problem in getting ID of MFC DialogBox

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C++

MFC

I created a dialog box in MFC using ID = IDD_DIALOG1

Then i created a simple C++ class named myClassX.

in the constructor myClassX()

when i am trying to use the name of IDD_DIALOG1, its not displaying in intellisense.

in constructor, i used the code as:-

Other IDD_.... names are there.

might be an intellisense error..

But its even not compiling..

myClassX::myClassX()
{
    Create(IDD_DIALOG1, GetDesktopWindow());
}

Its showing error "Identifier 'IDD_DIALOG1' is undefined.."

Where's could be the problem?