1.如果把DragMode设置成dmAutoMatic 自动就会有拖拽效果。

2.如果把DragMode设置成dmManual，则需要调用BeginDrag才起作用，这个函数有两个参数(Immediate: Boolean; Threshold: Integer)

  Immediate = true 则拖拽操作会立刻开始，鼠标变成dragCursor类型，Immediate = false 当达到Threshold设定的值时，会产生拖拽操作。

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    Edit1: TEdit;
    Label1: TLabel;
    ListBox1: TListBox;
    procedure Button1Click(Sender: TObject);
    procedure Edit1MouseDown(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
    procedure Label1MouseDown(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
    procedure ListBox1DragOver(Sender, Source: TObject; X, Y: Integer;
      State: TDragState; var Accept: Boolean);
    procedure ListBox1DragDrop(Sender, Source: TObject; X, Y: Integer);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

  TF1 = class(TForm1)

  end;

var
  Form1: TForm1;

implementation

uses Unit2, Unit3;

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
var
  F2: TF1;
  F3: TForm1;
begin
  f3 := f2;
end;

procedure TForm1.Edit1MouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  if Button = mbleft then
    Edit1.BeginDrag(False, 10);
end;

procedure TForm1.Label1MouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
    if Button = mbleft then
    Label1.BeginDrag(False, 10);
end;

procedure TForm1.ListBox1DragOver(Sender, Source: TObject; X, Y: Integer;
  State: TDragState; var Accept: Boolean);
begin
  if (Source = Label1) or (Source = Edit1) then
    Accept := True;
end;

procedure TForm1.ListBox1DragDrop(Sender, Source: TObject; X, Y: Integer);
begin
  if (Sender = ListBox1) and (Source = Label1) then
  begin
    ListBox1.Items.Add(TLabel(Source).Caption);
  end;

  if (Sender = ListBox1) and (Source = Edit1) then
  begin
    ListBox1.Items.Add(TEdit(Source).Text + ' haha ');
  end;
end;

end.