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In ASP with VB codebehind how do I present the user a yes/no dialog from VB

I have the following case where a user has selected a product, the product record has been retrieved and the backorder flag is set. I want to ask the user if the want to include it in the order anyway. I can't seem to find an exaample anywhere that demonstrates it in an IF statement.
My VB Code Snippet:
Dim backorder = myDataTable.Rows(0)("backorder").ToString()
If backorder = "True" And <somehow ask user it they want to order anyway> Then
'do something
End If
My Javascript in aspx file:
<script type = "text/javascript">
function Confirm() {
var confirm_value = document.createElement("INPUT");
confirm_value.type = "hidden";
confirm_value.name = "confirm_value";
if (confirm("Selected item is on temporary back order. Do yuou want to include it on this order?")) {
confirm_value.value = "Yes";
} else {
confirm_value.value = "No";
}
document.forms[0].appendChild(confirm_value);
}
</script>
I can read the variable being added, by javascript, to the page from VB, but can't figure how to call the javascript in order to prompt the user.
For some reason I can't get my head around this. Please advise with example.

Use the RegisterStartupScript method:
Sub ProcessOrder()
'Your code to process the selected products here...
Dim orderAnyway As string = hdnConfirmResponse.Value.Trim()
If selectedItem.BackOrdered Then
If orderAnyway = "" Then
Dim cs As ClientScriptManager = Page.ClientScript
' Define the name and type of the client scripts on the page.
Dim csname1 As String = "ConfirmScript"
Dim cstype As Type = Me.GetType()
' Check to see if the startup script is already registered.
If (Not cs.IsStartupScriptRegistered(cstype, csname1)) Then
Dim cstext1 As String = "Confirm();"
cs.RegisterStartupScript(cstype, csname1, cstext1, True)
End If
Else
If orderAnyway = "yes" Then
'ADD THE BACKORDERED ITEM SINCE THEY CONFIRMED
End If
End If
End If
End Sub

I hate answering my own question but this what finally worked. Mixture of mjw's answer and more research on my javasvript attempt. Rather than have JS create the hidden field, I added it to the HTML
<asp:HiddenField runat="server" id ="confirm_value"/>
New VB:
If myDataTableFrame.Rows.Count > 0 Then
Dim backorder = myDataTableFrame.Rows(0)("backorder").ToString()
If backorder = "True" And confirm_value.Value <> "Yes" Then
Dim cs As ClientScriptManager = Page.ClientScript
' Check to see if the startup script is already registered.
If (Not cs.IsStartupScriptRegistered(Me.GetType(), "ConfirmScript")) Then
Dim cstext1 As String = "Confirm();"
cs.RegisterStartupScript(Me.GetType(), "ConfirmScript", "Confirm();", True)
End If
Return
Else
confirm_value.Value = "No"
...
New Javascript:
See ASP.NET set hiddenfield a value in Javascript Also added a reclick of the button if they answered "OK"
<script type = "text/javascript">
function Confirm() {
if (confirm("Selected item is on temporary back order. If you want to include it on this order click OK, then resubmit it?")) {
//had to resort to this to find hidden field rather than document.getElementById('confirm_value')
var x = document.getElementById('<%= confirm_value.ClientID%>');
x.value = 'Yes';
//re-click the button
document.getElementById('<%=bttnadd.ClientID%>').click();
} else {
var x = document.getElementById('<%= confirm_value.ClientID%>');
x.value = 'No';
}
}
</script>

