Object Reference not set to an instance of an object

[JohnOb]

Hi All,

I am in .NET 2003

 

I have a form and a toolbar on the form.

When the user clicks on a button on the toolbar I call

the following Sub

 

I get a crash on the last line: tlbSearch.Buttons(0).Enabled = True ' enable search

 

An unhandled exception of type "System.NullreferenceExecption" occured etc.....

Object Reference not set to an instance of an object

 

How can this be?, near the stop of the Sub I execute: tlbSearch.Buttons(0).Enabled = False ' Disable search

with no problem.

What could have happended to the toolbar object?

I am new to objects, I come from a VB background.

 

Thanks in Advance,

'-------------------------------------------------------------------

Public Sub DoTheSearch()

  Dim intDX As Integer
  Dim Structures As New clsStructures
  Dim clsMiscProjMulti As New     MiscProjectMultiTable_Handler(Permissions.ConnectionString)
  Dim SearchDataReader As SqlClient.SqlDataReader
  Dim blnWhere As Boolean = False
  Dim TheRetrievalType As RetrievalType
  Dim NotFoundMsg As String

  Dim strSelectString = "SELECT  ProjectID,Reg,Fee,Title," & _
                                 "MiscFeeTypeID," & _
                                 "Fee, Quarter, [Year],MiscProjectStatusID," & _
                                 "StatusDate,Miscellaneous_Project.Account_ID,FinalizedDate," & _
                                 "ContactEmployeeID,ContactEmail," & _
                                 "Unex_Employee.EmpFirstName + ' ' +  Unex_Employee.EmpLastName As EmpName," & _
                                 "Account.Exp_Account + '-' +  Account.Cost_Center As ExpAcctCC " & _
                         "FROM   Miscellaneous_Project " & _
                                 "Left Outer Join Unex_Employee " & _
                                 "On  Miscellaneous_Project.ContactEmployeeID = Unex_Employee.EmployeeID " & _
                                 "Left Outer Join Account " & _
                                 "On Miscellaneous_Project.Account_ID = Account.Account_ID "
  '----------

  Me.Cursor = System.Windows.Forms.Cursors.WaitCursor()
  
  tlbSearch.Buttons(0).Enabled = False                        ' Disable search - this is ok.
  menuSearch.Enabled = False

  tlbSearch.Buttons(1).Enabled = True                         ' Enable stop 
  menuStop.Enabled = True

  tlbSearch.Buttons(2).Enabled = False                        ' Disable print
  menuPrint.Enabled = False

  tlbSearch.Buttons(4).Enabled = False                        ' Disable the create new button. 
  menuCreateNew.Enabled = False                               ' Disable the create new menu item. 

  tlbSearch.Buttons(5).Enabled = False                        ' Disable Edit
  menuEdit.Enabled = False
  stsSearch.text = "Searching....."

  ' Clear the grid.

  C1FGResults.RowSel = -1
  C1FGResults.ColSel = -1

  If C1FGResults.Rows.Count > 1 Then

     For intDX = (C1FGResults.Rows.Count - 1) To 1 Step -1
         C1FGResults().Rows.Remove(intDX)
     Next

  End If

  '-----------------------------------------------

  If Me.txtRegProjID.Text = vbNullString Then

     ' look for projects using the type, Status and Deparatment
     ' build the query string, using the parameters.

     If c1cboFeeType.SelectedIndex > 0 Then
        strSelectString = strSelectString & " Where Miscellaneous_Project.MiscFeeTypeID = " & Structures.GetComboValue(c1cboFeeType)
        blnWhere = True
     End If

     '----------

     If c1cboProjectStatus.SelectedIndex > 0 Then

        If blnWhere = False Then
           strSelectString = strSelectString & " Where "
           blnWhere = True
        Else
           strSelectString = strSelectString & " And "
        End If

        strSelectString = strSelectString & "Miscellaneous_Project.MiscProjectStatusID = " & Structures.GetComboValue(c1cboProjectStatus)
     End If

     '----------

     If c1cboDept.SelectedIndex > 0 Then

        If blnWhere = False Then
           strSelectString = strSelectString & " Where "
           blnWhere = True
        Else
           strSelectString = strSelectString & " And "
        End If

        strSelectString = strSelectString & "Miscellaneous_Project.Account_ID = " & Structures.GetComboValue(c1cboDept)

     End If

     '----------

     If clsMiscProjMulti.dbSelect_DataReader(strSelectString, SearchDataReader) = True Then

        ' No errors, did we find any records?

