Delphi RTTI问题:GetPropInfo在{$ METHODINFO ON}时返回nil？

Question

即使使用正确的{$ METHODINFO}指令声明给定的类,GetPropInfo是否有可能返回nil.

  type 
  ... 
  ...
    {$METHODINFO ON}
    TMyClass = class
    private
      fField: integer;
    published
      property Field: integer read fField write fField;
    end;
    {$METHODINFO OFF}
  ...
  ...
  procedure TestRTTI;
  begin
    assert(assigned(GetPropInfo(TMyClass, 'Field')), 'WTF! No RTTI found!');
  end;

Answer 1

疑难杂症!似乎这个问题隐藏在我忽略的前瞻声明中.不知道偷偷摸摸的功能.

似乎编译器只考虑类的第一个声明来生成RTTI,所以如果你有这样的前向声明......

  type 
    TMyClass = class;   
    ...    
    ...
    {$METHODINFO ON}
    TMyClass = class
    private
      fField: integer;
    published
      property Field: integer read fField write fField;
    end;
    {$METHODINFO OFF}   
    ...   
    ...   
    procedure TestRTTI;   
    begin
      assert(assigned(GetPropInfo(TMyClass, 'Field')), 'WTF! No RTTI found!');   
    end;

...你会得到断言错误.因此,为了使RTTI正确,需要为正向声明启用{$ METHODINFO}指令,如此处所示....

  type 
    {$METHODINFO ON}
    TMyClass = class;   
    {$METHODINFO OFF}   
    ...    
    ...
    TMyClass = class
    private
      fField: integer;
    published
      property Field: integer read fField write fField;
    end;
    ...