' USED TO REFRESH THE PAGE WHIN IT IS POSTED BACK
If (IsPostBack = False) Then
' USED TO DISPLAY DEFAULT FIRST ITEM IN THE DROPDOWN
Dim Li1 As New ListItem()
Li1.Text = "ALL"
Li1.Value = ""
cboStudy.Items.Add(Li1)
' USED TO COUNT THE STUDIES IN THE DROPDOWN
If (objDS.Tables(0).Rows.Count <> 0) Then
' USED TO CIRCULATE LOOP UPTO THE RECORD COUNT
Dim i As Integer
For i = 0 To objDS.Tables(0).Rows.Count - 1
' USED TO CREATE NEW ITEM IN THE DROPDOWN
Dim Li As New ListItem
Li.Text = objDS.Tables(0).Rows(i)("Study_Desc").ToString()
Li.Value = objDS.Tables(0).Rows(i)("Study_ID").ToString()
'USED TO ADD ITEMS IN THE DROPDOWN
cboStudy.Items.Add(Li)
Next
End If
'USED TO SAVE THE CHANGES IN DATASET
objDS.AcceptChanges()
' USED TO CLOSE THE DATABASE CONNECTION
objDS.Dispose()
End If
End If
I have to read dataset in javascript. So that I have to bind Study_Desc in DropDownList.
How can I do that?
I believe you might find it useful to review how an ASP.NET page works and how it renders. In your particular case you are setting the contents of a dropdownlist to your dataset. This will then render a 'select' object to the user with the appropriate entries without the need for Javascript. This all occurs on the server-side, which is processed on the server before a HTML response to given back to the user.
With Javascript, this code runs on the client-side, i.e. the user's computer. Here it is possible to retreive your dataset (by this, the dataset will get serialised to be passed over the wire and read into a format that Javascript can read) and have it interact on the client-side. The question is, in your case, is why bother as you're rendering the dropdown on the server-side. If you are interested in pushing your dataset to Javascript, check out the links on this post for a selection of approaches you can take.
Minor notes:
In your code you're using the 'AcceptChanges' method when there is absolutely no reason to use this unless you're making a change(s) to the dataset which I'm guessing you're not in the PageLoad...
Related
I am relatively new to programming so please bare with me if I use improper terminology for the question I am about to ask.
Currently, I have a list(of String) that I am populating with 2 values that I am pulling from a database. Code Below.
objCn.Open()
sqlTermSelect.Connection = objCn
sqlTermSelect.CommandText = "Select PartsTerm, LaborTerm FROM SKU INNER JOIN Agreement On SKU.SKU = Agreement.SKU WHERE Agreement = #Agreement"
sqlTermSelect.Parameters.Add("#Agreement", SqlDbType.VarChar, 50).Value = txtAgreement.Text
Dim termDA As New SqlDataAdapter(sqlTermSelect)
Dim termDT As New DataTable()
termDA.Fill(termDT)
For i As Integer = 0 To termDT.Rows.Count - 1
listValues.Add(termDT.Rows(i)("PartsTerm").ToString())
listValues.Add(termDT.Rows(i)("LaborTerm").ToString())
Next
objCn.Close()
I am then storing the values of this list in two variables that I use as checks to see whether certain controls on my page should be enabled/visible or disabled/invisible.
The page that this is affecting operates(for lack of a better word) in two ways, the first is a brand new page with empty controls that the user fills out. The second way is if the user begins to fill out the page and leaves, the data they filled out is saved and they can return later to continue filling it out (I am not 100% certain but I believe when a user returns to an "in progress" page it is a post back, I could be wrong, I'm not terribly sure how this is handled).
The problem I am having comes to when this list is populated with the database values. When I go to a brand new page, the list is populated and the controls mentioned above are enabled/disabled appropriately with no issues, the issue arises when I go to an "in progress" page the list values don't populate and the controls that should be disabled are enabled. Essentially, I am looking for a way to populate this list every time a page is opened, "in progress" or brand new. The code above that populates the list is in the PageLoad() event and I have verified that it is not in a "If Not IsPostBack" statement.
Any and all help would be greatly appreciated, if there is anything I should add to this post code related I would be more than happy to supply it.
