Visual Basic

Re: object reference not set to an instance of an object error

22-Jul-06 4:11

I am getting this error when I run the program. I am not sure how to fix this error, if anybody can help me I will appreciate it. The program has two forms. Form1 has the search textbox and form2 takes the information from form1 and populates form2. I have attached the code for both forms, so you can see what I am talking about. Any help will be appreciated. Thanks

Form1 Code:

 Private Sub btnSearch_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSearch.Click<br />
        Dim oForm2Data As New Form2.Form2Data(Me.txtbarcodeid.Text)<br />
<br />
        If oForm2Data.HasData Then<br />
<br />
            Form2.Initialize(Me, oForm2Data)<br />
<br />
        Else<br />
            ' The Data does not exists for the item in the textbox<br />
<br />
        End If<br />
    End Sub<br />

Form2 Code:

Dim dt As New DataTable<br />
    Dim sqlStr As String = "SELECT * FROM testbackup"<br />
    Dim sqlstr1 As String = "SELECT * FROM history"<br />
    Dim connstr As String = "Provider = Microsoft.Jet.OLEDB.4.0;" & _<br />
    "Data Source = backup.mdb"<br />
    Dim dataadapter As New OleDb.OleDbDataAdapter(sqlStr, connstr)<br />
<br />
    Public Shared Sub Initialize(ByVal Owner As IWin32Window, ByRef oForm2Data As Form2Data)<br />
        Dim result As DialogResult<br />
        Dim frm2 As New Form2<br />
<br />
        With frm2<br />
            'Using TheData Populate each Control on Form2<br />
        End With<br />
<br />
        Result = frm2.ShowDialog(Owner)<br />
<br />
        If Result = System.Windows.Forms.DialogResult.OK Then<br />
<br />
<br />
            With frm2<br />
                'Now update the values in TheData with its value in its Form2 Control<br />
            End With<br />
<br />
            'Save Changes<br />
            oForm2Data.SaveData()<br />
        End If<br />
<br />
    End Sub<br />
<br />
    Public Class Form2Data<br />
        Public HasData As Boolean<br />
        Public TheData As DataRow<br />
<br />
        Public Sub New(ByVal Value As String)<br />
            Dim dsData As DataSet<br />
            Dim stSQL As String<br />
<br />
            stSQL = "Select * from testbackup Where barcodeid = '" & Value & "'"<br />
<br />
            'Database code to return dataset to dsData<br />
<br />
<br />
            Select Case dsData.Tables(0).Rows.Count<br />
                Case 1 'One Row Returned<br />
                    HasData = True<br />
                    TheData = dsData.Tables(0).Rows(0)<br />
                Case 0 'No Rows Found<br />
                    HasData = False<br />
                    TheData = Nothing<br />
                Case Else 'More then one row returned<br />
                    'Decided how to handle<br />
                    HasData = True<br />
                    TheData = dsData.Tables(0).Rows(0)<br />
            End Select<br />
<br />
<br />
        End Sub<br />
<br />
        Public Sub SaveData()<br />
            'Routine to save the data<br />
        End Sub

mr_lasseter22-Jul-06 4:47

Re: object reference not set to an instance of an object error

22-Jul-06 4:47

Where is the exception being thrown?

Mike Lasseter

str5022-Jul-06 4:58

Re: object reference not set to an instance of an object error

22-Jul-06 4:58

at this statement

Select Case dsData.Tables(0).Rows.Count

mr_lasseter22-Jul-06 5:08

Re: object reference not set to an instance of an object error

22-Jul-06 5:08

I don't see where dsData is getting Initialized. Is your database code working?

Mike Lasseter

str5022-Jul-06 5:21

Re: object reference not set to an instance of an object error

22-Jul-06 5:21

which database code. I am not sure which one. I wanted to post my program here, but I don't know how to do that. Can you tell me where to initialize my dsdata

mr_lasseter22-Jul-06 5:32

Re: object reference not set to an instance of an object error

22-Jul-06 5:32

<br />
Dim dsData As DataSet  '--THIS VARIABLE IS NOT GETTING INITIALIZED/SET<br />
Dim stSQL As String<br />
<br />
stSQL = "Select * from testbackup Where barcodeid = '" & Value & "'"<br />
<br />
'THIS IS DB CODE I AM TALKING ABOUT<br />
'Database code to return dataset to dsData<br />
<br />

Without seeing the code I can't say exactly where your problem is, but here are some things to check.
1. Is the dsData nothing when you step through your code?
2. If not does it contain any tables?

