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Apr 21st, 2012, 05:03 PM
#1
Thread Starter
New Member
[RESOLVED] Object reference not set to an instance of an object.
When trying to display data from the database into my textboxes, this error keeps appearing: “Object reference not set to an instance of an object.”
I don’t know how to fix it, and not that fabulous at coding,so i know there is probably major issues, but i just want to know how to solve this problem first.
Code:
Public Class FrmTeach_SelectQuestions
Dim Inc As Integer
Dim MaxRows As Integer
Dim Teach_Question As New DataSet
Dim dsNewRow As DataRow
Dim SQL As String
Private Sub FrmTeach_SelectQuestions_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Teach_Question = DataBaseConnection.DBSelect("SELECT [QuestionText], [Unit], [A1], [A2], [A3], [A4], [CorrectAnswer] FROM [UnitQuestionsTable];")
MaxRows = Teach_Question.Tables("Results").Rows.Count
Inc = -1
DataBaseConnection.ResetDS()
Reset()
End Sub
Private Sub NavigateRecords()
TxbQuestionText.Text = Teach_Question.Tables("Results").Rows(Inc).Item(1)
TxbA1.Text = Teach_Question.Tables("Results").Rows(Inc).Item(3)
TxbA2.Text = Teach_Question.Tables("Results").Rows(Inc).Item(4)
TxbA3.Text = Teach_Question.Tables("Results").Rows(Inc).Item(5)
TxbA4.Text = Teach_Question.Tables("Results").Rows(Inc).Item(6)
End Sub
Private Sub BtnNext_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtnNext.Click
If Inc <> MaxRows - 1 Then
Inc = Inc + 1
NavigateRecords()
Else
MsgBox("...")
End If
End Sub
Private Sub BtnPrevious_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtnPrevious.Click
If Inc > 0 Then
Inc = Inc - 1
NavigateRecords()
ElseIf Inc = -1 Then
MsgBox("No Records Yet")
ElseIf Inc = 0 Then
MsgBox("First Record")
End If
End Sub
Private Sub BtnMoveLast_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtnMoveLast.Click
If Inc <> MaxRows - 1 Then
Inc = MaxRows - 1
NavigateRecords()
End If
End Sub
Private Sub BtnMoveFirst_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtnMoveFirst.Click
If Inc <> 0 Then
Inc = 0
NavigateRecords()
End If
End Sub
Private Sub BtnSave_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtnSave.Click
'Teach_Question.Tables("Results").Rows(Inc).Item(1) = TxbQuestionText.Text
SQL = "INSERT INTO UnitQuestionsTable ([QuestionText], [Unit], [A1], [A2], [A3], [A4], [CorrectAnswer]) " & "VALUES ('" & TxbQuestionText.Text & "', '" & CmbUnit.Text & "', '" & TxbA1.Text & "', '" & TxbA2.Text & "', '" & TxbA3.Text & "', '" & TxbA4.Text & "', '" & CmbCorrectAnswer.Text & "')"
DataBaseConnection.DBUpdate(SQL)
MsgBox("New Updates Saved.")
End Sub
Private Sub BtnAdd_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtnAdd.Click
If Inc <> -1 Then
dsNewRow = Teach_Question.Tables("Results").NewRow()
SQL = "INSERT INTO UnitQuestionsTable ([QuestionText], [Unit], [A1], [A2], [A3], [A4], [CorrectAnswer]) " & "VALUES ('" & TxbQuestionText.Text & "', '" & CmbUnit.Text & "', '" & TxbA1.Text & "', '" & TxbA2.Text & "', '" & TxbA3.Text & "', '" & TxbA4.Text & "', '" & CmbCorrectAnswer.Text & "')"
DataBaseConnection.DBUpdate(SQL)
Teach_Question.Tables("Results").Rows.Add(dsNewRow)
MsgBox("New Question Added To The Database")
End If
End Sub
End Class
Can anyone please try and help me fix it, thanks.
any additional information can be provided.
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Apr 21st, 2012, 08:39 PM
#2
Re: Object reference not set to an instance of an object.
Which line is causing the error? Also, what is "DataBaseConnection".
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Apr 21st, 2012, 10:17 PM
#3
Re: Object reference not set to an instance of an object.
When a NullReferenceException is thrown, it means that you tried to access a member of an object that doesn't exist. The first thing to do is to look at the call stack of the exception to see what line the exception was actually thrown on. If it was a line in your own code then the the IDE will have highlighted that line. If it was a line in compiled code then the IDE will have highlighted the last line of your own code that was executed. In the first case, which is the more likely, you simplay have to test the value of each reference on the line to see which one is Nothing. You can then work backwards to see where you expected a value to be assigned.
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Apr 22nd, 2012, 06:17 AM
#4
Thread Starter
New Member
Re: Object reference not set to an instance of an object.
the error appears here
Code:
TxbQuestionText.Text = Teach_Question.Tables("Results").Rows(Inc).Item(1)
database connection is the module used to connect to the database, i don't there is anything wrong there though
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Apr 22nd, 2012, 08:10 AM
#5
Re: Object reference not set to an instance of an object.
As I said, a NullReferenceException occurs when you try to access a member of an object that doesn't exist. As I also said, once you've identified the line the exception is thrown on, you simply need to determine which reference is Nothing. A reference is basically anything before a dot, because the dot is what you use to specify that you want to access a member. So, when the exception occurs, which reference on that line is Nothing? Once you've identified that, where did you expect a value to be assigned to that reference?
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Apr 23rd, 2012, 01:38 PM
#6
Thread Starter
New Member
Re: Object reference not set to an instance of an object.
Thanks, it works now
i had been using data set previously on another form, i guess i needed to reset the dataset.
i did this by placing the 'resets' before my command line
Code:
DataBaseConnection.ResetDS()
Reset()
Teach_Question = DataBaseConnection.DBSelect("SELECT [QuestionText], [Unit], [A1], [A2], [A3], [A4], [CorrectAnswer] FROM [UnitQuestionsTable];")
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