一次选择一个下拉菜单

Question

我有一个gridview，每行都有下拉列表，我想如果用户在一个下拉列表中选择值，那么他可能不会选择另一个下拉列表，但如果他选择那么它应该通过错误：

抱歉，您可以一次选择1个值

int count = 0;
    protected void ddlIsComplaint_SelectedIndexChanged(object sender, EventArgs e) //not used yet
    {
        count = count + 1;
        DropDownList ddl = (DropDownList)sender;
        GridViewRow row = (GridViewRow)ddl.NamingContainer;
        //int ID = Convert.ToInt32(row.Cells[0].Text);
        //short IsComplaint = Convert.ToInt16(ddl.SelectedValue);
        HiddenFieldIsValidDropDownValue.Value = row.Cells[0].Text;
        int RowID = Convert.ToInt16(HiddenFieldIsValidDropDownValue.Value);

        if (count >= 1) 
        {
            lblSelectionMessage.InnerText = count.ToString();
        }





}

Answer 1

               Label1.Text = "yes";
               protected void ddlIsComplaint_SelectedIndexChanged(object sender, EventArgs e) //not used yet
                {

               if(Label1.Text!="No")
                {                  
                  DropDownList ddl = (DropDownList)sender;
                  GridViewRow row = (GridViewRow)ddl.NamingContainer;
                  //int ID = Convert.ToInt32(row.Cells[0].Text);
                  //short IsComplaint = Convert.ToInt16(ddl.SelectedValue);
                  HiddenFieldIsValidDropDownValue.Value = row.Cells[0].Text;
                  int RowID = Convert.ToInt16(HiddenFieldIsValidDropDownValue.Value);

                }
              else 
               {
                   lblSelectionMessage.InnerText = count.ToString();
               }
             }