Question

我有一个页面，它会在Page_Load事件期间通过从SQL Server加载项目来填充两个下拉列表，因此，打开页面时可能需要一些时间来加载。目前，下拉列表将异步加载，但仍会降低页面加载速度。如何在页面完全加载后加载这些下拉列表？

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
   If Not IsPostBack Then
      LoadDDL()
   End If
End Sub

Public Sub LoadDDL()
    Try
        Dim cnnStr As String = DBMgr1.asyncADOCnnStr("SQLDS")


        '===== Load Scheme DDL =====
        Dim cnnScheme As SqlConnection = New SqlConnection(cnnStr)
        cnnScheme.Open()

        Dim SchemeStr As String = "SELECT " & _
                                    "CASE CODE " & _
                                        "WHEN 'P-PFC' THEN 'PFC' " & _
                                        "ELSE CODE " & _
                                    "END AS [SchemeCode], " & _
                                    "CASE DESCR " & _
                                        "WHEN 'P-PFC' THEN 'P-PFC/C-PFC' " & _
                                        "ELSE CODE " & _
                                    "END AS [SchemeName] " & _
                                "FROM i_Library WHERE MODULE = 'SYS' AND TYPE = 'Schemes' AND Stat1 = 'ACT' " & _
                                "AND Code <> 'C-PFC' " & _
                                "ORDER BY DESCR DESC"

        Dim cmdScheme As New SqlCommand(SchemeStr, cnnScheme)
        cmdScheme.CommandType = CommandType.Text
        Dim arScheme As IAsyncResult = cmdScheme.BeginExecuteReader()
        '===== Load Scheme DDL =====


        '===== Load Branch DDL =====
        Dim cnnBranch As SqlConnection = New SqlConnection(cnnStr)
        cnnBranch.Open()

        Dim BranchStr As String = "" & _
                                    "SELECT Distinct TeamCode " & _
                                    "FROM v_staff " & _
                                    "ORDER BY TeamCode " & _
                                    " "
        Dim cmdBranch As New SqlCommand(BranchStr, cnnBranch)
        cmdBranch.CommandType = CommandType.Text
        Dim arBranch As IAsyncResult = cmdBranch.BeginExecuteReader()
        '===== Load Branch DDL =====


        '===== Load Region Code DDL =====
        Dim cnnRegion As SqlConnection = New SqlConnection(cnnStr)
        cnnRegion.Open()

        Dim RegionStr As String = "" & _
                                    "SELECT Distinct RegionCode " & _
                                    "FROM v_staff " & _
                                    "WHERE RegionCode IS NOT NULL " & _
                                    "ORDER BY RegionCode " & _
                                    " "
        Dim cmdRegion As New SqlCommand(RegionStr, cnnRegion)
        cmdRegion.CommandType = CommandType.Text
        Dim arRegion As IAsyncResult = cmdRegion.BeginExecuteReader()
        '===== Load Region Code DDL =====


        'wait for the Scheme Query to return result
        arScheme.AsyncWaitHandle.WaitOne()
        Dim drScheme As SqlDataReader = cmdScheme.EndExecuteReader(arScheme)
        While drScheme.Read
            ddlScheme.DataSource = drScheme
            ddlScheme.DataTextField = "SchemeName"
            ddlScheme.DataValueField = "SchemeCode"
            ddlScheme.DataBind()

            ddlScheme.Items.Insert(0, "Select Scheme")
            ddlScheme.Items(0).Value = CMM.sExcVal1
        End While

        'wait for the Branch Query to return result
        arBranch.AsyncWaitHandle.WaitOne()
        Dim drBranch As SqlDataReader = cmdBranch.EndExecuteReader(arBranch)
        While drBranch.Read
            ddlBranch.DataSource = drBranch
            ddlBranch.DataTextField = "TeamCode"
            ddlBranch.DataValueField = "TeamCode"
            ddlBranch.DataBind()

            ddlBranch.Items.Insert(0, "Select Branch")
            ddlBranch.Items(0).Value = CMM.sExcVal1
        End While

