Excel Worksheet Adding Issue C#

The Problem I am having is that each time a number from the comboBox is selected it is creating a new worksheet. I just want the variable to be added to the active sheet only, and not create a sheet each time. Any Help is greatly appreciated.

Would something like this work?

        var xl = new Excel.Application();
        xl.Visible = true;
        var wb = (Excel._Workbook)xl.Active开发者_JAVA技巧Workbook; //(xl.Workbooks.Add(Missing.Value));
        var sheet = (Excel._Worksheet)wb.ActiveSheet;

        //Generate Linear Guide Support in Solidworks
        if (comboBox1.Text == "0")
        {
            sheet.Cells[6, 4] = "0"; //Cell Location[y-axis, x-axis]
        }
         if (comboBox2.Text == "AH")
        {
            sheet.Cells[6, 5] = "AH";
        }
        if(comboBox3.Text == "2")
        {
            sheet.Cells[6, 6] = "2";
        }        

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Factor out this code and don't invoke it for every selection. You can move this so that it is executed only once.

    // Available at the class level. single instance - Singleton pattern may be employed
    // Check the correct datatype for ExcelSheet
    ExcelSheet sheet;
    void UpdateExcelSheet(int row, int col, string value)
    {
        if (sheet == null)
        {
            var xl = new Excel.Application();
            xl.Visible = true;
            var wb = (Excel._Workbook)(xl.Workbooks.Add(Missing.Value));
            sheet = (Excel._Worksheet)wb.ActiveSheet;
        }
        sheet.Cells[row, col] = value;
    }

    void OnComboSelection()
    {
        int row, col;
        string value;
        if(comboBox5.Text == "1")
        {
            row = 6; col = 6; value = "1";
        }
        if (comboBox3.Text == "2")
        {
            row = 6; col = 8; value = "2";
        }
        UpdateExcelSheet(row, col, value);
    }