delphi回调函数

文章来源：
http://anony3721.blog.163.com/blog/static/5119742010866050589/

一.主单元

 unit UnMain;

 interface

 uses
   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.

二.子单元

 unit UnChild;

 interface

 uses
   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.