Why does my counter variable not increment in this VB.NET code sample?

I have the following code

Protected Sub btnAdd_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnAdd.Click

    Dim counter As Integer = 0
    Dim t As DataTable = DirectCast(Session("MyDataTable"), DataTable)
    Dim row1 As DataRow = t.NewRow()



    If (isUnique(t) And counter < 30) Then
        row1("ID") = counter + 1
        row1("univirsityID") = ddlUnivs.SelectedValue
        row1("majorID") = ddlMajors.SelectedValue
        row1("UniName") = ddlUnivs.SelectedItem.Text
        row1("MajorName") = ddlMajors.SelectedItem.Tex开发者_如何转开发t
        t.Rows.Add(row1)
        Session("MyDataTable") = t
        GridView1.DataSource = t
        GridView1.DataBind()
        lblMsg.Text = "تم اضافة الرغبة"
        counter = counter + 1

    Else
        lblMsg.Text = "سبق لك ادخال الرغبة"
    End If

End Sub

The problem is the row1("ID") dose not change it keeps getting the value of 1 for all rows added to datatable any help is appreciated thanks in advance.

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Remove your current counter declaration (for the reasons everyone has been posting) and put this on top of your class:

Public Property Counter() As Integer
     Get
         Return IIf(ViewState("counter") Is Nothing, 0, CInt(ViewState("counter")))
     End Get
     Set(ByVal value As Integer)
         ViewState("counter") = value
    End Set
End Property

This way you are saving your counter variable in the statefull ViewState of your page, and it won't get lost after a page-cycle.

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With this line

Dim counter As Integer = 0

You are setting the counter every single time you click the button.

You need to store the counter in session or some other way.

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Counter will always be 0 as you reinitialise it on entry to the method.

Is there supposed to be a for loop in there somewhere?

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The problem is that you're initializing the counter variable to 0 every time that you click the button. You will need to move counter to the next higher level and save it somewhere between postbacks. I would suggest creating a session variable and saving it in there.

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I'd venture to guess you're actually looking for an identity column in the database. Otherwise your ID could be duplicated, which is no bueno.

Are you looking to do a loop in this code? There's no loop, so counter starts out at zero and gets 1 added. This could only insert one row.

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counter is a local variable, and it's going out of scope when the sub ends. That's why it is not incrementing.