Enable button on ASP.NET after HttpResponse

I have button on my ASP.NET page which calls gets disabled on click(to prevent double click) and call this function:
Private Sub ExportToExcel(ByVal nameReport As String, ByVal wControl As GridView, ByVal sTitle As String)
Dim responsePage As HttpResponse = Response
Dim sw As New StringWriter()
Dim htw As New HtmlTextWriter(sw)
Dim pageToRender As New Page()
Dim form As New HtmlForm()
wControl.AllowPaging = False
wControl.EnableViewState = False
wControl.DataSource = GetDataSource(False)
wControl.DataBind()
wControl.Caption = "<strong>" + sTitle + "</strong>"
form.Controls.Add(wControl)
pageToRender.Controls.Add(form)
responsePage.Clear()
responsePage.Buffer = True
responsePage.ContentType = "application/vnd.ms-excel"
responsePage.AddHeader("Content-Disposition", "attachment;filename=" & nameReport)
responsePage.Charset = "UTF-8"
responsePage.ContentEncoding = Encoding.Default
pageToRender.RenderControl(htw)
responsePage.Write(sw.ToString())
responsePage.End()
End Sub
Which I use to export some data to Excel. Now I need to re-enable the button on client side when the HttpResponse is finished. How can I do that?

The Response.End() aborts the thread and sends the execution to Application_EndRequest. There is not much to do after that.
Please check this post. It presents a solution using iframes.

textbox value from client side in code behind?

I'm writing a website that is fully dynamic . means all controls are made by Response.write , no I have a problem , that after page load I want to get value of text boxs which made dynamically in code behind , but its not received by Request.Form , here is my code :
Private Function userconf() As string
Dim script As String
Dim conString As String = ConfigurationManager.ConnectionStrings("sqlexpress").ConnectionString
Using con As New System.Data.SqlClient.SqlConnection(conString)
Dim com As New SqlCommand("SELECT * FROM clientamount WHERE Mode <> 1 ", con)
con.Open()
Dim resultid As String
Dim reader As SqlDataReader = com.ExecuteReader()
Try
While reader.Read()
RenderBuyForm = RenderBuyForm + "<div><input id='tx" & reader("ID") & "' type='text' />" & reader("avrageamountunit") & "<input id='txd" & reader("ID") & "' type='text'/>"
End While
Finally
reader.Close()
End Try
End Using
Return RenderBuyForm
End Function
and this function loads in page_preload event :
Protected Sub Page_PreLoad(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.PreLoad
userconf()
End If
End Sub
and also in html page I have
<form id="form1" runat="server">
<%=RenderBuyForm%>
<asp:Button ID="Button1" runat="server" Text="Button" />
<asp:Label ID="Label1" runat="server" Text="Label"></asp:Label>
</form>
at least I try to read textboxes value are in html page now in Button1_Click event:
Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
For Each row As DataRow In tabel1.Rows
Dim a As String = Request.Form("tx" & tabel1.Rows(0)("ID") & "")
label1.text = a
Next
End Sub
but a is returning Nothing . can I ask you help me in this issue ? how can I read these textboxes value from client side in code behind ?

You will also need to add to
RenderBuyForm = RenderBuyForm + "<div><input id='tx" ....
RenderBuyForm = RenderBuyForm + "<div><input name='tx' & reader("ID") ..
in the userconf().

Getting asp:TextBox text property in codebehind from a web user control after a javascript update

