Return #N/A if a heavy function is called from a dialog box.

XllConnector/Invoke.cpp

@@ -79,4 +79,38 @@ ExcelVariant ExcelCall(int xlfn, const T&... args)
 	Excel12(xlFree, 0, 1, &result);
 	return vResult;
 }
-#endif
+#endif
+
+namespace XLL_NAMESPACE
+{
+	// How to: Call XLL Functions from the Function Wizard or Replace Dialog Boxes
+	// https://msdn.microsoft.com/EN-US/library/office/bb687909.aspx
+
+	static BOOL CALLBACK IsDialogBoxOpen_Callback(HWND hwnd, LPARAM lParam)
+	{
+		bool *pFound = (bool*)lParam;
+
+		DWORD dwProcessId = 0;
+		GetWindowThreadProcessId(hwnd, &dwProcessId);
+		if (dwProcessId == GetCurrentProcessId())
+		{
+			WCHAR szClassName[100];
+			if (GetClassNameW(hwnd, szClassName, ARRAYSIZE(szClassName)))
+			{
+				if (_wcsnicmp(szClassName, L"bosa_sdm_XL", 11) == 0)
+				{
+					*pFound = true;
+					return FALSE; // stop iterating
+				}
+			}
+		}
+		return TRUE; // keep iterating
+	}
+
+	bool IsDialogBoxOpen()
+	{
+		bool bFoundDialog = false;
+		EnumWindows(IsDialogBoxOpen_Callback, (LPARAM)&bFoundDialog);
+		return bFoundDialog;
+	}
+}

XllConnector/Invoke.h

@@ -22,4 +22,8 @@ namespace XLL_NAMESPACE
 		explicit ExcelException(int errorCode);
 		const char* what() const override { return m_errorMessage; }
 	};
+
+	// Returns true if the Function Wizard or Replace dialog box is
+	// open in the current Excel session.
+	bool IsDialogBoxOpen();
 }

XllConnector/Wrapper.h

@@ -7,6 +7,7 @@
 #include "FunctionInfo.h"
 #include "Conversion.h"
 #include "Marshal.h"
+#include "Invoke.h"
 
 //
 // strip_cc, strip_cc_t
@@ -179,6 +180,11 @@ namespace XLL_NAMESPACE
 		{
 			try
 			{
+				if (IsHeavy && IsDialogBoxOpen())
+				{
+					return const_cast<LPXLOPER12>(&Constants::ErrNA);
+				}
+
 				LPXLOPER12 pvRetVal = AllocateReturnValue(IsThreadSafe);
 				HRESULT hr = CreateValue(pvRetVal,
 					func(ArgumentMarshaler<TArgs>::Marshal(args)...));

XllExamples/ArithmeticExample.cpp

@@ -18,7 +18,7 @@ namespace custom_ns
 	}
 }
 
-EXPORT_XLL_FUNCTION_AS(custom_ns::GetCircleArea, GetCircleArea);
+EXPORT_XLL_FUNCTION_AS(custom_ns::GetCircleArea, GetCircleArea, XLL_LIGHT);
 
 namespace
 {