I have an AddIn which I want to invoke through Excel interop from a C# winforms application.
I can\'t get the addin etc. to load unless I uninstall and resinstall it
After a while I found the answer hidden in strange places in the MS help: and this blog post.
That isn't all the info you need though. Things to note: you must have at least one workbook open or otherwise Excel barfs. Here's some rudementry code to get started:
var excel = new Application();
var workbook = excel.workbooks.Add(Type.Missing);
excel.RegisterXLL(pathToXll);
excel.ShowExcel();
If you want you can close the temporary workbook (if you've run some macros etc.) and remember to tidy everything up with plenty of calls to Marshal.ReleaseComObject!
It seems that you have to get the correct Excel process to work with. Use this class to open the Excel document:
class ExcelInteropService
{
private const string EXCEL_CLASS_NAME = "EXCEL7";
private const uint DW_OBJECTID = 0xFFFFFFF0;
private static Guid rrid = new Guid("{00020400-0000-0000-C000-000000000046}");
public delegate bool EnumChildCallback(int hwnd, ref int lParam);
[DllImport("Oleacc.dll")]
public static extern int AccessibleObjectFromWindow(int hwnd, uint dwObjectID, byte[] riid, ref Window ptr);
[DllImport("User32.dll")]
public static extern bool EnumChildWindows(int hWndParent, EnumChildCallback lpEnumFunc, ref int lParam);
[DllImport("User32.dll")]
public static extern int GetClassName(int hWnd, StringBuilder lpClassName, int nMaxCount);
public static Application GetExcelInterop(int? processId = null)
{
var p = processId.HasValue ? Process.GetProcessById(processId.Value) : Process.Start("excel.exe");
try
{
Thread.Sleep(5000);
return new ExcelInteropService().SearchExcelInterop(p);
}
catch (Exception)
{
Debug.Assert(p != null, "p != null");
return GetExcelInterop(p.Id);
}
}
private bool EnumChildFunc(int hwndChild, ref int lParam)
{
var buf = new StringBuilder(128);
GetClassName(hwndChild, buf, 128);
if (buf.ToString() == EXCEL_CLASS_NAME) { lParam = hwndChild; return false; }
return true;
}
private Application SearchExcelInterop(Process p)
{
Window ptr = null;
int hwnd = 0;
int hWndParent = (int)p.MainWindowHandle;
if (hWndParent == 0) throw new Exception();
EnumChildWindows(hWndParent, EnumChildFunc, ref hwnd);
if (hwnd == 0) throw new Exception();
int hr = AccessibleObjectFromWindow(hwnd, DW_OBJECTID, rrid.ToByteArray(), ref ptr);
if (hr < 0) throw new Exception();
return ptr.Application;
}
}
Use the class in your application like this:
static void Main(string[] args)
{
Microsoft.Office.Interop.Excel.Application oExcel = ExcelInteropService.GetExcelInterop();
foreach (AddIn addIn in oExcel.AddIns)
{
addIn.Installed = true;
}
}