObject; X, Y: Integer;
      State: TDragState; var Accept: Boolean);
    procedure FormDragDrop(Sender, Source: TObject; X, Y: Integer);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
 
var
  Form1: TForm1;
 
implementation
 
{$R *.dfm}
 
procedure TForm1.FormDragDrop(Sender, Source: TObject; X, Y: Integer);
begin
  TLabel(Source).Left := X;
  TLabel(Source).Top := Y;
end;
 
procedure TForm1.FormDragOver(Sender, Source: TObject; X, Y: Integer;
  State: TDragState; var Accept: Boolean);
begin
  Accept := Source is TLabel;
end;
 
procedure TForm1.Panel1DragOver(Sender, Source: TObject; X, Y: Integer;
  State: TDragState; var Accept: Boolean);
begin
  Accept := False;
  if (Source is TLabel) and (State = dsDragEnter) then
    (Source as TLabel).EndDrag(False);
end;

Uses

• Vcl.Controls.TDragState ( fr | de | ja )
• Vcl.Controls.TControl.OnDragDrop ( fr | de | ja )
• Vcl.Controls.TControl.OnDragOver ( fr | de | ja )

See Also

• Implementing Drag and Drop in Controls