无法从其他类调用方法？

我有一个头文件是方法，第二个c++文件是实现这些方法的地方，第三个主文件是我想从第二个c++文件调用方法的地方。

我已经用注释说明了哪些行出现了错误。

Root.h file (just methods):

class Root
{
    //File
    public: void NewFile(void);
    public: void OpenFile(void);
    public: void SaveFile(void);
    public: void SaveAsFile(void);
    public: void Print(void);
    public: void Exit(void);
    //Edit
    public: void Undo(void);
    public: void Redo(void);
    public: void Cut(void);
    public: void Copy(void);
    public: void Paste(void);
    public: void SelectAll(void);
    //Tools
    public: void Options(void);
    //Help
    public: void About(void);
};

Root.cpp

#include "stdafx.h"
#include "Root.h"
using namespace System::Windows::Forms;
using namespace System::IO;
class Nroot : public Root
{
    void OpenFile()
    {
        OpenFileDialog^ opf = gcnew OpenFileDialog();
        opf->InitialDirectory = "C://";
        opf->Filter = "Text Files|*.txt";
        if(opf->ShowDialog() == DialogResult::OK) //here is first error C3063: operator '==':  all operands must have the same enumeration type 
        {
            StreamReader^ sr = gcnew StreamReader(opf->FileName);
            MessageBox::Show(sr->ReadToEnd());
        }
    }
};

主文件 (just event)

private: System::Void openToolStripMenuItem_Click(System::Object^  sender, System::EventArgs^  e) {
    Nroot nr;
    nr.OpenFile; //here is second error C3867: 'WindowsFormsApplication2::Nroot::OpenFile': function call missing argument list; use '&WindowsFormsApplication2::Nroot::OpenFile' to create a pointer to member c:userssrdjandocumentsvisual studio 2012projectswindowsformsapplication2windowsformsapplication2Form1.h 325
}