ASP.NET and ADO.NET
Bind the DataReader to a DataGrid
Dim strConn As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source
= c:\sales2k.mdb"
Dim objConn As New OleDbConnection(strConn)
Dim strSQL As String = "select * from customer;"
Dim objComm As New OleDbCommand(strSQL, objConn)
Dim Results As String
objConn.Open()
Dim objDataReader As OleDbDataReader
objDataReader = objComm.ExecuteReader()
DataGrid1.DataSource = objDataReader
DataGrid1.DataBind()
Demo: VS to FrontPage – PageLoad
Page.IsPostback
Select Rating from a RadiobuttonList
Private Sub RadioButtonList1_SelectedIndexChanged(ByVal sender As System.Object,
ByVal e As System.EventArgs) Handles RadioButtonList1.SelectedIndexChanged
Dim strConn As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source =
c:\sales2k.mdb"
Dim objConn As New OleDbConnection(strConn)
Dim strSQL As String = "select * from customer where rating = '" &
RadioButtonList1.SelectedItem.Value & "'"
Dim objComm As New OleDbCommand(strSQL, objConn)
Dim Results As String
objConn.Open()
Dim objDataReader As OleDbDataReader
objDataReader = objComm.ExecuteReader()
DataGrid1.DataSource = objDataReader
DataGrid1.DataBind()
End Sub
ListControl Base Class
• DropDownList, ListBox, CheckBoxList,
RadioButtonList
• Properties:
– AutoPostBack
– DataSource
– DataTextField: The field in the datasource that provides
the text to be used for the list items.
– DataValueField
– SelectedItem, SelectedValue, SelectedIndex
• Note: Value of the selected item: SelectedItem.Value
• Event: OnSelectedIndexChanged
Some Possible Causes of Error
• The procedure in the Page_Load event is executed
everytime the web page is loaded.
– 1. The AutoPostBack property must set to True for the
OnSelectedIndexChanged event to work.
– 2. If the ListItems are created by the Items.Add method,
items may be added again.
– 3. The ADO.Net objects and binding do not need to be
recreated every time.
• If not page.isPostBack then …
• Demo: ASPNET/ListBoxPostback.aspx
Private Sub Page_Load(ByVal sender As System.Object, ByVal
e As System.EventArgs) Handles MyBase.Load
If Not Page.IsPostBack Then
ListBox1.Items.Add("Apple")
ListBox1.Items.Add("Orange")
ListBox1.Items.Add("Banana")
End If
End Sub
Binding a DataReader to a ListBox
• DataSource:
– ListBox1.DataSource =
objDataReader
• DataTextField:
– ListBox1.DataTextField = "CID"
• DataValueField:
– ListBox1.DataValueField = "CNAME"
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Private Sub Page_Load(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles MyBase.Load
If Not Page.IsPostBack Then
Dim strConn As String =
"Provider=Microsoft.Jet.OLEDB.4.0;Data Source = c:\sales2k.mdb"
Dim objConn As New OleDbConnection(strConn)
Dim strSQL As String = "select * from customer;"
Dim objComm As New OleDbCommand(strSQL, objConn)
objConn.Open()
Dim objDataReader As OleDbDataReader
objDataReader = objComm.ExecuteReader()
ListBox1.DataSource = objDataReader
ListBox1.DataTextField = "CID“
ListBox1.DataValueField = "CNAME"
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ListBox1.DataBind()
End If
End Sub
Private Sub ListBox1_SelectedIndexChanged(ByVal sender As System.Object,
ByVal e As System.EventArgs) Handles ListBox1.SelectedIndexChanged
Response.Write(ListBox1.SelectedItem)
Response.Write(ListBox1.SelectedValue)
End Sub
Display Selected Customer in dataGrid
Private Sub ListBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles ListBox1.SelectedIndexChanged
Dim strConn As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source =
c:\sales2k.mdb"
Dim objConn As New OleDbConnection(strConn)
Dim strSQL As String = "select * from customer where cid = '" &
ListBox1.SelectedItem.Value & "'"
Dim objComm As New OleDbCommand(strSQL, objConn)
objConn.Open()
Dim objDataReader As OleDbDataReader
objDataReader = objComm.ExecuteReader()
DataGrid1.DataSource = objDataReader
DataGrid1.DataBind()
End Sub
The Effects of PostBack on Bound Controls
• If the databinding is done in a PageLoad event
procedure without checking postback, the
databinding is repeated and the control is
initialized to its original state.
• For list controls, such as ListBox, CheckboxList,
and Radiobuttonlist, the selected item is no longer
selected.
• Note: Demo previous example without checking
postback.
Demo:ReaderUpdate.Aspx
• Use a DataReader to create a dropwdownList with
customer CIDs..
• Display selected customer data in textboxes.
• Update customer’s rating using Command object’s
ExecuteNonQuery method.
