listbox selects wrong item - asp.net

Update I have solved the issue, however will finish posting this (solved prior to posting) in hopes it might help someone else out.
Issue: Referencing and manipulating listitems from a listbox requires the listbox's listitems to all have unique listbox.value. In my case, I was assigning the tablename as the listbox value and the columname as the listbox.text(I was giving the user a list of fields from a sql table to choose from). So a listbox containing the following:
Index 0: Text:street Value:"dbo.incident"
Index 1: Text:city Value:"dbo.incident"
Index 2: Text:state Value:"dbo.incident" Selected
And you then reference textbox1.selected item via code, it's handling is unexpected.
It starts off knowing the selected item, but at some point in it's handling of the referenced listitem, it starts referencing it via value, at which point the return text or index would be 'street' or '0'. I understand once you start pulling items from a listbox, it pulls its first match.
begin original post
Okay project is a vb .net web forms project
I have 2 listboxes that I want to populate and move entries back and forth, up and down.
I understand how to do this, however i cannot seem to overcome this bizzare errant behavior that is happening.
If I add items manually like this it works fine, the listitems transfer between the listboxes and I can change the indexes as expected.
(for this post, I will refer to entries created this was as static)
ListBox1.Items.Add(New ListItem("1", "1"))
...through...
ListBox1.Items.Add(New ListItem("10", "10"))
However if I add them programaticly from a linq statement, manual selection in the web page holds no bearing on selected item, it is always 0, clicking any button on the page, postback returns the listbox to index 0.
(for this discussion, I will refer to entries created this way as dynamic)
Dim db As New MSCRMDataContext
Dim datamodel = db.Mapping
For Each r In datamodel.GetTables
If r.TableName = "dbo.IncidentFull" Then
For Each r1 In r.RowType.DataMembers
ListBox1.Items.Add(New ListItem(r1.MappedName, r.TableName))
Next
End If
Next
I have an aspx button:
<asp:Button ID="Button1" runat="server" Text="Button" />
That has the following click event:
Protected Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
mlbs_transferitem(ListBox1, ListBox2, ListBox1.SelectedItem)
End Sub
I have the sub that transfers the listitem in a separate .vb file
Public Class multilistboxselector
Shared Sub mlbs_transferitem(srclb As ListBox, dstlb As ListBox, lbitem As ListItem, Optional sort As Boolean = False)
'checks if srclb had a selected listitem
If IsNothing(lbitem) Then
Exit Sub
End If
'check for dupes
For Each li As ListItem In dstlb.Items
If li.Text = lbitem.Text Then
If li.Value = lbitem.Value Then
Exit Sub
End If
End If
Next
'add lbitem to dst
dstlb.SelectedIndex = -1
dstlb.Items.Add(lbitem)
'remove lbitem from src
srclb.Items.Remove(lbitem)
'sort dst
If sort = True Then
End If
End Sub
Just to be clear, the code works flawlessly with the static entries. I have created a new page and recreated everything there and the I have the same experience as my source page.
Edit
Trimming out my troubleshooting steps as they prove irrelevant to the issue and were quite lengthy.

