Delphi XE2 RTTI broken?

问题

I recently migrated from D2010 to DXE2 and found a showstopper bug (Or feature?) in XE2 and XE3 (Tested in my friend XE3) related to RTTI generation for TBytes fields inside classes.

I found that the RTTI information for a TBytes variable inside a class is never generated.

The following code works well in D2010, but shows the message "Error" in XE2/XE3

Does anyone have any clue? This will totally break all our software data serialization implementation

To test the code please add Rtti unit to the uses declaration

type

  TMyClass = class
  public
    Field1: Integer;
    Field2: TBytes;
  end;


procedure TForm2.Button1Click(Sender: TObject);
var
  i: Integer;
  Data: TMyClass;
  Rtti: TRttiContext;
  RttiClassType: TRttiInstanceType;
begin

  Data := TMyClass.Create;
  try

    // Get the context
    Rtti := TRttiContext.Create;
    try

      // Get the type for the class
      RttiClassType := TRttiInstanceType(Rtti.GetType(Data.ClassInfo));

      // Check the fields
      for i := 0 to High(RttiClassType.GetFields) do
      begin

        // Check the field type
        if not Assigned(RttiClassType.GetFields[i].FieldType) then
          ShowMessage('Error');

      end;

    finally
      Rtti.Free;
    end;

  finally
    Data.Free;
  end;

end;

The error message will be displayed when checking for Field2 that is a TBytes becayse the FieldType is always nil!!!

Does anyone has any clue of what have changed in the RTTI from D2010 do XE2? Maybe because the TBytes type was changed from array of Byte to the generic array?

回答1:

This is a known issue that was fixed in XE3. Unfortunately, upgrading is the only way to get a fix for it; bug fixes don't usually get ported back.

EDIT: Or not. Apparently this is not actually fixed, as it still occurs in XE3. Reporting it as a new case and mentioning 103729 would probably be the best course of action.

回答2:

You can fix this error (it is actually not the same bug as the one Mason mentioned).

type
  FixTypeInfoAttribute = class(TCustomAttribute)
  public
    FTypeInfo: PPTypeInfo;
    constructor Create(TypeInfo: PTypeInfo);
  end;

procedure FixFieldType(TypeInfo: PTypeInfo);
var
  ctx: TRttiContext;
  t: TRttiType;
  f: TRttiField;
  a: TCustomAttribute;
  n: Cardinal;
begin
  t := ctx.GetType(TypeInfo);
  for f in t.GetFields do
  begin
    for a in f.GetAttributes do
    begin
      if (a is FixTypeInfoAttribute) and f.ClassNameIs('TRttiInstanceFieldEx') then
      begin
        WriteProcessMemory(GetCurrentProcess, @PFieldExEntry(f.Handle).TypeRef,
          @FixTypeInfoAttribute(a).FTypeInfo, SizeOf(Pointer), n);
      end;
    end;
  end;
end;

constructor FixTypeInfoAttribute.Create(TypeInfo: PTypeInfo);
begin
  FTypeInfo := PPTypeInfo(PByte(TypeInfo) - SizeOf(Pointer));
end;

Then you add the attribute to your class definition:

type
  TMyClass = class
  private
    Field1: Integer;
    [FixTypeInfo(TypeInfo(TBytes))]
    Field2: TBytes;
  end;

and make sure the FixFieldType routine is called:

initialization
  FixFieldType(TypeInfo(TMyClass));

Tested on XE

来源：https://stackoverflow.com/questions/12679240/delphi-xe2-rtti-broken