AbstractErrorProc - 抽象错误处理的指针

unit Unit1;



interface



uses

  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,

  Dialogs, StdCtrls;



type

  {父类}

  TBase = class

    procedure proc; virtual; abstract; {抽象方法}

  end;



  {子类}

  TChild = class(TBase)

    procedure proc; override; {在子类中覆盖、实现方法}

  end;





  TForm1 = class(TForm)

    Button1: TButton;

    procedure Button1Click(Sender: TObject);

  end;



var

  Form1: TForm1;



implementation



{$R *.dfm}



{ TChild }

//方法实现

procedure TChild.proc;

begin

  ShowMessage('IsChild');

end;





//AbstractErrorProc 将要调用的过程

procedure err;

begin

  ShowMessage('Err...');

end;



procedure TForm1.Button1Click(Sender: TObject);

var

  B: TBase;

  C: TChild;

begin

  {AbstractErrorProc 是抽象错误处理的指针, 对应一个无参数的外部过程}

  AbstractErrorProc := Addr(err);



  {在子类中调用方法, Ok}

  C := TChild.Create;

  C.proc; {IsChild}

  C.Free;



  {父类通过子类实现后调用方法, Ok}

  B := TChild.Create;

  B.proc; {IsChild}

  B.Free;



  {父类自实现后调用方法, 将会调用 AbstractErrorProc 指定的错误过程; 因为父类中的方法还是抽象的}

  B := TBase.Create;

  B.proc; {Err...}

  B.Free;

end;



end.