        If SearchDataReader.HasRows = True Then

           While SearchDataReader.Read() = True
                 Call AddARow(SearchDataReader)
           End While
        Else
           Me.Cursor = System.Windows.Forms.Cursors.Default()
           MsgBox("Unable to find any projects with the parameters selected.", MsgBoxStyle.Information + MsgBoxStyle.OKOnly, "Not Found.")
        End If
     Else
        Me.Cursor = System.Windows.Forms.Cursors.Default()
        Dim err As New errorHandler(clsMiscProjMulti.lastException, "", True)
     End If

  Else

     ' Did the user enter a project Id or a Reg number? 

     If IsNumeric(Mid(txtRegProjID.Text, 1, 1)) Then
        strSelectString = strSelectString & " Where ProjectID = " & Trim$(txtRegProjID.Text)
        TheRetrievalType = RetrievalType.ProjectID
     Else
        ' the user entered a reg number. 
        strSelectString = strSelectString & " Where Reg = '" & Trim$(txtRegProjID.Text) & "'"
        TheRetrievalType = RetrievalType.RegNumber
     End If

     ' do the read.

     If clsMiscProjMulti.dbSelect_DataReader(strSelectString, SearchDataReader) = True Then

        ' No errors, did we find any records?

        If SearchDataReader.HasRows = True Then
           SearchDataReader.Read()
           Call AddARow(SearchDataReader)
        Else
           Me.Cursor = System.Windows.Forms.Cursors.Default()

           If TheRetrievalType = RetrievalType.ProjectID Then
              NotFoundMsg = "Project ID of : " & Trim$(txtRegProjID.Text)
           Else
              NotFoundMsg = "Reg Number of : " & Trim$(txtRegProjID.Text)
           End If

           MsgBox("Unable to find a project with a " & NotFoundMsg, MsgBoxStyle.Information + MsgBoxStyle.OKOnly, "Not Found.")
         End If

     Else
        Me.Cursor = System.Windows.Forms.Cursors.Default()
        Dim err As New errorHandler(clsMiscProjMulti.lastException, "", True)
     End If

  End If

  '-------------------------------------------------------

  Me.Cursor = System.Windows.Forms.Cursors.Default()

  ' the crash occurs on the next line. 

  tlbSearch.Buttons(0).Enabled = True                         ' Enable search

 

:confused:

Edited March 24, 2006 by PlausiblyDamp

[Cags]

It's quite difficult to understand a large block of code like that, especially without syntax highlighting. In future if you encase VB code in VB code tags it will help people read it. Looking at your code you don't seem to make it clear exactly where the trouble line occurs, if it occurs either after the button has been disposed or before it has been initialised this would cause that error.

Edit: My bad, it's all one continuous block of code isn't it. I was assuming that the '------ seperate the code functionally, whereas its just logically for the reader. Since this is the case I can't see any reason it would have been disposed by this point. Are you certain it's that line of code causing the null reference exception not the following one?

Edited March 24, 2006 by Cags

[PlausiblyDamp]

If you put a breakpoint on the line where the crash occurs what are the values for tlbSearch and tlbSearch.Buttons(0)?

[JohnOb]

The tlbsearch.buttons.count is zero.

 

How can this be? I am used to VB, not .NET

Do I have to declare and substantiate the toolbar everytime

I refer to a property on it?

 

 

 

:confused:

[Nerseus]

You said it doesn't blow up at the top, when you first reference tlbSearch.Buttons(0) so something must be clearing that collection. I'd step through code to find out when it's getting cleared.

 

-ner

[JohnOb]

Thank you for advice, I steped through the code and found out I was

doing something in one of the procs to cause the form to be unloaded,

(closed), that in turn was causing the toolbar buttons object collection to not exist.

 

Thanks Again,

 

John

 

You said it doesn't blow up at the top, when you first reference tlbSearch.Buttons(0) so something must be clearing that collection. I'd step through code to find out when it's getting cleared.

 

-ner

:)