My guess is the dsData is not getting populated correctly in the Database Code

Mike Lasseter

str5022-Jul-06 6:03

Re: object reference not set to an instance of an object error

22-Jul-06 6:03

can i e-mail you my program, so you can see what is happening. let me know. thanks for your help so far

mr_lasseter22-Jul-06 6:18

Re: object reference not set to an instance of an object error

22-Jul-06 6:18

Just post the code for 'Database code to return dataset to dsData in the forum. It shouldn't be that long.

Mike Lasseter

str5022-Jul-06 7:42

Re: object reference not set to an instance of an object error

22-Jul-06 7:42

I am not sure what to put in that area. Would you be able to help me with that if you don't mind. thanks

mr_lasseter22-Jul-06 10:34

Re: object reference not set to an instance of an object error [modified]

22-Jul-06 10:34

That is what is giving you your problem. Try looking at the following link.

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpguide/html/cpconcreatingusingdatasets.asp[^]

Mike Lasseter

str5022-Jul-06 10:52

Re: object reference not set to an instance of an object error

22-Jul-06 10:52

Alright I looked at the website and this is what I got out of it. This is what I have so far, but when I run the program now I don't get anything. It does not go to form2. It just stays at form1 even when I hit the search button. I must have done something wrong and I can't figure out. I am trying my best to figure out. Any help will be appreciated. Thanks again

Public Sub New(ByVal Value As String)<br />
            Dim dsData As DataSet = New DataSet("BackupInfo")<br />
            Dim stSQL As String<br />
            Dim backupTable As DataTable = dsData.Tables.Add("testbackup")<br />
<br />
            stSQL = "Select * from testbackup Where barcodeid = '" & Value & "'"<br />
<br />
            'Database code to return dataset to dsData<br />
<br />
<br />
            backupTable.Columns.Add("Barcodeid", Type.GetType("System.Int32"))<br />
            backupTable.Columns.Add("location", Type.GetType("System.Int32"))<br />
            backupTable.Columns.Add("datein", Type.GetType("System.String"))<br />
            backupTable.Columns.Add("dateout", Type.GetType("System.String"))<br />
            backupTable.Columns.Add("timein", Type.GetType("System.String"))<br />
            backupTable.Columns.Add("timeout", Type.GetType("System.String"))<br />
            backupTable.Columns.Add("comment", Type.GetType("System.String"))<br />
<br />
            Select Case dsData.Tables(0).Rows.Count<br />
                Case 1 'One Row Returned<br />
                    HasData = True<br />
                    TheData = dsData.Tables(0).Rows(0)<br />
                Case 0 'No Rows Found<br />
                    HasData = False<br />
                    TheData = Nothing<br />
                Case Else 'More then one row returned<br />
                    'Decided how to handle<br />
                    HasData = True<br />
                    TheData = dsData.Tables(0).Rows(0)<br />
            End Select<br />
<br />
<br />
        End Sub

-- modified at 16:57 Saturday 22nd July, 2006

mr_lasseter23-Jul-06 5:49

Re: object reference not set to an instance of an object error

23-Jul-06 5:49

You need to fill the dataset with the data from the database. Look at the link below.

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpguide/html/cpconpopulatingdatasetfromdataadapter.asp[^]

Mike Lasseter

str5023-Jul-06 12:06

Re: object reference not set to an instance of an object error [modified]

23-Jul-06 12:06

Alright. I finally made progress with your help. thanks a lot. But now when I run the program I get the message that I put in "not valid". It is not picking up the record. This is the code I have so far. Any help will be appreciated. Thanks