Related

Get child page data from master page selectedItems

I have location DropdownList in my master page. I have set control in my child page which takes properties from master page. Now I am running a query
SELECT * FROM table where city like '"+city.text+"'
here city.text gets value from master page selected cities. But my problem is it's not actually showing records as per city.text has values in it. It shows any random records.
My Code
Master Page
<asp:DropDownList ID="locationSelector" runat="server" AutoPostBack="true">
<asp:ListItem Selected>Pune</asp:ListItem>
<asp:ListItem>Delhi</asp:ListItem>
<asp:ListItem>Chennai</asp:ListItem>
<asp:ListItem>Bangalore</asp:ListItem>
<asp:ListItem>Mumbai</asp:ListItem>
</asp:DropDownList>
Child page VB Code
Dim location As DropDownList = Page.Master.FindControl("locationSelector")
city.Text = location.SelectedItem.ToString
If Not IsPostBack Then
Try
query = "SELECT * FROM hospitals where city like '" + city.Text + "'"
Dim cmd As New MySqlCommand(query, con)
cmd.CommandTimeout = 120
Dim da As New MySqlDataAdapter(cmd)
Dim table As New DataTable
da.Fill(table)
ViewState("Data") = table
hospitals.DataSource = table
hospitals.DataBind()
Catch ex As Exception
Response.Write(ex)
End Try
End If
UPDATE
Protected Sub hospitals_PreRender(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.PreRender
Dim location As DropDownList = Page.Master.FindControl("locationSelector")
city.Text = location.SelectedItem.ToString
End Sub
Sometimes it also throws TimeOut error. But most of the time It gets results but not as per selected items. What will be any other solution for this?
A couple of tips:
1) Timeout errors can happen for a number of reasons, including lots of other traffic to the site, connection pools all used up etc. I would, for a small list of cities, maybe keep that in a cache after the first call, so that you do not need to load the city list from database every time. Depending on your country, if you only have a few thousand cities, then just put it in an in-memory list.
2) You are using a "SELECT *" which is usually not really cool to other developers, nor to your code if the table contains more than just a city name. IF you write Select CityName from Table, then you will effectively have reduced the amount of data going from your database to your program, and it is clear to the other developers exactly what you're pulling from that table.
3) If you have an ID for the city, it will likely perform even better as string matcing is REALLY slow compared to matching a couple of ID's. I've seen 20% speed improvements by replacing strings with constants, you wouldn't believe how slow strings are in code these days.
4) Last, and I think you may already have done this, make sure that you INDEX every field that you do a WHERE filter on. If you search for Hospitals, then make sure that the Hospitals.City field is indexed to avoid row lookups.
I hope (any) of this helps you :)
As per my understanding you need to change below
to fetch the selected TEXT value use location.SelectedItem.Text instead of location.SelectedItem.ToString()
city.Text = location.SelectedItem.Text // change here
before binding the dropdown control check the no. of rows
if(table.Rows.Count>0)
{
hospitals.DataSource = table;
hospitals.DataBind();
}
I would suggest to use prerender event within page. In prerender event try to access your master page control and get value.

