访问冲突在XE2中强制转换IDispatch

Question

我们正在使用一些旧代码(由Binh Ly创建的ComLib.pas),因此我们可以在(OleVariant)对象上使用枚举接口:

type
  TDispNewEnum = dispinterface
    ['{97079E31-6957-11D2-9154-0000B4552A26}'] // dummy
    property _NewEnum: IUnknown readonly dispid -4; // DISPID_NEWENUM
    function _NewEnumFunc: IUnknown; dispid -4; // DISPID_NEWENUM
  end;

procedure TEnumVariant.AttachUnknown (const Unk: IUnknown);
var
  pDisp: IDispatch;
  _NewEnumPropFailed: boolean;
  Unknown: IUnknown;
begin
  Detach;
  Unknown := Unk;
  { extract IEnumVariant }
  if (Unknown <> nil) then
  begin
    { try IEnumVariant }
    if not (Succeeded (Unknown.QueryInterface (IEnumVariant, FEnumVariant))) then
    begin
      FEnumVariant := nil;  // safety!

      { test _NewEnum prop and _NewEnum func }
      if (Succeeded (Unknown.QueryInterface (IDispatch, pDisp))) then
      begin
        _NewEnumPropFailed := False;
        try
          //property _NewEnum
          Unknown:=TDispNewEnum(pDisp)._NewEnum; // <---- RAISES EXCEPTION -----
          if not (Succeeded(Unknown.QueryInterface(IEnumVariant, FEnumVariant))) then
            FEnumVariant := nil;  // safety!
        except
          _NewEnumPropFailed := True;
        end;  { except }

此代码适用于Delphi 2010和2007,但不适用于XE2.在上面标记的行上(注释"RAISES EXCEPTION"),我们得到一个例外:

项目x.exe引发了异常类$ C0000005,消息"0xbaadf00d访问冲突:读取地址0xbaadf00d".

传入的对象确实具有TDispNewEnum接口,因此不应引发任何异常(与Delphi 2010和2007的情况一样).

建议？谢谢.

Answer 1

该0xbaadf00d内存地址是一个伪内存地址,意为"坏菜"(看六字符).当您要求无效的接口或调用时,通常由代码使用.

如果将行更改为:

pDisp: TDispNewEnum;
...
if (Succeeded (Unknown.QueryInterface (IDispatch, pDisp))) then
begin
   _NewEnumPropFailed := False;
   try
     //property _NewEnum
     Unknown:= pDisp._NewEnum; 
...

这对我来说更有意义.

我注意到 XE2接口绑定中有一些未记录的更改.也许以前使用强制类型转换(TDispNewEnum(pDisp))的代码不再起作用了.