Variable become null after selection of CheckBox from GridView on RowCommand

Dear Sir,

I have facing a problem in asp.net.

i have define some variable in rowcommand of gridview but when ever i click any button or click checkbox of gridview or select any droopdown all variable become for 0 number and null for string. i can not use in further function.

please help me sir value should remain same as define during row command. all code is under updatepanel 

============================ My code ================================ 

protected void GvServiceSchedule_RowCommand(object sender, GridViewCommandEventArgs e)
{
    ServiceTypeCode = "";
    ServiceTypeDescription = "";
    ServiceTypeCode = "";
    ServiceTypeKM = 0;
    ServiceTypeNextServiceKm = 0;
    ServiceTypeChargeTo = "";
    ServiceTypeFRT = "";
    ServiceTypeTu = 0;
    ServiceTypePaid = "";
    ServiceTypeNextDays = 0;
    ServiceTypeSalePrice = 0;
    ServiceTypeCostPrice = 0;

    if (e.CommandName == "DisplayServiceItemAndLabour")
    {
        int index = Int32.Parse(e.CommandArgument.ToString());
        GridViewRow row = GvServiceSchedule.Rows[index];
        ServiceTypePaid = row.Cells[2].Text;
        ServiceTypeCode = row.Cells[3].Text;
        ServiceTypeKM = int.Parse(row.Cells[4].Text);
        ServiceTypeDescription = row.Cells[5].Text;
        ServiceTypeSalePrice = Convert.ToDouble(row.Cells[6].Text);
        ServiceTypeNextDays = int.Parse(row.Cells[7].Text);
        ServiceTypeNextServiceKm = int.Parse(row.Cells[8].Text);
        ServiceTypeChargeTo = row.Cells[9].Text;
        ServiceTypeFRT = row.Cells[10].Text;
        ServiceTypeTu = int.Parse(row.Cells[11].Text);
        ServiceTypeCostPrice = Convert.ToDouble(row.Cells[12].Text);
        LoadServicePackageList();
    }
}

// End Row Command service schedule