value of variables not changing in asp.net

currently I am working on a project named online exam.
All the controls are dynamically created.
I have a webpage where I want to display the student details.
I displayed those details correctly in a table.
Now here comes the time to edit those details.
To edit a record I use the linked button named edit.
When a user clicks on that Linked button the data in that row is replaced with new textboxes.
Upto here I am OK.
Now when I click on the save changes button after making changes to the textboxes.
The old values are not replaced by the new values and the old values remains.
The code for creating textboxes in the table is as follows :
Public Sub Edit_Click(ByVal sender As Object, ByVal e As System.EventArgs)
For x As Integer = 0 To EditList.Count - 1
If sender.id.substring(4) = EditList(x).ID.Substring(4) Then
Session("PreviousRollNo") = RollNoList(x).Text
Dim txtName As New TextBox
txtName.Text = NameList(x).Text
NameList(x).Text = ""
NameList(x).Parent.Controls.Add(txtName)
txtList.Add(txtName)
Dim txtCourse As New TextBox
txtCourse.Text = CourseList(x).Text
CourseList(x).Text = ""
CourseList(x).Parent.Controls.Add(txtCourse)
txtList.Add(txtCourse)
Dim txtAdmissionDate As New TextBox
txtAdmissionDate.Text = AdmissionList(x).Text
AdmissionList(x).Text = ""
AdmissionList(x).Parent.Controls.Add(txtAdmissionDate)
txtList.Add(txtAdmissionDate)
Dim btnSaveChanges As New Button
btnSaveChanges.Text = "Save Changes"
EditList(x).Text = ""
EditList(x).Parent.Controls.Add(btnSaveChanges)
AddHandler btnSaveChanges.Click, AddressOf btnSaveChanges_Click
Session("EditButtonClicked") = True
Dim btnCancel As New Button
btnCancel.Text = "Cancel"
DeleteList(x).Text = ""
DeleteList(x).Parent.Controls.Add(btnCancel)
AddHandler btnCancel.Click, AddressOf btnCancel_Click
Session("CancelButtonClicked") = True
txtName.Focus()
Exit For
End If
Next
End Sub
The code for Save Changes button is as follows :
Public Sub btnSaveChanges_Click(ByVal sender As Object, ByVal e As System.EventArgs)
If txtList(0).Text = "" Then
Dim trError As TableRow = New TableRow
Dim tdError As TableCell = New TableCell
tdError.ColumnSpan = 7
Dim lblError As New Label
lblError.Text = "Please enter name of the student."
lblError.ForeColor = Drawing.Color.Red
tdError.Controls.Add(lblError)
trError.Controls.Add(tdError)
tbl.Controls.Add(trError)
ElseIf txtList(1).Text = "" Then
Dim trError As TableRow = New TableRow
Dim tdError As TableCell = New TableCell
tdError.ColumnSpan = 7
Dim lblError As New Label
lblError.Text = "Please enter the course."
lblError.ForeColor = Drawing.Color.Red
tdError.Controls.Add(lblError)
trError.Controls.Add(tdError)
tbl.Controls.Add(trError)
ElseIf txtList(2).Text = "" Then
Dim trError As TableRow = New TableRow
Dim tdError As TableCell = New TableCell
tdError.ColumnSpan = 7
Dim lblError As New Label
lblError.Text = "Please enter the Admission Date"
lblError.ForeColor = Drawing.Color.Red
tdError.Controls.Add(lblError)
trError.Controls.Add(tdError)
tbl.Controls.Add(trError)
Else
Dim cb As New OleDbCommandBuilder(da)
Dim editRow() As DataRow
editRow = ds.Tables("Student_Detail").Select("Roll_No = '" & Session("PreviousRollNo") & "'")
editRow(0)("Name") = txtList(0).Text
editRow(0)("Course") = txtList(1).Text
editRow(0)("Admission_Date") = txtList(2).Text
da.Update(ds, "Student_Detail")
Page.Response.Redirect("ChangeUserDetails.aspx")
End If
End Sub
I get the error sying that array is out of the bounds. on the first line of the btnSaveChanges_Click.
It means txtlist is always cleared when I click on Save Changes Button.
So I stored txtList in a Session like Session("txtList") = txtList.
and retrieved the data from that. But now I get the old values of the textbox instead of the newer ones.
Here txtList is a list (of Textbox)
Firstly, welcome to the ASP.NET WebForms Page Life Cycle. Remember its pattern with the simple mnemonic: SILVER = Start, Init, Load, Validate, Events, Render.
Secondly, HTTP is stateless. WebForms does an amazing job of hiding this fact from you using ViewState until you do something a little out of the ordinary (as you're now attempting), and it all appears to fall apart. What's really happening is that you're starting to see side-effects of how WebForms is managed, and how it's not as much like WinForms (or another stateful system) as you might think.
When you're responding to an event server-side in WebForms, it's easy to get the impression that nothing has changed. That the entire page is as you left it "last time". All the controls are there, the values you may have set programatically are still set. Magic. Not magic. What's actually happened is the entire page has been re-constructed to respond to that event. How was it re-constructed? By a combination of your page definition (markup), actions taken in control event handlers, and the form data posted back by the client.
Confusing? OK, let's consider an example. Say you've got a page with two controls on it. A textbox named txtInput and a button named btnSubmit with event handler btnSubmit_Click. When the user first requests the page, the HTML for these controls is derived from your markup (aspx page) and returned to the client. Next, the user sets a value in txtInput and clicks the submit button. The server then re-creates the page from scratch based on your markup. At this early stage of the life-cycle, the controls still have their default values. We then hit the Load stage of the life-cycle, and "if the current request is a postback, control properties are loaded with information recovered from view state and control state." In other words, by the time the life-cycle gets to Init, the control has been created from markup, but still has its default value. The Load stage then sets the value according to Postback data.
Left wondering how this applies to your scenario? You're adding your dynamic controls in response to a control event. There's two things wrong with that:
It's too late in the page life-cycle for Init to set the values based on data posted back from the client (recall SILVER, Event is after Init).
Your button click event handler is only run once, in response to the postback where the user clicked the button. But remember on each postback the page is entirely re-created. So the dynamic controls no longer exist as far as the server is concerned! You'll notice that not only are the controls not present server side when responding to the submit event, but after the page has handled it, they're no longer present client-side either.
So what's the answer? Well the "Life-Cycle Events" section of the page I linked offers a clue. It states that the PreInit event be used to (among other things) "Create or re-create dynamic controls". Why would we do it in PreInit? So it's early enough in the page life-cycle for the later events to properly handle it (like setting the values posted back from the client).
Now, I know, you want to add the controls based on the user clicking on the button. How does that fit? The trick is that you've got to manage the "state" yourself. Huh? the state? By this I mean MyDynamicControlsShouldBeShown = true / false. When the button is clicked, creating the controls in response to the button-click event handler is the right action (there's not really any choice there). But you need to store that state somehow so you know on subsequent requests to the page, whether those controls should be re-created in PreInit. One neat option would be to check for the ID of your dynamic control in Request.Form.Keys. If the control ID is present in the Keys collection, then the user is posting back a value for the control, so you should re-create it.
A side-note on the use of Session
Hopefully based on the above you've realised why putting the controls into Session didn't work. But to be clear, the controls you put into the Session object were no longer part of a page that existed (remember, the page gets completely re-created for each request. Those controls were no longer hooked up to the Page events, so didn't get their values populated between Page Init and Load. If somehow it did work, it still wouldn't be a particularly good idea, as Session is not per-request. So what would happen if a user had the same page open in multiple tabs? Strange things, that's what.