        'wait for the Region Query to return result
        arRegion.AsyncWaitHandle.WaitOne()
        Dim drRegion As SqlDataReader = cmdRegion.EndExecuteReader(arRegion)
        While drRegion.Read
            ddlRegionCode.DataSource = drRegion
            ddlRegionCode.DataTextField = "RegionCode"
            ddlRegionCode.DataValueField = "RegionCode"
            ddlRegionCode.DataBind()

            ddlRegionCode.Items.Insert(0, "Select Region")
            ddlRegionCode.Items(0).Value = CMM.sExcVal1
        End While

        drScheme.Close()
        drBranch.Close()
        drRegion.Close()
        cnnScheme.Close()
        cnnBranch.Close()
        cnnRegion.Close()

    Catch ex As Exception
        MSGMgr.errHandlerSys(ex.Message, lblMsg)
    End Try
End Sub

Answer 1

或许使用ajax方法？

Answer 2

在你的页面中，编写这个js方法，它需要一个父项和一个子项下拉列表，它将根据父下拉列表的选定值异步填充子下拉列表：

  function LoadDataHandle(cmbParent,cmbChild,Type) {
            var cmb = document.getElementById(cmbParent);
            var mydate = new Date()
            mydate.setDate(mydate.getDate())

            $.get("GetItems.aspx?ID=" + cmb.value + "&Type=" + Type + "&x=" + mydate.getMilliseconds(), function(data) {
            LoadData(data, cmbChild);
        });

    }

function LoadData(strData, cmbChild) {
    var cmb = document.getElementById(cmbChild);
    cmb.options.length = 0;
    var choose = document.createElement('option');
    choose.text = "--- اختر ---";
    choose.value = -1;
    cmb.add(choose);
    if (strData.length > 0) {
        var data = strData.split('$');
        var i = 0;
        for (i = 0; i < data.length - 1; i++) {
            var data1 = data[i].split('#');
            var item = document.createElement('option');
            item.value = data1[0];
            item.text = data1[1];
            cmb.add(item);
        }
    }
}

请注意，使用jqyery的$ get方法传入查询字符串中包含parentid的aspx页面。

现在在包含下拉列表的aspx页面的page_load事件中

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    cmdParent.Attributes.Add("onchange", "LoadDataHandle('" & cmdParent.ClientID & "','" & cmdChild.ClientID & "');")
End Sub

我们差不多完成了，请注意，在GetItems.aspx时代，您需要将子项下拉项中应填写的项目写为单个长字符串，其中每个项目用“＃”分隔。这是一个这样做的样本：

 Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    Dim ID As Integer = Request.QueryString("ID")
Response.Write(GetDepartment(ID))
    End Sub

        Private Function GetDepartment(ByVal ID As String) As String
            Dim dt As DataTable = 'get from db
            If dt IsNot Nothing AndAlso dt.Rows.Count > 0 Then
                Dim sb As New StringBuilder(dt.Rows.Count * 20)
                For Each row As DataRow In dt.Rows
                    sb.AppendFormat("{0}#{1}$", row(0), row(1))
                Next
                Return sb.ToString
            End If
            Return ""
        End Function

Answer 3

我必须这样才能让它发挥作用。

首先，在.aspx文件中，我输入了一个隐藏的输入，该输入具有我想从javascript访问的元素的正确ID：

<input type='hidden' id='dropdownelem1ID' value='<%= DropdownElem1.ClientID %>' />

然后，正如MikeW指出的那样，只需要进行ajax调用，最好使用jQuery，然后填写结果。

为了得到正确的元素，我会使用这样的东西：

$('#' + $('#dropdownelem1ID').val())

Answer 4

所有用户的下拉内容是否相同，至少有一段时间？如果是这样，您可以将生成的HTML缓存在用户控件中。

否则，除了Ajax / jQuery之外，您还可以使用Silverlight发出WCF调用以检索下拉列表的内容并将其写入DOM。

异步填充下拉列表

4 个答案: