當ListItem不存在時DropDownList拋出錯誤

Question

我正在使用的應用程序是Service Desk應用程序。我有一個使用DropDownList的表單，其中包含來自Active Directory的員工姓名。任何員工都可以提出請求並保存。

當員工離開公司並因此將他的帳戶從Active Directory中刪除時出現問題。當其他員工搜索數據庫以查找可能使用的相關服務故障單時，當嘗試打開它時，會引發一個錯誤消息，指示名稱在DropDownList項中不存在。

我需要的是一個解決方案，以便功能保持不變（能夠刪除Active Directory條目），但不會引發錯誤。

我正在使用如標籤所示，ASP.NET與VB。使用C＃解決方案也是受歡迎的。

非常感謝您對我的問題提出的建議。

UPDATE：

我加入一些代碼，以便它可以更清楚。

ASPX：（這是巨大的，我只把DropDownList的問題）

<asp:FormView ID="FormView1" runat="server" DataSourceID="SqlDataSource1" 
     DataKeyNames="ITRequestId"> 
     <EditItemTemplate> 
      <br /> 
      <asp:LinkButton ID="LinkButton5" runat="server" CausesValidation="True" 
       CommandName="Update" Text="Update" CssClass="InsertLink" /> 
      &nbsp;&nbsp;&nbsp;<asp:LinkButton ID="LinkButton6" runat="server" 
       CausesValidation="False" CommandName="Cancel" Text="Cancel" CssClass="CancelLink" /> 

        ........  

        <div id="user" style="float: left;"> 
         <label>User:<asp:RequiredFieldValidator ID="RequiredFieldValidator9" runat="server" ErrorMessage="User" Display="Dynamic" ControlToValidate="DropDownList5" Text="*" ForeColor="#FF0000"></asp:RequiredFieldValidator></label><br /> 
         <asp:DropDownList ID="DropDownList5" runat="server" SelectedValue='<%# Bind("ITRequestUserName") %>'> 
          <asp:ListItem Value=""></asp:ListItem> 
          <asp:ListItem Value="All">All</asp:ListItem> 
          <asp:ListItem Value="NA">N/A</asp:ListItem> 
         </asp:DropDownList> 
        </div> 

        ......... 
     </EditItemTemplate> 

後面的代碼VB：（這是巨大的，但我把其中拋出錯誤的頁面加載事件）

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load 
    If (Not IsPostBack) Then 
     If Request.UrlReferrer IsNot Nothing Then 
      ViewState("RefUrl") = Request.UrlReferrer.ToString() 
     End If 
    End If 
    'Handles the mode of the FormView according to the request 
    If Request.QueryString.Get("ITRequestId") IsNot Nothing Then 
     FormView1.DefaultMode = FormViewMode.ReadOnly 
     Dim tName As String = DirectCast(FormView1.Row.FindControl("DropDownList5"), DropDownList).SelectedValue 
     Dim temptype As String = DirectCast(FormView1.Row.FindControl("DropDownList1"), DropDownList).SelectedItem.Text 
     Dim myAD As New tActiveDirectory(LDAPpath) 
     Dim lName As String = HttpContext.Current.User.Identity.Name.ToString() 
     Dim sDisplayName As String = myAD.GetUserInfo(lName, "displayName") 
     Dim cName As String = DirectCast(FormView1.Row.FindControl("Label5"), Label).Text 
     If Not (User.IsInRole("Developers") Or User.IsInRole("Administrators") Or tName = sDisplayName Or cName = sDisplayName) Then 
      If (temptype = "Access rights") Then 
       Response.Redirect("../IT/ITAccessDenied.aspx") 
      End If 
     End If 
     If Not (User.IsInRole("Developers") Or User.IsInRole("Administrators") Or cName = sDisplayName) Then 
      If (temptype = "Account") Then 
       Response.Redirect("../IT/ITAccessDenied.aspx") 
      End If 
     End If 
     If Not (User.IsInRole("LocalIT")) Then 
      If (temptype = "Internal IT Task") Then 
       Response.Redirect("../IT/ITAccessDenied.aspx") 
      End If 
     End If 
    Else 
     FormView1.DefaultMode = FormViewMode.Insert 
     Dim tempstatus As DropDownList = DirectCast(FormView1.Row.FindControl("DropDownList2"), DropDownList) 
     tempstatus.SelectedIndex = 3 
    End If 
End Sub 

聲明tName變量時，錯誤在代碼的第11行拋出。發生這種情況的原因是，數據庫中的用戶名以及將由DropDownList限制的UserName已從ActiveDirectory中刪除，因此它不存在於List的值中。

這裏是填充的DropDownList代碼：

Protected Sub FormView1_ItemCreated(ByVal sender As Object, ByVal e As System.EventArgs) Handles FormView1.ItemCreated 
    Dim d1 As DropDownList 
    Dim d2 As DropDownList 
    Dim myAD As New tActiveDirectory(LDAPpath) 
    Dim users As New ArrayList() 
    users = myAD.GetAllUsersInfo() 
    d1 = DirectCast(FormView1.Row.FindControl("DropDownList5"), DropDownList) 
    d2 = DirectCast(FormView1.Row.FindControl("DropDownList7"), DropDownList) 
    d1.DataSource = users 
    d2.DataSource = users 
End Sub 

Public Function GetAllUsersInfo() As ArrayList 
     Dim Users As New ArrayList() 
     Dim myDirectory As New DirectoryEntry(sPath) 
     Dim mySearcher As New DirectorySearcher(myDirectory) 
     Dim fullName As String 
     mySearcher.Filter = "(&(objectCategory=person)(objectClass=user))" 
     mySearcher.PropertiesToLoad.Add("sn") 
     mySearcher.PropertiesToLoad.Add("displayName") 
     mySearcher.Sort.PropertyName = "sn" 
     mySearcher.Sort.Direction = SortDirection.Ascending 
     Users.Add("") 
     Users.Add("N/A") 
     Users.Add("All") 
     For Each result As DirectoryServices.SearchResult In mySearcher.FindAll 
      fullName = result.Properties("displayName")(0).ToString 
      Users.Add(fullName) 
     Next 
     Return Users 
    End Function 

任何幫助，這將不勝感激。謝謝。

Answer 1

您的問題沒有太多關於代碼的細節。但它聽起來像你的應用程序試圖在DDL中選擇一個不存在的值（已經存在）。選擇這樣的前幾個檢查：

Dim ddl As DropDownList 
Dim item As ListItem = ddl.Items.FindByValue("Kostopoulos") 
If item IsNot Nothing Then 
    ddl.SelectedIndex = ddl.Items.IndexOf(item) 
Else 
    ddl.Items.Add(New ListItem("Not available")) 
    ddl.Enabled = False 
End If 

Answer 2

首先你應該從下拉列表找到的ListItem像

ListItem li=DropdownID.Items.FindByValue(""); 
    if (li != null) 
    DropdownID.SelectedValue = li.Value; 

詳情見msdn