Add New Item to Already Bound ListView in ASP Net (Unable to set DataKeys/FieldName)

My overall goal is to add fake/unbound items to a listview control (for final HTML Table output reasons). This is a code behind solution. Users will not be adding items as it will be outputted in a rigid table.
I have looked at several examples and while this is easy for a dropdown it is not for listview.
The code below works without error, but my item is not shown on runtime. I think the class is not setting the item fieldname correctly, but I can't figure out the right syntax to fix it.
ColumnNameAList.DataSource = PeriodDataView
ColumnNameAList.DataBind()
Dim test As New Example1("ColumnNameA")
Dim newItem As New ListViewDataItem(ColumnNameAList.Items.Count, ColumnNameAList.Items.Count)
newItem.DataItem = test
ColumnNameAList.Items.Insert(ColumnNameAList.Items.Count, newItem)
ColumnNameAList.Items.Add(newItem)
Here is the Example1 class that is supposed to set the DataValueField:
Public Class Example1
Public Sub New(ColumnNameA__1 As String)
ColumnNameA = ColumnNameA__1
End Sub
Private m_ColumnNameA As String
Public Property ColumnNameA() As String
Get
Return m_ColumnNameA
End Get
Set(value As String)
m_ColumnNameA = value
End Set
End Property
End Class
This outputs my original datasource list, but not the added item.
<ItemTemplate>
<td>
<%# Eval("ColumnNameA")%>
</td>
</ItemTemplate>
In the end I could only reliably solve this with a codebehind solution.
I made a copy of the original datasource, modified my copy and then databound to it.
Dim MyOriginalTableSource As Data.DataView = DataManager.example()
Dim ModifiedTable As DataTable = MyOriginalTableSource.ToTable
'do stuff here
Mylistbox.DataSource = ModifiedTable
Mylistbox.DataBind()
Won't work for everyone, but in this case it works fine for me.
There could be a couple of issues with the way you are approaching this, including that the ListView is already databound and that you are both adding and inserting the newItem.
When we have a scenario like this, we take one of two approaches:
1) Add the new item to the data source before the source is data bound.
2) Remove databinding and manually create each of the list view items, then add your new item at the beginning or end of the loop.
Another way to do it would be to inject it into the sql.
select col1, col2, col3 from table1 union select '1','2','3'
this would ensure that the item is always added, and asp.net doesn't need to know or care.
You can add this into the sql query or add it from the behind code before binding query. if you are not binding with sql, you can also do this to any list item with LINQ

ASP.NET Dynamic User Controls

I'm sure this question has been asked a million times, however I haven't been able to find an answer that solves my problem.
I am programmatically adding some custom user controls to a PlaceHolder which I have on a simple aspx page. All of the user controls Postback's work correctly except for one which has a Gridview on it.
For some reason any postback that gets fired from within this control, does not call the specified event on the first click, however all future clicks it will work fine. I have no idea why this is the case, but many solutions I have found, suggest adding an ID to the ascx User Control, however this doesn't work in my case.
I've taken a look at the source file for the page that gets generated before and after the first click, javascript used for calling the postback changes, i.e
Before first click: onclick="javascript:__doPostBack('tmpControlID$sgvPrimaryEmploymentHistory','Select$0')"
After first click: onclick="javascript:__doPostBack('OFFHome1$tmpControlID$sgvPrimaryEmploymentHistory','Select$0')"
OFFHome1 is the parent user control which exists on the aspx page. All other controls are added to a placeholder in this control, i.e.
<%# Control Language="vb" AutoEventWireup="false" CodeBehind="OFFHome.ascx.vb" Inherits="UmbracoUserControls.OFFHome" %>
<asp:PlaceHolder ID="phOFFSection" runat="server"></asp:PlaceHolder>
Nothing to complicated. Then in the code behind the controls are loaded into the placeholder using the following:
Private Sub LoadNextOFFStep()
Dim ControlName As String = "TestControl.ascx"
phOFFSection.Controls.Clear()
If ControlName IsNot Nothing AndAlso ControlName <> String.Empty Then
Dim NewControl As Object = LoadControl(ControlName)
With NewControl
.ID = USERCONTROLNAME
Dim StepCompleted As Boolean = .FillControl()
If StepCompleted Then
Exit Sub
End If
Dim AllowSkip As Boolean = .AllowSkip()
btnSkip.Visible = AllowSkip
End With
phOFFSection.Controls.Add(NewControl)
End If
End Sub
Again, nothing overly complicated. The USERCONTROLNAME is just a const with the value "tmpControlID" in it.
The control that is giving me trouble is a little complicated, I was originally using a custom GridView control that we have created, but have removed it and replaced it with the standard asp one to see if the problem still occurs, and it does.
Any button, on control which fires off a postback will fail the first time, and all future click will work correctly. On the first click the Page_Load event will get called, but that is it.
What am I doing wrong??
After far too much time spent on this, I have finally worked it out.
It was to do with the order of events, however just not where I had thought. The FillControl function was getting called before User Control had been added to the PlaceHolder. I changed this so that it gets called after the User Control was added to the PlaceHolder and now it works first time.
Basically the code looks like this now:
Private Sub LoadNextOFFStep()
Dim ControlName As String = "TestControl.ascx"
phOFFSection.Controls.Clear()
If ControlName IsNot Nothing AndAlso ControlName <> String.Empty Then
Dim NewControl As Object = LoadControl(ControlName)
With NewControl
.ID = USERCONTROLNAME
Dim AllowSkip As Boolean = .AllowSkip()
btnSkip.Visible = AllowSkip
End With
phOFFSection.Controls.Add(NewControl)
Dim StepCompleted As Boolean = CType(phOFFSection.Controls(0), Object).FillControl()
If StepCompleted Then
LoadNextOFFStep()
Exit Sub
End If
End If
End Sub
Thanks for everyone's help.
Well... the answer to the first question is simple: It fails the first time because the ID of the control (or rather, in the postback script) is different on subsequent page loads. It works on subsequent clicks because the control ID stays the same.
Now as to WHY that is... much tougher! But probably something to do with the order of operations here.
Try explicitly setting the NamingContainer value for NewControl:
With NewControl
.NamingContainer = OffHomeOne; // whatever
.ID = USERCONTROLNAME

