Problem with ArrayList

[nadaNuaim]

I have an arraylist and i define it as public variable

Public StockArray As New ArrayList

inside button1_click body
i append new elements in that Stockarray
by
dim stockobj as new stock // stock is a class

StockArray.Add( stockobj)

when i print any element of Stockarray within button1 body it works fine

but when i call the stockArray in a another button body the StockArray is empty !


any ideas will be Extremly helpful

[SammyB]

I have an arraylist and i define it as public variable

Public StockArray As New ArrayList

inside button1_click body
i append new elements in that Stockarray
by
dim stockobj as new stock // stock is a class

StockArray.Add( stockobj)

when i print any element of Stockarray within button1 body it works fine

but when i call the stockArray in a another button body the StockArray is empty !


any ideas will be Extremly helpful

Are you sure you placed StockArray in the correct place? Works for me:

Public Class Form1
	Public StockArray As New ArrayList
	Public iCounter As Integer = 0
	Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
		iCounter = iCounter + 1
		Dim s As New Stock
		s.ID = "A-" & iCounter
		StockArray.Add(s)
		ListStock()
	End Sub
	Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
		iCounter = iCounter + 1
		Dim s As New Stock
		s.ID = "B-" & iCounter
		StockArray.Add(s)
		ListStock()
	End Sub
	Private Sub ListStock()
		Dim s As Stock, msg As String = ""
		For Each s In StockArray
			msg = msg & s.ID & ", "
		Next
		msg = Strings.Left(msg, Len(msg) - 2)
		MsgBox("ArrayList contains " & msg)
	End Sub
End Class
Public Class Stock
	Public ID As String
End Class

[channaJ]

I have an arraylist and i define it as public variable

Public StockArray As New ArrayList

inside button1_click body
i append new elements in that Stockarray
by
dim stockobj as new stock // stock is a class

StockArray.Add( stockobj)

when i print any element of Stockarray within button1 body it works fine

but when i call the stockArray in a another button body the StockArray is empty !


any ideas will be Extremly helpful

Hi,

Is it a web application you are working on? If it is so, I think the problem is caused by the postback. When you do a postback from the first button click,

Public StockArray As New ArrayList

will be called again and it will create a new empty StockArray object. You can use the following code to instanciate the StockArray only in the initial page load.

if(!IsPostback)
Public StockArray As New ArrayList

Hope this will help.

[nadaNuaim]

thanks alot SammyB but this is exactly my problem the buttons ommit each other changes


and YES channaJ i'm using a web application i'm interested in your sollution

but shall I declare StockArray only once in the page_load ? because when I did the buttons could not see StockArray declaration!

and it force me to replace

 
If (Not IsPostBack) Then
Public StockArray as new ArrayList 
End IF

with this

 
If (Not IsPostBack) Then
Dim StockArray as new ArrayList 
End IF

and when I declare StockArray inside the body of Page_Load and inside the body of page Class the Array became empty :)

I'm So sorry but I'm new to asp.net with VB

[SammyB]

> I'm So sorry but I'm new to asp.net with VB
You are better than I, I've never created a web form, so Chan will have to help you there.

But, notice where I defined StockArray. It is inside the Form class, but outside of all of the Sub's. Thus, there is just one of them and all of the Sub's can access it. You should have a similar structure in your code.

[nadaNuaim]

Hi,

Is it a web application you are working on? If it is so, I think the problem is caused by the postback. When you do a postback from the first button click,

Public StockArray As New ArrayList

will be called again and it will create a new empty StockArray object. You can use the following code to instanciate the StockArray only in the initial page load.

if(!IsPostback)
Public StockArray As New ArrayList

Hope this will help.

*************** ********
Hello channaJ,

I did exactly what you siad but declaring StockArray as an ArrayList inside the page_load makes StockArray undeclared to other subs inside the page calss

as you siad when not post back the array contents will be empty ,i checked that by printing the array count (StockArray.Cou nt) and the result is zero :(

what should i do i need the array to save pervious valuse of stocks and use them when Undoing last changes.

thanks in advance

[nadaNuaim]

Hello every body

can any one help me with this issue i waste lots of time on it but still could not find the right sullotion any ideas :) !

regards

[Frinavale]

I have an arraylist and i define it as public variable

Public StockArray As New ArrayList

inside button1_click body
i append new elements in that Stockarray
by
dim stockobj as new stock // stock is a class

StockArray.Add( stockobj)

when i print any element of Stockarray within button1 body it works fine

but when i call the stockArray in a another button body the StockArray is empty !


any ideas will be Extremly helpful

Hi there!

When creating a web application you have to remember that every time the user clicks a button (or causes a postback event) its as if they are coming to the website for the first time.

In your case, you're creating the stockArray ArrayList, but you are only filling it within the method that handles your button click event. Once that information is sent back to the user, all the objects are destroyed.

There is never a persistent connection to the user and the application.

This means that when the user does something else that causes a postback a new stockArray (ArrayList) is created.

In order to use information collected from a previous postback to the website you need to store your arrayList in a persistent data store....like Session.

