unit Unit1;

interface

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

type
   //定义一个事件格式，要传参数的格式 后面必须要加上of object
   TeacherArgnyEvent = procedure(ErrorCount: Integer) of object;

type
TTeacher = class(TObject)
private
    FStudentErrorCount: Integer;
    FOnTeacherArngy: TeacherArgnyEvent; //定义一个内部事件，private里的只能在TTeacher类内部调用
    procedure SetStudentErrorCount(Value: Integer);
public
    constructor Create;
    destructor Destroy; override;
    property StudentErrorCount: Integer read FStudentErrorCount write SetStudentErrorCount ;
    property OnTeacherArngy: TeacherArgnyEvent read FOnTeacherArngy write FOnTeacherArngy ; //定义一个外部的事件，在其它的对象里面可以通过FTeacher.ONTeacherArngy这样调用。读写是通过内部的FOnTeacherArngy
end;

type
TForm1 = class(TForm)
    Button1: TButton;
    procedure FormCreate(Sender: TObject);
    procedure FormClose(Sender: TObject; var Action: TCloseAction);
    procedure Button1Click(Sender: TObject);
    procedure IfTeacherArngy(EC: Integer); //自己定义事件触发时要执行的函数，和Button控件在事件列表中双击时出来的那段代码一样，只是这里是你自己定义的，而不是DELPHI给你生成的
private
    FTeacher: TTeacher ;
public
    { Public declarations }
end;

var
Form1: TForm1;

implementation

{$R *.dfm}

{ TTeacher }

constructor TTeacher.Create;
begin
FStudentErrorCount := 0;
end;

destructor TTeacher.Destroy;
begin

inherited;
end;

procedure TTeacher.SetStudentErrorCount(Value: Integer);
begin
FStudentErrorCount := Value;
if FStudentErrorCount > 3 then    //给StudentErrorCount赋值的时候，判断是否触发FOnTeacherArngy事件
    if Assigned(FOnTeacherArngy) then   //看FOnTeacherArngy是否为空，不为空则执行该事件，如果不判断是否为空，则执行下面一句的时候可能会有错误
      FOnTeacherArngy(FStudentErrorCount);
end;

{ TForm }

procedure TForm1.FormCreate(Sender: TObject);
begin
FTeacher := TTeacher.Create ;     //创建一个TTeacher的实例
FTeacher.OnTeacherArngy := IfTeacherArngy; //把FOrm1里的IfTeacherArngy过程赋值给FTeacher的OnTeacherArngy，这样它就不为空了
end;

procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction);
begin
FTeacher.Free ;   //窗体关闭时释放
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
FTeacher.StudentErrorCount := FTeacher.StudentErrorCount + 1; //给StudentErrorCount赋值 ，我只是给他赋值，就会触发那个事件
// 有了这个类，就不用下面这一段了，给 StudentErrorCount属性赋值就能达到下面这段代码的效果。
// if FTeacher.StudentErrorCount > 3 then
//    ShowMessage('Student 错误了' + IntToStr(ec) + '次,老师生气了。');
end;

procedure TForm1.IfTeacherArngy(EC: Integer);
begin
ShowMessage('Student 错误了' + IntToStr(ec) + '次,老师生气了。'); //事件触发时的情况，和Button控件在事件列表中双击时出来的那段代码一样，只是这里是你自己定义的，而不是DELPHI给你生成的
end;

end.