1 unit UnMain; 2  3 interface 4  5 uses 6   Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics, 7   Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Vcl.Imaging.jpeg, 8   Vcl.ExtCtrls; 9 10 type11   TFrmMain = class(TForm)12     Edit1: TEdit;13     Button1: TButton;14     Image1: TImage;15     procedure Button1Click(Sender: TObject);16   private17     { Private declarations }18     procedure Test(str:string); {定义一个用于回调的过程}19   public20     { Public declarations }21   end;22 23 var24   FrmMain: TFrmMain;25 26 implementation27 {引用子窗体单元}28 uses UnChild;29 {$R *.dfm}30 31 procedure TFrmMain.Button1Click(Sender: TObject);32 begin33   {调用Unit2的接口方法}34   CallUnit2(test);35 end;36 37 {回调过程的实现部分}38 procedure TFrmMain.test(str: string);39 begin40   {将str值副给Edit1}41   Edit1.Text:=str;42 end;43 44 end.

 1 unit UnChild; 2  3 interface 4  5 uses 6   Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics, 7   Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls; 8  9 type10    TFuncCallBack = procedure(str:string) of object;11   TFrmChild = class(TForm)12     Edit1: TEdit;13     Button1: TButton;14     procedure Button1Click(Sender: TObject);15   private16   public17     {定义一个回调函数类型的变量}18     aFuncCallBack:TFuncCallBack;19   end;20    {提供给Unit1调用的接口方法,注意里面的参数的类型}21     procedure CallUnit2(FuncCallBack:TFuncCallBack);22 var23   FrmChild: TFrmChild;24 25 implementation26 27 {$R *.dfm}28 {接口方法的实现部分}29 procedure CallUnit2(FuncCallBack:TFuncCallBack);30 begin31   Application.CreateForm(TFrmChild,FrmChild);32   {将参数赋值给FuncCallBack}33   FrmChild.aFuncCallBack:=FuncCallBack;34   FrmChild.ShowModal;35 end;36 37 procedure TFrmChild.Button1Click(Sender: TObject);38 begin39   {当点击Form2的按钮时将Form2中的Edit的值传递给了Form1中的Edit}40   {是不是很神奇？我并没有uses Unit1,但却改变了Form1中Edit的Text属性}41   aFuncCallBack(Edit1.Text);42   ModalResult:=mrOk;43 end;44 45 end.