Here is the scenario.
I have a simple page containing an asp:PlaceHolder.
<%# Page Title="" Language="VB" MasterPageFile="~/MasterPage.master" AutoEventWireup="false" CodeFile="TrainingPlan.aspx.vb" Inherits="TrainingPlan" %>
<%# Reference Control="ctlTask.ascx" %>
<%# Reference Control="ctlTaskheader.ascx" %>
<asp:Content ID="Content1" ContentPlaceHolderID="MainContent" Runat="Server">
<div class="centered">
<h2><asp:Label ID="lblPlanTitle" runat="server" Text="Plan Title"></asp:Label></h2>
<hr />
<br />
<asp:ImageButton ID="imgbtnSave" runat="server" ImageUrl="~/Images/save.ico" />
<br />
<asp:PlaceHolder ID="PlanPlaceHolder" runat="server"></asp:PlaceHolder>
</div>
</asp:Content>
The placeholder on this page is populated with several rows of the same web user control. This web user control contains several textboxes. For each textbox in this web user control I have public properties to set and get the text value. In the page load event of the web user control I am adding onClick attributes to some of those textboxes like so.
Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
txtTrainingStart.Attributes.Add("onClick", "txtTrainingStart_Click(" & txtTrainingStart.ClientID & ", " & txtTask.ClientID & ");")
txtTraineeBadgeNum.Attributes.Add("onClick", "txtTraineeBadgeNum_Click(" & txtTraineeBadgeNum.ClientID & ", " & txtTask.ClientID & ", " & txtTrainingStart.ClientID & ");")
txtTrainerBadgeNum.Attributes.Add("onClick", "txtTrainerBadgeNum_Click(" & txtTrainerBadgeNum.ClientID & ", " & txtTrainingComplete.ClientID & ", " & txtTask.ClientID & ", " & txtTraineeBadgeNum.ClientID & ", " & Session.Item("isTrainer").ToString.ToLower & ");")
txtDecertifyingOfficial.Attributes.Add("onClick", "txtDecertifyingOfficial_Click(" & txtDecertifyingOfficial.ClientID & ", " & txtTrainerBadgeNum.ClientID & ", " & txtTask.ClientID & ", " & Session.Item("isDecertifyingOfficial").ToString.ToLower & ");")
End Sub
For each of those onClick events I have corresponding javascript functions.
<script type="text/javascript">
function txtTrainingStart_Click(txtTrainingStart, txtTask) {
//processing and updates to textboxes here
}
</script>
Here is the problem.
On the main page containing the placeholder I have a save button. In the click event of the save button I am looping through each of the web user controls contained in the placeholder to process and save the data.
Protected Sub imgbtnSave_Click(sender As Object, e As ImageClickEventArgs) Handles imgbtnSave.Click
For Each item As Control In PlanPlaceHolder.Controls
Dim task As ctlTask = TryCast(item, ctlTask)
If Not IsNothing(task) Then
'need updated textbox values here.
'The following line gets the original textbox value, not the updated value that I need
Dim test As String = task.trainingStart
End If
Next
End Sub
Everything I have tried I can only get the original value that was in the textbox when the page loaded. I would think that this should be simple and I am just missing something basic. I've searched google high and low for the solution but I have yet to find one. This was the closest thing I found -> Set Text property of asp:label in Javascript PROPER way.
Although that post deals with a label rather than a textbox and isn't using a placeholder containing several web user controls. From what I understand I need to POST the updates back to the server from the client but I don't know how to do this. I've tried using the Request.Form property but I couldn't seem to make that work. What am I missing?
Thank you for any help,
Rylan
EDIT
Here is the code that populates the placeholder with the web user controls as requested
Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
Dim DBConn As MySqlConnection
Dim cmd As New MySqlCommand
DBConn = New MySqlConnection(Globals.mysqlConStr)
Try
lblPlanTitle.Text = Request.QueryString("plan_name") & " Training Plan"
If Session.Item("empID") = -1 Then
empID = clsUser.getID
Else
empID = Session.Item("empID")
End If
Dim strSQL As String = "SELECT * FROM task_revs tr WHERE tr.change != 'Deleted' and tr.id_plan = " & Request.QueryString("id_plan") & " ORDER BY task_num, rev_date desc"
Dim da As New MySqlDataAdapter(strSQL, DBConn)
Dim dtAllRevs As New DataTable
da.Fill(dtAllRevs)
Dim dtCurrentRev As New DataTable
Dim lastTaskNum As String = ""
dtCurrentRev = dtAllRevs.Clone
For Each row As DataRow In dtAllRevs.Rows
If lastTaskNum <> row("task_num") Then
dtCurrentRev.ImportRow(row)
lastTaskNum = row("task_num")
End If
Next
strSQL = "SELECT * FROM checkoffs WHERE emp_id = " & empID
da = New MySqlDataAdapter(strSQL, DBConn)
Dim dtCheckoffs As New DataTable
da.Fill(dtCheckoffs)
Dim addColor As Boolean = True
Dim tabWidth As Integer
Dim Header As ctlTaskHeader = LoadControl("ctlTaskHeader.ascx")
PlanPlaceHolder.Controls.Add(Header)
For Each row As DataRow In dtCurrentRev.Rows
Dim newRow As ctlTask = LoadControl("ctlTask.ascx")
tabWidth = 0
newRow.id_Task = row("id_Task")
newRow.taskNum = row("task_num")
newRow.task = row("task")
If row("is_header") = True Then
If row("task_num").ToString.EndsWith(".0") And row("task_num").ToString.Split(".").Count = 2 Then
newRow.taskBold = True
newRow.taskItalic = True
Else
newRow.taskForeColor = Drawing.Color.Blue
newRow.taskItalic = True
tabWidth += 10
End If
Else
tabWidth += 10
End If
For i As Integer = 0 To row("task_num").ToString.Split(".").Count - 3
tabWidth += 10
Next
newRow.TabSize = tabWidth
If Not IsDBNull(row("task_level")) Then
For i As Integer = 0 To row("task_level") - 1
newRow.taskLevel = newRow.taskLevel & "*"
Next
End If
If addColor = True Then
newRow.taskNumBackColor = Drawing.Color.LightGray
newRow.taskLevelBackColor = Drawing.Color.LightGray
newRow.taskBackColor = Drawing.Color.LightGray
newRow.trainingStartBackColor = Drawing.Color.LightGray
newRow.trainingCompleteBackColor = Drawing.Color.LightGray
newRow.traineeBadgeNumBackColor = Drawing.Color.LightGray
newRow.trainerBadgeNumBackColor = Drawing.Color.LightGray
newRow.decertifyingOfficialBackColor = Drawing.Color.LightGray
End If
addColor = Not addColor
For Each checkoff As DataRow In dtCheckoffs.Rows
If checkoff("id_task") = row("id_task") Then
If Not IsDBNull(checkoff("training_start")) Then
newRow.trainingStart = checkoff("training_start")
End If
If Not IsDBNull(checkoff("training_complete")) Then
newRow.trainingComplete = checkoff("training_complete")
End If
If Not IsDBNull(checkoff("trainee_badge")) Then
newRow.traineeBadgeNum = checkoff("trainee_badge")
End If
If Not IsDBNull(checkoff("trainer_badge")) Then
newRow.trainerBadgeNum = checkoff("trainer_badge")
End If
If Not IsDBNull(checkoff("decertifying_official")) Then
newRow.decertifyingOfficial = checkoff("decertifying_official")
newRow.taskNumBackColor = Drawing.Color.LightSalmon
newRow.taskLevelBackColor = Drawing.Color.LightSalmon
newRow.taskBackColor = Drawing.Color.LightSalmon
newRow.trainingStartBackColor = Drawing.Color.LightSalmon
newRow.trainingCompleteBackColor = Drawing.Color.LightSalmon
newRow.traineeBadgeNumBackColor = Drawing.Color.LightSalmon
newRow.trainerBadgeNumBackColor = Drawing.Color.LightSalmon
newRow.decertifyingOfficialBackColor = Drawing.Color.LightSalmon
End If
End If
Next
If row("is_header") = True And PlanPlaceHolder.Controls.Count > 1 Then
Dim newLine As LiteralControl = New LiteralControl("<br/>")
PlanPlaceHolder.Controls.Add(newLine)
End If
PlanPlaceHolder.Controls.Add(newRow)
Next
Catch ex As Exception
clsLog.logError(ex)
Finally
DBConn.Close()
End Try
EDIT 2
I thought it might also be important to show how I am making updates to the textboxes in my javascript functions
function txtTrainingStart_Click(txtTrainingStart, txtTask) {
var currentdate = new Date();
var datetime = (currentdate.getMonth() + 1) + "/" + currentdate.getDate() + "/" + currentdate.getFullYear() + " " + getTimeAMPM();
txtTrainingStart.value = datetime;
txtTrainingStart.style.backgroundColor = "yellow";
}

