Here's a class to add "multi-select" to some simple grid items. It lets you display blank values when the data you are displaying have conflicting values.

class IMultiValue { public:  virtual bool IsMultiValue() = 0; }; template <class GridItemClass> class MultiSelect : public GridItemClass, public IMultiValue { public:  MultiSelect(CString x):GridItemClass(x)  {   CXTPPropertyGridItem::SetValue("");  }  virtual void SetValue(CString strValue)  {   if (strValue.IsEmpty())    CXTPPropertyGridItem::SetValue(strValue);   else    __super::SetValue(strValue);  }  virtual bool IsMultiValue()  {   return GetValue().IsEmpty();  } };

Usage:

CXTPPropertyGridItemBool* b = new MultiSelect<CXTPPropertyGridItemBool>(_T("BoolTest")); myCategory->AddChildItem(b);

This class could be extended to have "addValue" and "resetValue" functions...

Is there a better way to do this? Has anybody else tried?