文章来源：
http://anony3721.blog.163.com/blog/static/5119742010866050589/
一.主单元
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 type
11 TFrmMain = class(TForm)
12 Edit1: TEdit;
13 Button1: TButton;
14 Image1: TImage;
15 procedure Button1Click(Sender: TObject);
16 private
17 { Private declarations }
18 procedure Test(str:string); {定义一个用于回调的过程}
19 public
20 { Public declarations }
21 end;
22
23 var
24 FrmMain: TFrmMain;
25
26 implementation
27 {引用子窗体单元}
28 uses UnChild;
29 {$R *.dfm}
30
31 procedure TFrmMain.Button1Click(Sender: TObject);
32 begin
33 {调用Unit2的接口方法}
34 CallUnit2(test);
35 end;
36
37 {回调过程的实现部分}
38 procedure TFrmMain.test(str: string);
39 begin
40 {将str值副给Edit1}
41 Edit1.Text:=str;
42 end;
43
44 end.
二.子单元
1 unit UnChild;
2
3 interface
4
5 uses
6 Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
7 Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls;
8
9 type
10 TFuncCallBack = procedure(str:string) of object;
11 TFrmChild = class(TForm)
12 Edit1: TEdit;
13 Button1: TButton;
14 procedure Button1Click(Sender: TObject);
15 private
16 public
17 {定义一个回调函数类型的变量}
18 aFuncCallBack:TFuncCallBack;
19 end;
20 {提供给Unit1调用的接口方法,注意里面的参数的类型}
21 procedure CallUnit2(FuncCallBack:TFuncCallBack);
22 var
23 FrmChild: TFrmChild;
24
25 implementation
26
27 {$R *.dfm}
28 {接口方法的实现部分}
29 procedure CallUnit2(FuncCallBack:TFuncCallBack);
30 begin
31 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 begin
39 {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.