I have a usercontrol in an ASP NET web application on which I create dropdown lists based on some loaded data (from an XML file via a component in the BIN directory)
I found that I couldn't retrieve the values across postbacks, and I've been doing a fair bit of reading to figure out why. What I would like someone to explain is why the following condition exists:
Dim dd As New DropDownList
With dd
.Items.Add(New ListItem("First Item"))
.Items.Add(New ListItem("Second Item"))
.Items.Add(sts(0))
.Items.Add(sts(1))
.Items.Add(sts(2))
.Items.Add(New ListItem("Third Item"))
End With
AddHandler dd.SelectedIndexChanged, AddressOf changed
divControls.Controls.Add(dd)
In the code above the three items 'First Item', 'Second Item' and 'Third Item' all behave correctly, as you can see they are added directly to the dropdown box in code. The items sts(0), sts(1) and sts(2) are all loaded from an XML file into either an array or list of string
Interestingly, sts(0) always posts back correctly, but any subsequent items which are added from the dynamic source don't. I've tried a bunch of ways of getting my list of strings into the dropdown so that they are still there upon postback but I'm not having much luck, would be most grateful if anyone could shed some understanding on this
I figured it out - I need to give each ListItem a value, I had lazily coded just the text portion since I wasn't using ordinals in the list, but ASP NET needed the ordinal value, or the list item value, to register the item for event validation, I expect ASP NET was only able to give subsequent items in the array or list of string the same ordinal or listitem value as all the other members of the collection, since they are from the same object. Works now!
Not done any programming for about 5 years so im a little rusty on this one.
I am building an Asset management system to make my job easier but am struggling on a few things.
What i have so far is the DB setup and populated with a small amount of data, The main site itself is built and the basic select statements to a gridview of any data currently in the system for that particular page/search and i also have an insert statement that is populating the relevant tables based on data filed in on a form on that page. All these functions are working seamlessly.
The problem i have is that one field that needs to be populated for the insert statement needs to populate based upon the selection that is being made from a drop down box in the same form.
i.e.
An Asset that is being registered into the system has an Asset Type (the type details are contained within a parent table Asset_Type) the form has 3 fields for display purposes (one of these fields will need to return an entry to the Asset table in the database from the form, this is working) that are taken from the Asset_Type table, the other fields only relate to the Asset table itself.
What i am trying to achieve is that a user goes to the page and sees a list of Assets registered (this is working) they then need to add a new asset by filling in a form lower down on the page (for is there and writes to DB) on this form is a drop down menu that queries the Asset_Type table and allows the user to select the Type by name (this works)
What i now need to get working is for the 2 other fields to populate based on what Asset type is selected.
These fields are currently textboxes in the form but can be changed if required.
The code i have behind the page is below:
Protected Sub Name_Model_SelectedIndexChanged(sender As Object, e As EventArgs) Handles Name_Model.SelectedIndexChanged
Using conn As New SqlConnection(ConfigurationManager.ConnectionStrings("AssetManagementConnectionString").ToString())
Dim cmd As New SqlCommand()
cmd.Connection = conn
cmd.CommandText = "SELECT [ID], [Name_Model], [Description_Spec] FROM [Asset_Type] WHERE ([ID] = #ID)"
cmd.CommandType = CommandType.Text
conn.Open()
Dim reader As SqlDataReader = cmd.ExecuteReader()
If reader.HasRows Then
While (reader.Read())
{
Type_ID.text = (reader["ID"].tostring())
Name_Model.text = (reader["Name_Model"].tostring())
Description_Spec.text = reader["Description_Spec"].tostring
}
End While
End If
End Using
End Sub
So I'm not sure about Steve's comment, but I know he is a lot more familiar with VB based on questions of my own he has answered. However I am going to suggest something.
So "Drop downs" typically have 2 pieces of data associated with them.
A DisplayMember and a ValueMember (also a SelectedValue if it's a ComboBoxColumn)
You can reference either, I believe.
Then, you can do what you please with that value using an If Then or however you plan on using it.
assetValue = YourComboBox.DisplayMember.ToString
YourTextBox.Text = assetValue
or
If ComboBox.ValueMember = YourIndex Then
assetValue = Whatever
ElseIf
....
End If
Give that a try and let me know what you get. I am just throwing ideas out there.
I'm having a hard time with this scenario and hoping someone can help me clarify where I'm missing a step/logic. I tried searching online but I couldn't find an example that addressed this issue.
We are setting up a search page that when first loads shows a bunch of options (e.g., textboxes, checkboxes, etc). The user will fill out the form and submit the form back to itself. Once posted back, the page will build and run a SQL query (e.g., SELECT ID FROM Customers WHERE Company = 'Acme' AND AmtDue = 3) against the database with the user's options and then the results will show up. This part works ok.