Public Sub New(ByVal Value As String)<br />
            Dim dsData As DataSet = New DataSet1<br />
            Dim stSQL As String<br />
            Dim backupTable As DataTable = dsData.Tables.Add("testbackup")<br />
<br />
            stSQL = "Select * from testbackup Where barcodeid = '" & Value & "'"<br />
<br />
            'Database code to return dataset to dsData<br />
<br />
<br />
            Dim orderConn As OleDb.OleDbConnection = New OleDb.OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;" & _<br />
                                                       "Data Source=backup.mdb;")<br />
            Dim orderDA As OleDb.OleDbDataAdapter = New OleDb.OleDbDataAdapter("SELECT * FROM testbackup", orderConn)<br />
<br />
           <br />
            orderConn.Open()<br />
<br />
            Dim custDS As DataSet = New DataSet<br />
<br />
           <br />
            orderDA.Fill(custDS, "testbackup")<br />
<br />
            orderConn.Close()<br />
<br />
            backupTable.Columns.Add("Barcodeid", Type.GetType("System.Int32"))<br />
            backupTable.Columns.Add("location", Type.GetType("System.String"))<br />
            backupTable.Columns.Add("datein", Type.GetType("System.String"))<br />
            backupTable.Columns.Add("dateout", Type.GetType("System.String"))<br />
            backupTable.Columns.Add("timein", Type.GetType("System.String"))<br />
            backupTable.Columns.Add("timeout", Type.GetType("System.String"))<br />
            backupTable.Columns.Add("comment", Type.GetType("System.String"))<br />
<br />
            Select Case dsData.Tables(0).Rows.Count<br />
                Case 1 'One Row Returned<br />
                    HasData = True<br />
                    TheData = dsData.Tables(0).Rows(0)<br />
                Case 0 'No Rows Found<br />
                    HasData = False<br />
                    TheData = Nothing<br />
                Case Else 'More then one row returned<br />
                    'Decided how to handle<br />
                    HasData = True<br />
                    TheData = dsData.Tables(0).Rows(0)<br />
            End Select<br />
<br />
<br />
        End Sub

This is the code where it says not value.

Private Sub btnSearch_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSearch.Click<br />
        Dim oForm2Data As New Form2.Form2Data(Me.txtbarcodeid.Text)<br />
<br />
        If oForm2Data.HasData Then<br />
<br />
            Form2.Initialize(Me, oForm2Data)<br />
<br />
        Else<br />
            ' The Data does not exists for the item in the textbox<br />
            MsgBox("Not valid")<br />
        End If<br />
    End Sub

xivovivovix4-Aug-06 1:42

xivovivovix

4-Aug-06 1:42

i have experienced like this one too.
the problem was the data type. How come???
let see your code below :

stSQL = "Select * from testbackup Where barcodeid = '" & Value & "'"

if we see at barcodeid = '" & Value & "'" , we can say that barcodeid is string data type.
But it's possible in your datasource, the barcodeid is integer..

so the solution is remove ' charachters, and it will be like this:

stSQL = "Select * from testbackup Where barcodeid = " & Value

-- modified at 7:43 Friday 4th August, 2006

Hard disk serial number

mayoush22-Jul-06 3:17

mayoush

22-Jul-06 3:17

hiiii all
please i need to find the hard disk (volume) serial number,
the number that is given to the hard disk from manufacturer not the one that changes after formating the hard disk.
can anyone help me to this in VB.Net please Cry | :((

mayoush

bob1697222-Jul-06 8:07

bob16972

22-Jul-06 8:07

Windows Management Instrumentation (WMI)

_mubashir22-Jul-06 8:59

_mubashir

22-Jul-06 8:59

You can also try this code

<br />
Dim moReturn As Management.ManagementObjectCollection<br />
Dim moSearch As Management.ManagementObjectSearcher<br />
Dim mo As Management.ManagementObject<br />
moSearch = New Management.ManagementObjectSearcher("Select * from Win32_PhysicalMedia")<br />
moReturn = moSearch.Get<br />
For Each mo In moReturn<br />
   MsgBox(Trim(mo("SerialNumber")))<br />
Next<br />

regards
Mubashir

mayoush23-Jul-06 4:35

mayoush

23-Jul-06 4:35

hi thx for your help,
but the VB.Net didn't recognize the "Management.ManagementObjectCollection"
do i need to import anything for it to work?
thx again for your help;)
i do Appritiate it Smile | :)

Chatura Dilan23-Jul-06 15:40

Chatura Dilan

23-Jul-06 15:40

You need to import System.Management
You have to select
Project Menu --> Add Reference --> .NET tab --> System.Manegement

Regards,

Chatura Dilan