Edit 3:
The below code will work for static controls, but dynamically-created controls will not be preserved on postback. You will need to store the updated values so they can be retrieved on postback somehow (e.g. a Session variable or HiddenField). If possible, I would create the controls statically and populate them in page_load, hiding controls with no data - this would allow you to get the values on postback as below.
Hmm...I set up a super simplified version of your code and ran it pretty much as is (without the database function), and it seems to be working fine.
Here is the simplified version I used:
<asp:Content id="Content1" ContentPlaceHolderID="MainContent" runat="server">
<asp:ImageButton ID="imgbtnSave" runat="server"></asp:ImageButton>
<asp:PlaceHolder ID="PlanPlaceHolder" runat="server">
<asp:TextBox runat="server" ID="txtTrainingStart" value="before" ></asp:TextBox>
</asp:PlaceHolder>
</asp:Content>
Javascript:
function txtTrainingStart_Click(txtTrainingStart, txtTask) {
var currentdate = new Date();
var test = "after";
txtTrainingStart.value = test;
txtTrainingStart.style.backgroundColor = "yellow";
}
VB:
Protected Sub imgbtnSave_Click(ByVal sender As Object, ByVal e As ImageClickEventArgs Handles imgbtnSave.Click
For Each item As TextBox In PlanPlaceHolder.Controls
'need updated textbox values here.'
Debug.WriteLine(item.ID)
Debug.WriteLine(item.Text)
Next
End Sub
I'm getting the updated value of the textbox, so you should be able to pass that value to a function and do whatever operations you need.
Let me know if I'm missing something.
Edit 2: I just had a thought--can you check if page_load is being called after you click the save button? I wonder if it is overwriting your updated values with the original values again.
If it is, I would wrap the database functionality in page_load with a postback check:
If Not IsPostBack
' connect to database'
' populate placeholder'
End If

