我想在回发时保留一个数组

Question

I have a page where someone is going to input a string. There will be a button to submit, but also we want this page to work with a scanner so it posts back when it scans. That part I will worry about later.

What I want right now is to be able to enter a string in the textbox, hit submit, and it save that string to an array. Then the textbox is cleared and they can enter another string. It will save this string to the array and repeat. After the user has all the strings in they want, there will be another button to do something else (not important). So it will grab all the strings in the array and execute some code.

Right now I cannot seem to get the array to keep the information. I'm trying to use ViewState for the first time in my life, and I see the string when I come back in from postback, but I can't save that string to the array.

I hope this makes sense

Protected jobs() As String
Protected i As Integer = 0

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

If Not ViewState("jobs") Is Nothing Then
    jobs(i) = ViewState("jobs").ToString
    i += 1
End If

Protected Sub btnAddToBatch_Click(sender As Object, e As EventArgs) Handles btnAddToBatch.Click
    If txtJob.Text <> "" Then
        ViewState("jobs") = txtJob.Text
    End If
End Sub

Answer 1

I have figured it out incase anyone is interested.

Protected jobs(0) As String
Protected i As Integer = 0 

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

If Not ViewState("jobs") Is Nothing Then
    jobs = ViewState("jobs")
    i = ViewState("i")
End If

End Sub

Protected Sub btnAddToBatch_Click(sender As Object, e As EventArgs) Handles btnAddToBatch.Click

If txtJob.Text <> "" Then
    If i = 0 Then
        ReDim jobs(0)
    Else
        ReDim Preserve jobs(jobs.Length)
    End If
    jobs(i) = txtJob.Text
    i = i + 1
    ViewState("i") = i
    ViewState("jobs") = jobs
End If

End Sub

Answer 2

I would set the list up like this:

Public MyList As New List(Of String)

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

    If IsPostBack = False Then
       ' first time page load - put MyList into session()
        Session("Mylist") = MyList
    Else
        ' page post back - pull list from session
        MyList = Session("MyList")
    End If

End Sub

Protected Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click

    ' add a value to a text box on say simple button click

    Debug.Print(TextBox1.Text)

    MyList.Add(TextBox1.Text)


End Sub

Protected Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click

    Debug.Print("number in list = " & MyList.Count)

    Debug.Print("First value in list = " & MyList.Item(0))

    ' display all items in list

    For Each s As String In MyList
        Debug.Print(s)
    Next

End Sub

Note how we don't even have to shove back the MyList into session(). It like any object is a pointer to the Mylist in session. The above will also work equal well with viewstate.

As you can see, by using a list in place of a array, we don't have to re-dim, we don't have to have a extra "i" value, and the list can expand as we place. Also, the list has other cool features like

    MyList.Contains        - search  the list for a match
    MyList.Sort()          - sort the list

So, not only is the list dynamic, does not require re-dim, but you can also search and search the list without having to write looping code. Even in VBA, I tend now days to use a collection or list - they are just oh so much less code, easier to work with, and as noted you get extra features like searching with "contains", and even sorting abilities. And even with all these features you wind up writing less code, and in FEW cases have to deal with a loop based on a integer value to get values out of the array.

Array's quite much go back to the old days of say FORTRAN or the older PC "basic" languages, and now with lists or collections, we have not only better choices, but those choices are less code, less effort and more flexbile.

And this is not really a huge deal - but as you can see, by using the on-load event of the given web page, we ONLY one spot and ONLY in one location have to set up the value - since it is a object, then further code can simply add/change or do whatever to the MyList, and we are NOT required to shove the MyList back into session - since the on-load event takes care of this process. Setting MyList from session() means the MyList is "pointing" to the object in session - and this is why I don't even have to save the list back to session, but ONLY set it up one time on page load. Any and all other events such as button code etc. is now free to add to that list or do whatever - and NO need to send/save the MyList back to session is required with the above setup.