Private Sub Page_Load(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles MyBase.Load
If Not Page.IsPostBack Then
Dim strConn As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data
Source = c:\salesDB.mdb"
Dim objConn As New OledbConnection(strConn)
Dim strSQL As String = "select cid from customer;"
Dim objComm As New OledbCommand(strSQL, objConn)
objConn.open()
Dim objDataReader As oledbDataReader
objDataReader = objComm.executeReader()
ListBox1.DataSource = objDataReader
ListBox1.DataTextField = "CID"
ListBox1.DataBind()
objConn.close()
End If
End Sub
Private Sub ListBox1_SelectedIndexChanged(ByVal sender As
System.Object, ByVal e As System.EventArgs) Handles
ListBox1.SelectedIndexChanged
Dim strConn As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data
Source = c:\salesDB.mdb"
Dim objConn As New OleDbConnection(strConn)
Dim strSQL As String = "select * from customer where cid= '" &
ListBox1.SelectedItem.Text & "'"
Dim objComm As New OleDbCommand(strSQL, objConn)
objConn.Open()
Dim objDataReader As OleDbDataReader
objDataReader = objComm.ExecuteReader()
objDataReader.Read()
TextBox1.Text = objDataReader("cname")
TextBox2.Text = objDataReader("city")
TextBox3.Text = objDataReader("rating")
objDataReader.Close()
objConn.Close()
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles Button1.Click
Dim strConn As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data
Source = c:\salesDB.mdb"
Dim objConn As New OleDbConnection(strConn)
Dim strSQLUpd As String = "Update customer set rating = '" &
TextBox3.Text & "'"
strSQLUpd = strSQLUpd & " where cid='" &
ListBox1.SelectedItem.Text & "'"
Dim objCommUpd As New OleDbCommand(strSQLUpd, objConn)
objConn.Open()
objCommUpd.ExecuteNonQuery()
objConn.Close()
End Sub
DataSet Techniques Demos
• Dataform wizard
– Parent/child
• Adapter wizard
– DataBind
– Demo: Using view to display customers with
selected rating.
• Using code
Persistence of Data between Page Postback
• Each page is entirely new each time we submit
information to the same page. There is no
persistence of information between pages (other
than the ViewState which remembers the data
contained in controls). Variables and ADO objects
are lost.
• We can store variables and ADO objects in
Session or Application.
• Demo: StateTestCounter.ASPX, PersistDataSet.Aspx
Increase Counter by One. What is wrong?
<script runat="server">
dim counter as integer
sub Page_Load()
counter=0
end sub
sub IncreaseCounter(sender as object, e as
EventArgs)
counter=counter+1
response.write("The counter's value is:" +
cstr(counter))
end sub
Demo: StateTestCounter.ASPX
Save Counter in Session
Demo: StateTestCounter2.ASPX
<script runat="server">
dim counter as integer
sub Page_Load()
if not page.isPostBack then
counter=0
session("MyCounter")=counter
else
counter=session("MyCounter")
end if
end sub
sub IncreaseCounter(sender as object, e as EventArgs)
counter=counter+1
response.write("The counter's value is:" +
cstr(counter))
session("MyCounter")=counter
End sub
Save the Dataset in Session
Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles
MyBase.Load
If Not Page.IsPostBack Then
OleDbDataAdapter1.Fill(DataSet11)
OleDbDataAdapter2.Fill(DataSet11)
Session("myDataSet") = DataSet11
Else
DataSet11 = Session("MyDataset")
End If
End Sub
Private Sub RadioButtonList1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles RadioButtonList1.SelectedIndexChanged
Dim myView As DataView
Dim Rating As String
If RadioButtonList1.SelectedValue = "A" Then
Rating = "A"
ElseIf RadioButtonList1.SelectedValue = "B" Then
Rating = "B"
Else
Rating = "C"
End If
myView = DataSet11.Tables("customer").DefaultView
myView.RowFilter = "rating='" & Rating & "'"
DataGrid1.DataSource = myView
DataGrid1.DataBind()
End Sub
Demo: Binding to an ArrayList
Dim fruits As New ArrayList()
Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs)
Handles MyBase.Load
'If Not Page.IsPostBack Then
fruits.Add("apple")
fruits.Add("orange")
fruits.Add("banana")
CheckBoxList1.DataSource = fruits
CheckBoxList1.DataBind()
'End If
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)
Handles Button1.Click
Dim i As Integer
For i = 0 To CheckBoxList1.Items.Count - 1
If CheckBoxList1.Items(i).Selected Then
Response.Write("you check" & CheckBoxList1.Items(i).Text)
End If
Next
End Sub
Binding to an ArrayList (Collection) of Objects
Dim emps As New ArrayList()
Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles
MyBase.Load
If Not Page.IsPostBack Then
Dim myEMp1 As New Emp()
myEMp1.eid = "e1"
myEMp1.ename = "peter"
myEMp1.salary = 5000
Dim myEmp2 As New Emp()
myEmp2.eid = "e2"
myEmp2.ename = "paul"
myEmp2.salary = 6000
emps.Add(myEMp1)
emps.Add(myEmp2)
RadioButtonList1.DataSource = emps
RadioButtonList1.DataTextField = "eid"
RadioButtonList1.DataValueField = "salary"
RadioButtonList1.DataBind()
Session("MyEmps") = emps
End If
End Sub
Private Sub RadioButtonList1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles RadioButtonList1.SelectedIndexChanged
emps = Session("MyEmps")
Response.Write(emps.Item(RadioButtonList1.SelectedIndex).ename)
Response.Write(emps.Item(RadioButtonList1.SelectedIndex).salary.ToString)