(please note that my code is in VB.NET and is just a guideline...it probably wont work)

Private stockArray As ArrayList

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

    'Since this is executed first every time we fill our stockArray 
    'variable with what ever is in the Session from previous visits
    'this way we can use it in the subs that handle the events

    stockArray = new ArrayList

    Try
        stockArray=CType(Session("arrayListInStore"),ArrayList)

        If stockArray Is Nothing
             'This is the case when the user is first visiting the website or the
             'Session has expired and there is no arrayList stored in session
   
            stockArray = new ArrayList
   
             'here fill your stock array with default values if you'd like
        End If
     Catch ex As Exception

     End Try

End Sub

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    'Here you can fill the stockArray Array list but make sure that you
    'Store this in session so that you can use this data later

     'I always double check to make sure the object has been intialized
      If stockArray Is Nothing Then
        stockArray = new ArrayList
     End IF

     stockArray.Add(....)
    Session("arrayListInStore")=stockArray

End Sub


Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    'Since you've already filled the stockArray variable in the page_load method
    'with the information gathered during the Button1 postback (which was 
    'stored in session)...
    'You will be able to use the information in the stockArray variable in
    'this method

     lbl_output.Text = stockArray.Length.ToString()

End Sub

Does this make sense?

(Oh yeah, you don't need to make the variable Public unless its being used by another object. I'd recommend making it Private if its not being used by another object)

Cheers

-Frinny

[nadaNuaim]

pew! Finally i found it instead of declaring StockArray as public or dim declare it as shared
thanks Chan and Sammy for your time and effort :)

here is the code

 

    Shared StockArray As New ArrayList

 '***********************************************************'
    Public Sub Update_Group(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
        'Loop through each DataGridItem, and determine which CheckBox controls
        'have been selected.


        Dim GridItem As DataGridItem
        For Each GridItem In DataGrid1.Items

            Dim myCheckbox As CheckBox = CType(GridItem.Cells(0).Controls(1), CheckBox)
            Dim TextBox1 As TextBox = CType(GridItem.Cells(4).Controls(1), TextBox)
            Dim TextBox2 As TextBox = CType(GridItem.Cells(5).Controls(1), TextBox)

            If myCheckbox.Checked = True Then

                Dim Stockobj As New stock
                Stockobj.FunCode = DataGrid1.DataKeys(GridItem.ItemIndex).ToString()
                Stockobj.FunPrice = Convert.ToDouble(TextBox1.Text)
                Stockobj.FunVolume = Convert.ToInt64(TextBox2.Text)
                StockArray.Add(Stockobj)
                '  Response.Write(Stockobj.FunCode)
                ' rowCount += 1
                DoUpdateStock(DataGrid1.DataKeys(GridItem.ItemIndex).ToString(), Convert.ToDouble(TextBox1.Text), Convert.ToInt64(TextBox2.Text))
            End If
        Next
        updateDate.Text = "Last Update was on " & Now()


        BindDataGrid()
    End Sub



    Public Sub Undo_Update(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button3.Click

        Dim i As Integer = 0

        While (i < StockArray.Count - 1)
        
            DoUpdateStock(StockArray(i).FunCode, StockArray(i).FunPrice, StockArray(i).FunVolume)
            i += 1
        End While

        updateDate.Visible = False

        BindDataGrid()

    End Sub

[nadaNuaim]

Hi there!

When creating a web application you have to remember that every time the user clicks a button (or causes a postback event) its as if they are coming to the website for the first time.

In your case, you're creating the stockArray ArrayList, but you are only filling it within the method that handles your button click event. Once that information is sent back to the user, all the objects are destroyed.

There is never a persistent connection to the user and the application.

This means that when the user does something else that causes a postback a new stockArray (ArrayList) is created.

In order to use information collected from a previous postback to the website you need to store your arrayList in a persistent data store....like Session.

(please note that my code is in VB.NET and is just a guideline...it probably wont work)

Private stockArray As ArrayList

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

    'Since this is executed first every time we fill our stockArray 
    'variable with what ever is in the Session from previous visits
    'this way we can use it in the subs that handle the events

    stockArray = new ArrayList

    Try
        stockArray=CType(Session("arrayListInStore"),ArrayList)

        If stockArray Is Nothing
             'This is the case when the user is first visiting the website or the
             'Session has expired and there is no arrayList stored in session
   
            stockArray = new ArrayList
   
             'here fill your stock array with default values if you'd like
        End If
     Catch ex As Exception

     End Try

End Sub

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    'Here you can fill the stockArray Array list but make sure that you
    'Store this in session so that you can use this data later

     'I always double check to make sure the object has been intialized
      If stockArray Is Nothing Then
        stockArray = new ArrayList
     End IF

     stockArray.Add(....)
    Session("arrayListInStore")=stockArray

End Sub


Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    'Since you've already filled the stockArray variable in the page_load method
    'with the information gathered during the Button1 postback (which was 
    'stored in session)...
    'You will be able to use the information in the stockArray variable in
    'this method

     lbl_output.Text = stockArray.Length.ToString()

End Sub

Does this make sense?

(Oh yeah, you don't need to make the variable Public unless its being used by another object. I'd recommend making it Private if its not being used by another object)

Cheers

-Frinny

--------------------------

Hi Firnny

you know i have read lots of articles talking about session I'll try your code coze the code i have solves some problems not all of them

thanks