Load Filepath Drag&Drop to ListBox

uses ShellApi

private
    { Private declarations }
    procedure WMDROPFILES(var Msg: TMessage);
    procedure LBWindowProc(var Message: TMessage);
    procedure AddFile(sFileName: string);
    
var
  Form1: TForm1;
  OldLBWindowProc: TWndMethod;
  
//

procedure TForm1.AddFile(sFileName: string);
begin
  ListBox1.Items.Add(sFilename);
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  OldLBWindowProc := ListBox1.WindowProc; // store defualt WindowProc
  ListBox1.WindowProc := LBWindowProc; // replace default WindowProc
  DragAcceptFiles(ListBox1.Handle, True); // now ListBox1 accept dropped files
end;

procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction);
begin
  ListBox1.WindowProc := OldLBWindowProc;
  DragAcceptFiles(ListBox1.Handle, False);
end;

procedure TForm1.LBWindowProc(var Message: TMessage);
begin
  if Message.Msg = WM_DROPFILES then
    WMDROPFILES(Message); // handle WM_DROPFILES message
  OldLBWindowProc(Message);
  // call default ListBox1 WindowProc method to handle all other messages
end;

procedure TForm1.WMDROPFILES(var Msg: TMessage);
var
  pcFileName: PChar;
  i, iSize, iFileCount: integer;
begin
  pcFileName := ''; // to avoid compiler warning message
  iFileCount := DragQueryFile(Msg.wParam, $FFFFFFFF, pcFileName, 255);
  for i := 0 to iFileCount - 1 do
  begin
    iSize := DragQueryFile(Msg.wParam, i, nil, 0) + 1;
    pcFileName := StrAlloc(iSize);
    DragQueryFile(Msg.wParam, i, pcFileName, iSize);
    if FileExists(pcFileName) then
      AddFile(pcFileName); // method to add each file
    StrDispose(pcFileName);
  end;
  DragFinish(Msg.wParam);
end;