Notifies the delegate that the window is about to open a sheet.
Original signature is '- (void)windowWillBeginSheet:(NSNotification *)notification'
Available in Mac OS X v10.1 and later.

C# | Visual Basic | Visual C++ |
public event NSWindow..::..WindowWillBeginSheetEventHandler WindowWillBeginSheet
Public Event WindowWillBeginSheet As NSWindow..::..WindowWillBeginSheetEventHandler
public: event NSWindow..::..WindowWillBeginSheetEventHandler^ WindowWillBeginSheet { void add (NSWindow..::..WindowWillBeginSheetEventHandler^ value); void remove (NSWindow..::..WindowWillBeginSheetEventHandler^ value); }

- Available in Monobjc Bridge: 10.6 (For Mac OS X 10.6 and later), 10.5 (For Mac OS X 10.5 and later)