DropDownList SelectedIndex value not updating on AutoPostback

It looks like this question was addressed here, but his solution did not work for me. I am creating a dynamic dropdown menu system that populates a secondary dropdownlist with the results of a query based on the selected item in the first dropdown.
First dropdown getting populated:
Dim db As New linqclassesDataContext
Dim categories = (From c In db.faq_cats)
NewFaqDropDownCategory.DataSource = categories
NewFaqDropDownCategory.DataTextField = "category"
NewFaqDropDownCategory.DataValueField = "category_id"
NewFaqDropDownCategory.DataBind()
Unset(categories)
Unset(db)
Second dropdown getting populated:
Protected Sub NewFaqDropDownCategory_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs)
Dim temp As Integer = CInt(Val(NewFaqDropDownCategory.SelectedIndex))
MsgBox(theDrop.SelectedValue)
Return
'Dim db As New linqclassesDataContext
'Dim faqs = (From f In db.faqs Where f.category = NewFaqDropDownCategory.SelectedValue)
'NewFaqDropDownList.DataSource = faqs
'NewFaqDropDownList.DataTextField = "question"
'NewFaqDropDownList.DataValueField = "id"
'NewFaqDropDownList.DataBind()
'NewFaqLabel.Visible = True
'NewFaqDropDownList.Visible = True
'Unset(faqs)
'Unset(db)
End Sub
The markup for the first dropdown...
<asp:DropDownList ID="NewFaqDropDownCategory" AutoPostBack="true" runat="server" OnSelectedIndexChanged="NewFaqDropDownCategory_SelectedIndexChanged">
</asp:DropDownList>
And the second...
<asp:DropDownList ID="NewFaqDropDownList" runat="server" Visible="false">
</asp:DropDownList>
No matter what I have tried, I always get "1" (the value of the first item in the second dropdown). The post I referenced earlier said this had to do with AutoPostBack and the server not knowing the list was updated yet.
Can anyone clarify this for me a little more?
Set a break point on the line that reads: NewFaqDropDownCategory.DataBind() and one in your event handler (NewFaqDropDownCategory_SelectedIndexChanged).
I suspect the databind is being called right before your NewFaqDropDownCategory_SelectedIndexChanged event fires causing your selected value to change.
If so, you need either to make sure you only databind if you aren't in the middle of your autopostback or instead of using NewFaqDropDownCategory.SelectedIndex on the first line of your event handler you can cast the sender parameter to a DropDownList and use its selected value.
I had the same problem. Found I forgot to look if I was posting back to the page or not and I was binding my DropDownList control in the Page_Load event of the page.
I had forgot to use:
if (!IsPostBack)
{
.... do databind ....
}
I think there is a bug in your LINQ query for the second drop down box
Dim faqs = (From f In db.faqs Where f.category = NewFaqDropDownCategory.SelectedValue)
Here you are comparing SelectedValue to category. Yet in the first combobox you said that the DataValueField should be category_id. Try changing f.category to f.category_id

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