爲什麼這個下拉不填充？

Question

我有三個下拉菜單;第二個（會員）根據第一個（單元）中的內容填充，第三個（客戶）應該基於第二個內容填充;但事實並非如此。

下面是在LINQPad工作查詢（返回公司名稱的列表）：

select distinct companyname from customers C left join members M on M.MemberNo = C.MemberNo where M.MemberNo = '052' order by companyname 

...但在下面的代碼不起作用：

'Populate the Members dropdown 
Dim selectedUnit As String = DropDownListUnits.Text 
Dim membersDT As DataTable 
sql = "select distinct shortname, M.memberno from members M left join memberunitproducts mup on M.MemberNo = mup.MemberNo where unit = '" + selectedUnit + "' order by shortname" 
retDS = sqlDAL.runSQLDataSet(sql) 
membersDT = retDS.Tables(0) 
DropDownListMembers.DataSource = membersDT 
DropDownListMembers.DataTextField = "shortname" 
DropDownListMembers.DataValueField = "memberno" 
DropDownListMembers.DataBind() 

'Populate the Customers dropdown 
Dim selectedMember As String = DropDownListMembers.DataValueField 
Dim customersDT As DataTable 
sql = "select distinct companyname from customers C left join members M on M.MemberNo = C.MemberNo where M.MemberNo = '" + selectedMember + "' order by companyname" 
retDS = sqlDAL.runSQLDataSet(sql) 
customersDT = retDS.Tables(0) 
DropDownListCustomers.DataSource = customersDT 
DropDownListCustomers.DataTextField = "companyname" 
DropDownListCustomers.DataValueField = "companyname" 
DropDownListCustomers.DataBind() 

第三（客戶）當這個運行時，下拉菜單仍然沒有填充 - 爲什麼？

它可能不是必要的，但在這裏是第一個（「單位」）下拉代碼：

'Populate the Units dropdown 
Dim unitsDT As DataTable 
sql = "Select distinct unit from masterunits where abs(active) = 1" 
retDS = sqlDAL.runSQLDataSet(sql) 
unitsDT = retDS.Tables(0) 
DropDownListUnits.DataSource = unitsDT 
DropDownListUnits.DataTextField = "unit" 
DropDownListUnits.DataValueField = "unit" 
DropDownListUnits.DataBind() 

我缺少什麼或者做錯了嗎？

Answer 1

我不得不改變這一點：

Dim selectedMember As String = DropDownListMembers.DataValueField 

...這樣的：

Dim selectedMember As String = DropDownListMembers.SelectedItem.Value