delphi – 带有RTTI TRttiMethod.Invoke,stdcall和const参数的Bu

obj := TClassRecordTest.Create;
    try
      b.a := 10; b.b := 100;

      a.a := 1;  a.b := 2;
      writeln('b.a='+IntToStr(b.a)+' b.b='+IntToStr(b.b));
      writeln;
      writeln('call test1');
      writeln('a.a='+IntToStr(a.a)+' a.b='+IntToStr(a.b));
      r := VToRec(RTTICall(obj,'Test1',@a,@b));
      writeln('test1 r.a='+IntToStr(r.a)+' r.b='+IntToStr(r.b));

      a.a := 2;  a.b := 3;
      writeln('call test2');
      writeln('a.a='+IntToStr(a.a)+' a.b='+IntToStr(a.b));
      r := VToRec(RTTICall(obj,'Test2',@b));
      writeln('test3 r.a='+IntToStr(r.a)+' r.b='+IntToStr(r.b));

      a.a := 3;  a.b := 4;
      writeln('call test3');
      writeln('a.a='+IntToStr(a.a)+' a.b='+IntToStr(a.b));
      r := VToRec(RTTICall(obj,'Test3',@b));
      writeln('test3 r.a='+IntToStr(r.a)+' r.b='+IntToStr(r.b));

      a.a := 4;  a.b := 5;
      writeln('call test4');
      writeln('a.a='+IntToStr(a.a)+' a.b='+IntToStr(a.b));
      r := VToRec(RTTICall(obj,'Test4',@b));
      writeln('test4 r.a='+IntToStr(r.a)+' r.b='+IntToStr(r.b));

    finally
      obj.Destroy;
    end;

RTTICall它是：

function RTTICall(aObj: TObject; MethodName: string; a,b: pointer): TValue;
var
  RttiContext: TRttiContext;
  ClassType: TRttiType;
  Methods: TMethodList;
  Method: TRttiMethod;
  Params: TParamList;
  Args: TArgList;
begin
  RttiContext := TRttiContext.Create;
  try
    ClassType := FindFirstClassTypeByName(RttiContext,aObj.ClassName);
    if ClassType <> nil then
    begin
      Methods := ClassType.GetDeclaredMethods;
      for Method in Methods
      do begin
        if SameText(Method.Name,MethodName) then
        begin
          Params := Method.GetParameters;
          SetLength(Args,Length(Params));
          TValue.Make(nil,Params[0].ParamType.Handle,Args[0]);
          move(a^,Args[0].GetReferenceToRawData^,Params[0].ParamType.TypeSize);
          TValue.Make(nil,Params[1].ParamType.Handle,Args[1]);
          move(b^,Args[1].GetReferenceToRawData^,Params[1].ParamType.TypeSize);

          Result := Method.Invoke(TObject(aObj),Args);
          exit;
        end;
      end;
    end;
  finally
//    FreeAndNil(aObj);
  end;
end;

和功能TestN：

function TClassRecordTest.Test1(a,b: TRecordTest): TRecordTest;
begin
  result.a := a.a+b.a;
  result.b := a.b+b.b;
end;

function TClassRecordTest.Test2(var a,b: TRecordTest): TRecordTest;
begin
  result.a := a.a+b.a;
  result.b := a.b+b.b;
end;

function TClassRecordTest.Test3(const a,b: TRecordTest): TRecordTest;
begin
  result.a := a.a+b.a;
  result.b := a.b+b.b;
end;

function TClassRecordTest.Test4(const  a,b: TRecordTest): TRecordTest;
begin
  result.a := a.a+b.a;
  result.b := a.b+b.b;
end;

结果是：

>Project7.exe
b.a=10 b.b=100

call test1
a.a=1 a.b=2
test1 r.a=11 r.b=102
call test2
a.a=2 a.b=3
test3 r.a=12 r.b=103
call test3
a.a=3 a.b=4
test3 r.a=13 r.b=104
call test4
a.a=4 a.b=5
EAccessViolation: Access violation at address 0047A65A in module 'Project7.exe'. Read of address 00000004

仅当用作参数const和stdcall时才会发生此错误.

如果我改变Test3和Test4：

function TClassRecordTest.Test3(const a,b: TRecordTest): TRecordTest;
begin
  writeLn('@a='+IntToStr(integer(@a))+' @b='+IntToStr(integer(@a)));
  result.a := a.a+b.a;
  result.b := a.b+b.b;
end;

function TClassRecordTest.Test4(const  a,b: TRecordTest): TRecordTest;
begin
  writeLn('@a='+IntToStr(integer(@a))+' @b='+IntToStr(integer(@a)));
  result.a := a.a+b.a;
  result.b := a.b+b.b;
end;

结果是：

>Project7.exe
b.a=10 b.b=100

call test1
a.a=1 a.b=2
test1 r.a=11 r.b=102
call test2
a.a=2 a.b=3
test3 r.a=12 r.b=103
call test3
a.a=3 a.b=4
@a=31301448 @b=31301448
test3 r.a=13 r.b=104
call test4
a.a=4 a.b=5
@a=4 @b=4
EAccessViolation: Access violation at address 0047A76C in module 'Project7.exe'. Read of address 00000004

事实证明,TRttiMethod.Invoke const按值传递,尽管有必要传递地址