从Excel工作簿删除工作表时出错

Question

I need to delete some sheets from an Excel workbook in C#.

But, my code does not work.

    // **aDeleteList** hold the sheets that need to be deleted from the workbook wbk
    static void delete_sht(ref MsExcel.Workbook wbk, List<string> aDeleteList)
    {
        MsExcel.Sheets my_st = wbk.Sheets;
        foreach (MsExcel.Worksheet s in my_st)
        {
            if (aDeleteList.Contains(s.Name))
                s.Delete();
            int t1 = my_st.Count;
            int t = wbk.Sheets.Count;
        }
    }

The values of t and t1 do not change no matter

          s.Delete()

has been executed.

Any help would be appreciated.

Answer 1

Removing while iterating can be a bit tricky. You are iterating through s and trying to delete s also. Something like this should work a bit better

static void delete_sht(ref MsExcel.Workbook wbk, List<string> aDeleteList)
    {
        MsExcel.Sheets my_st = wbk.Sheets;

        for (int i = my_st.Count - 1; i >= 0; --i)
            if (aDeleteList.Contains(my_st[i].Name))
                my_st.RemoveAt(i);
    }

Answer 2

You cannot delete from an underlying collection while iterating in foreach . Use a for loop instead.
From MSDN :

The foreach statement repeats a group of embedded statements for each element in an array or an object collection that implements the System.Collections.IEnumerable or System.Collections.Generic.IEnumerable interface. The foreach statement is used to iterate through the collection to get the information that you want, but can not be used to add or remove items from the source collection to avoid unpredictable side effects . If you need to add or remove items from the source collection, use a for loop.