How do I access public attributes from other objects?

I have the following situation: The function OnNMClick (from the derived CTreeCtrl class CMyTreeCtrl) is called when I click in the dialog box. That dialog (CMyDialog) has a attribute (m_data) from type CMyData (with operation change()) that I want to access in the OnNMClick function. This is necessary to change the data in CMyDialog. What I do is this:
Code:
CMyDialog::m_data.change();
But this results in the following error:
Code:
G:\MyTreeCtrl.cpp(56) : error C2228: left of '.change' must have class/struct/union type
Any help would be highly appreciated.