录制状态

要仅记录对象状态的一部分，请指定参数，然后使用函数（或其他函数）将相关信息保存在撤消文件中。kFalseautoUndoundoFiler::writeItem()write xxx ()

函数是修改函数的典型例子。因为指定，类承担记录对象状态的相关部分的责任。首先，修改函数必须记录类描述符对象，以便派生类可以检查并让此类在必要时处理其部分撤消数据。setNumSides()AsdkPolyassertWriteEnabled()kFalseautoUndo

undoFiler()->writeAddress(AsdkPoly::desc());

然后修改函数需要指示操作的类型，然后是数据。在此示例中，操作的类型是，数据是。kSetNumSidesmNumSides

Acad::ErrorStatus  
AsdkPoly::setNumSides(int numSides)    
{
    assertWriteEnabled(Adesk::kFalse, Adesk::kTrue);
    if (numSides<3)
        return Acad::eInvalidInput;
    if (mNumSides == numSides)
        return Acad::eOk;
    // There are situations under which AutoCAD doesn't
    // want to do undo recording, so it won't create an
    // undo filer. Check for the existence of the filer
    // before starting to write into it.
    //
    AcDbDwgFiler *pFiler = NULL;
    if ((pFiler = undoFiler()) != NULL) {
        undoFiler()->writeAddress(AsdkPoly::desc());
        undoFiler()->writeItem((Adesk::Int16)kSetNumSides);
        undoFiler()->writeItem((Adesk::Int32)mNumSides);
    }
    mNumSides = numSides; 
    return Acad::eOk;
}

一旦对象执行了记录其完整状态的自动撤消操作，就会忽略其他自动撤消请求。