Public Overridable Sub PreviewIsFullScreen( _
   ByVal _bsChannelID As String, _
   ByRef _pbFullScreen As Integer, _
   ByRef _pnDisplay As Integer _
) 

public virtual void PreviewIsFullScreen( 
   string _bsChannelID,
   ref int _pbFullScreen,
   ref int _pnDisplay
)

public procedure PreviewIsFullScreen( 
    _bsChannelID: String;
   var  _pbFullScreen: Integer;
   var  _pnDisplay: Integer
); virtual; 

public: virtual void PreviewIsFullScreen( 
   BSTR* _bsChannelID,
   ref int _pbFullScreen,
   ref int _pnDisplay
) 

Parameters

_bsChannelID

channel ID. By default use empty string

_pbFullScreen

0 means that full screen is disabled, 1 means that it is enabled

_pnDisplay

number of display

Here is example of how to check whether preview is in full screen mode:

int isFullScreen = 0;
int nDisplay = 0;
m_objPreview.PreviewIsFullScreen("", ref isFullScreen, ref nDisplay);

Reference

MFPreviewClass Class
MFPreviewClass Members