I have figured it out. I was on the right track using Request.Form I just didn't fully understand how to use it yet.
New code for my save button
Protected Sub imgbtnSave_Click(sender As Object, e As ImageClickEventArgs) Handles imgbtnSave.Click
Dim coll As NameValueCollection
coll = Request.Form
For x = 0 To coll.Count - 1
Response.Write("Key = " & coll.GetKey(x) & " Value = " & coll(x) & "<br />")
Next
End Sub
The loop outputs all the control keys and updated values from the postback like so.
Key = ctl00$MainContent$ctl01$txtTrainingStart Value = 8/1/13
Key = ctl00$MainContent$ctl01$txtTrainingComplete Value = 8/2/13
Key = ctl00$MainContent$ctl02$txtTrainingStart Value = 8/3/13
Key = ctl00$MainContent$ctl02$txtTrainingComplete Value = 8/4/13
I use a hidden field to store a database row id with each dynamically created web user control. From that point it's easy to insert the updated values into my database.

Passing Variable from JS to VB.net

I have a variable that gets a value in a js function. I need to get its value as a double into a vb.net variable.
I have tried putting the variable into a label then grabbing it from the label in vb.net as shown in the code below:
Js part.
document.getElementById("Label1").innerText = nwLat;
then in the vb part
Dim nwLat As Double
nwLat = Label1.Text
MsgBox(nwLat)
it does not work for me any ideas? the error that comes up is
Input string was not in a correct format.
Cheers!

Easiest way without any type of ajax would be to use a hidden field.
Markup:
<asp:HiddenField ID="nwLatHidden" runat="server" Value="" />
JS:
document.getElementById('nwLatHidden').value = '6.00'; // or of course the value from your function.
.NET during your postback routine:
Dim nwLat As Double
nwLat = nwLatHidden.Value

In JavaScript:
__doPostBack(
'edit',
JSON.stringify({ ID: id, Code: code, AcctNo: acctNo })
);
In VB.NET:
Protected Sub Page_Load(s As Object, e As EventArgs) Handles Me.Load
If Not Page.IsPostBack Then
'...
Else
Dim eventTarget As String = Request.Form!__EVENTTARGET
Dim eventArgument As String = Request.Form!__EVENTARGUMENT
If Not eventArgument Is Nothing AndAlso Not eventTarget Is Nothing AndAlso eventTarget = "edit" Then
Dim jss As New JavaScriptSerializer()
Dim ac As AccountCode = jss.Deserialize(Of AccountCode)(eventArgument)
End If
End If
End Sub

You need to use the ClientID or the UniqueID:
document.getElementById("<%=Label1.UniqueID%>").innerText = "Hi";