.<1> - }
Supporting Classes
DropDownService Class
VB.NET
Imports Microsoft.VisualBasic
Imports System.Data
Public Class DropDownService
Inherits System.Web.UI.Page
Protected _selectedValue As String
Protected _fcn As String
'----------------------------------------------------------------------------------------------
Public Overridable Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
_fcn = Request.QueryString("fcn")
_selectedValue = Request("sv")
If _selectedValue Is Nothing OrElse _selectedValue.Length = 0 Then
_selectedValue = "0"
End If
End Sub
'----------------------------------------------------------------------------------------------
Protected Function DropDownHtml(ByVal sourceTable As DataTable, ByVal textField As _
String, ByVal valueField As String) As String
Dim result As String = ""
result &= DropDownItemHtml("--Select One--", "", _selectedValue)
For Each row As DataRow In sourceTable.Rows
result &= DropDownItemHtml(row.Item(textField).ToString(), _
row.Item(valueField).ToString(), _
_selectedValue)
Next
Return result
End Function
'----------------------------------------------------------------------------------------------
Private Function DropDownItemHtml(ByVal text As String, ByVal value As String, ByVal _
selectedValue As String) As String
Dim result As String = ""
result &= "<option value='"
result &= value
result &= "' "
If value = selectedValue Then
result &= "selected='true' "
End If
result &= ">"
result &= text
result &= "</option>"
result &= vbCrLf
Return result
End Function
End Class
C#
TODO
ASPX Host Page
HTML Markup
Within the <%@ Page %> directive...
<%@ Page ... EnableEventValidation="false" ... %>
Within the <head> section...
<script type="text/javascript" src="Scripts/jquery.js"></script>
<script type="text/javascript" src="Scripts/MyPage.js"></script>
Within the <body> section...
<span id="ChannelDropDown">
<asp:DropDownList ID="uxChannelDropDown" runat="server" />
<br />
<asp:HiddenField Value="0" ID="uxChannelField" runat="server" />
</span>
<span id="ReasonDropDown">
<asp:DropDownList runat="server" ID="uxReasonDropDown" />
<br />
<asp:HiddenField Value="0" ID="uxReasonField" runat="server" />
</span>
ASPX Code-Behind
Note
Despite online postings to the contrary, the following code does NOT eliminate the Invalid postback or callback argument error. Instead, you must alter the <%@ Page %> directive as indicated above. Although this is a security risk, it is the only way I've found that resolves this issue.
VB.NET
Protected Overrides Sub Render(ByVal writer As System.Web.UI.HtmlTextWriter)
ClientScript.RegisterForEventValidation(uxChannelDropDown.UniqueID.ToString())
ClientScript.RegisterForEventValidation(uxReasonDropDown.UniqueID.ToString())
MyBase.Render(writer)
End Sub
C#
TODO
JavaScript Code
This code is in a separate javascript file that is loaded via a <script> tag.
//- Document Ready Function -----------------------------------------------------------------------
var uxDropDown1;
var uxDropDown2;
uxDropDown1 = "span#ChannelDropDown>select";
uxField1 = "span#ChannelDropDown>input";
uxDropDown2 = "span#ReasonDropDown>select";
uxField2 = "span#ReasonDropDown>input";
$(document).ready(function()
{
LoadPrimaryDropDown();
$(uxDropDown1).click(uxDropDown1_Change);
$(uxDropDown2).click(uxDropDown2_Change);
});
//- Load Categories Drop Down List ----------------------------------------------------------------
function LoadPrimaryDropDown()
{
$.get("ServiceWrapper.aspx",
{ fcn: "GetChannelsHtml"
,sv: $(uxField1).val()
},
function(data)
{
$(uxDropDown1).html(data);
uxDropDown1_Change();
});
}
//- Channel Drop Down Change Event Handler --------------------------------------------------------
function uxDropDown1_Change()
{
// retain new value for when we refresh after a postback
$(uxField1).val($(uxDropDown1).val());
// cascade: the selected category filters the available topics
$.get("ServiceWrapper.aspx",
{ fcn: "GetReasonsHtml"
,sv: $(uxField2).val()
,cid: $(uxDropDown1).val()
},
function(data)
{
$(uxDropDown2).html(data);
uxDropDown2_Change();
});
}
//- Reason Drop-Down Change Event Handler ---------------------------------------------------------
function uxDropDown2_Change()
{
$(uxField2).val($(uxDropDown2).val());
}
Service Code
This is the ASPX markup and code-behind file for the ServiceWrapper.ASPX page, which is called asynchronously by the JavaScript code above to populate the drop-downs. Note that this is NOT a web service page, but an ASPX page!
ASPX Markup
<%@ Page Language="VB" AutoEventWireup="false" CodeFile="ServiceWrapper.aspx.vb" Inherits="ServiceWrapper" %>
Code-Behind
VB.NET
Imports System.Collections.Generic
Imports System.Data
Partial Class ServiceWrapper
Inherits DropDownService
Private _channelId As String
'----------------------------------------------------------------------------------------------
Public Overrides Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
MyBase.Page_Load(sender, e)
If Not Integer.TryParse(Request("cid"), _channelId) Then
_channelId = 0
End If
Select Case _fcn
Case "GetChannelsHtml"
Response.Write(GetChannelsHtml())
Case "GetReasonsHtml"
Response.Write(GetReasonsHtml())
End Select
Response.End()
End Sub
'----------------------------------------------------------------------------------------------
Private Function GetChannelsHtml() As String
Dim nvc As NameValueCollection = New NameValueCollection()
nvc.Add("ReqType", "IPR")
Dim formVerId As Integer = Databases.OnlineForms.GetFormVersionId(nvc)
Dim t As DataTable = Databases.OnlineForms.GetFormSelectionOption(formVerId, "Channel")
Return MyBase.DropDownHtml(t, "AttributeText", "AttributeID")
End Function
'----------------------------------------------------------------------------------------------
Private Function GetReasonsHtml() As String
Dim nvc As NameValueCollection = New NameValueCollection()
nvc.Add("ReqType", "IPR")
Dim formVerId As Integer = Databases.OnlineForms.GetFormVersionId(nvc)
Dim t As DataTable = Databases.OnlineForms.GetFormSelectionOptionByParent( _
formVerId, "Reason", _channelId)
Return MyBase.DropDownHtml(t, "AttributeText", "AttributeID")
End Function
End Class
C#
TODO