unit UnMain;interfaceuses  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Vcl.Imaging.jpeg,  Vcl.ExtCtrls;type  TFrmMain = class(TForm)    Edit1: TEdit;    Button1: TButton;    Image1: TImage;    procedure Button1Click(Sender: TObject);  private    { Private declarations }    procedure Test(str:string); {定义一个用于回调的过程}  public    { Public declarations }  end;var  FrmMain: TFrmMain;implementation{引用子窗体单元}uses UnChild;{$R *.dfm}procedure TFrmMain.Button1Click(Sender: TObject);begin  {调用Unit2的接口方法}  CallUnit2(test);end;{回调过程的实现部分}procedure TFrmMain.test(str: string);begin  {将str值副给Edit1}  Edit1.Text:=str;end;end.

unit UnChild;interfaceuses  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls;type   TFuncCallBack = procedure(str:string) of object;  TFrmChild = class(TForm)    Edit1: TEdit;    Button1: TButton;    procedure Button1Click(Sender: TObject);  private  public    {定义一个回调函数类型的变量}    aFuncCallBack:TFuncCallBack;  end;   {提供给Unit1调用的接口方法,注意里面的参数的类型}    procedure CallUnit2(FuncCallBack:TFuncCallBack);var  FrmChild: TFrmChild;implementation{$R *.dfm}{接口方法的实现部分}procedure CallUnit2(FuncCallBack:TFuncCallBack);begin  Application.CreateForm(TFrmChild,FrmChild);  {将参数赋值给FuncCallBack}  FrmChild.aFuncCallBack:=FuncCallBack;  FrmChild.ShowModal;end;procedure TFrmChild.Button1Click(Sender: TObject);begin  {当点击Form2的按钮时将Form2中的Edit的值传递给了Form1中的Edit}  {是不是很神奇？我并没有uses Unit1,但却改变了Form1中Edit的Text属性}  aFuncCallBack(Edit1.Text);  ModalResult:=mrOk;end;end.