The part that breaks down is when I am trying to add pagination. The result set is a DataTable bound to a Repeater. I am using a PagedDataSource to add pagination. Pagination works great for the first page but for subsequent pages, it does not work. Basically, instead of returning the next page of the result requested (e.g., SELECT ID FROM Customers WHERE Company = 'Acme' AND AmtDue = 3), the results returned is the SQL query before appending the user's search options (e.g., SELECT ID FROM Customers).
I think my basic problem is that I'm not sure how to distinguish a normal Page.IsPostBack and paginating through results. The reason why this is causing problems is because I don't want to be regathering form data, rebuilding query, and requerying the DB.
The examples that I found online involved pagination of a DataTable that is rebuilt every time the page loads (e.g., Not Page.IsPostBack).
Here is a rough outline of our code:
Public dtCustomers As DataTable = New DataTable()
Sub Page_Load(ByVal Sender As Object, ByVal E As EventArgs) Handles Me.Load
' When the page first loads, show the search form with search options.
If Not Page.IsPostBack Then
ShowSearchForm()
' Once the form is submitted, show the search results.
Else
' ----------------------------------------
' This is the part that I'm having trouble with. How do I skip the following two steps (GatherFormData() and BuildDT()) when the user requests a subsequent page?
GatherFormData()
dtCustomers = BuildDT()
' ----------------------------------------
BindData()
End If
End Sub
Sub BindData()
Dim objPDS As PagedDataSource = New PagedDataSource()
objPDS.DataSource = dtCustomers.DefaultView
objPDS.AllowPaging = True
objPDS.PageSize = intNumPerPage
objPDS.CurrentPageIndex = Me.ViewState("_CurrentPage")
rptSearchResults.DataSource = objPDS
End Sub
' Subroutine called when the previous page button is pressed.
Sub GoToPrevPage()
' Set viewstate variable to the previous page.
Me.ViewState("_CurrentPage") -= 1
BindData()
End Sub
' Subroutine called when the next page button is pressed.
Sub GoToNextPage()
' Set viewstate variable to the next page.
Me.ViewState("_CurrentPage") += 1
BindData()
End Sub
Note: I understand that the DataTable will have to be put into cache or a session variable, but haven't decided the best method.
Please excuse the code outline but the actual code is massive so the simplification is to make it easier to get to the heart of the issue.
Let me know if any of that was unclear. Thanks in advance!
I am assuming that you are going to store your data in session/cache (I would prefer the later but there can be use case for storing it in session) - you can store the key in the view-state and presence of key could be use to determine if post-back is for pagination or not. For example,
if (ViewState["dataKey"] == null)
{
// first form submittal, do the search
GatherFormData();
dtCustomers = BuildDT();
// store it in cache
ViewState["dataKey"] = Guid.NewGuid().ToString(); // create a key
Cache.[ViewState["dataKey"].ToString()] = dtCustomers; // TODO use Add method to control expiration etc
}
Its important that you clear the view-state when the search is reset (or similar condition)
Lastly, it is also possible to do the paging from database/data-store (for example, using ranking functions in SQL Server) so that you need not have to store the search results into the session/cache but rather do a database trip at each post-back. Such approach is useful when the complete result set size can be huge.
I am trying to use datasource and bind in my application to set a dropdown list to the results of a query. The dropdownlist populates correctly (shows each different type_name in the set) but later when I use ddltype.selectedvalue - I am always getting the value from the first item in the dataset. Here is the code.
if ds.hasRows = true
ddlType.DataValueField = "type_id"
ddlType.DataTextField = "type_name"
ddlType.DataSource = ds
ddlType.DataBind()
end if
Then later on I use the following code to try to get teh selected value
Dim typeID = ddlType.SelectedValue
I have ran the query to get the dataset on my SQL server and get the below results - but every time I use the above dim statement, the value is set to 812 even when type 2 is selected. Below is the results from the query that fills the sqldatareader named ds.
type_id : type_name
___________________
812 : type one
813 : type two
Thanks in advance.
Based on the information in your question, I don't see anything wrong.
But based on common mistakes people make with this pattern, I am guessing you are probably running ddlType.DataBind() on every postback. So the user clicks a button or something similar to fire the postback, and the DDL is re-bound before your click handler checks the value. Re-binding sets the selectedvalue back to default.
Edit: Your databinding code in Page_Load should only run once. One way to do this is to wrap the databinding code...
If Not IsPostBack Then
If ds.hasRows = True Then
ddlType.DataValueField = "type_id"
ddlType.DataTextField = "type_name"
ddlType.DataSource = ds
ddlType.DataBind()
End If
End If
This will cause the databinding to occur only the first time the page is requested, but not after a button click or other postback action.