Member Avatar for lanitooot

help guys. im having this error.. i don't know hat to do.. please help..thankss

#Region "FillListView"

Sub FillListview()
lvList.Items.Clear()
sqlQry = "SELECT * from book ORDER BY book_id ASC"
Dim mycmd As New MySqlCommand(sqlQry, myConn)
Dim dReader As MySqlDataReader = mycmd.ExecuteReader() <----
this is the error im getting it says invalid operation exception was unhandled and must be open and valid --->

While dReader.Read()
With lvList
.Items.Add(dReader("book_id"))
With .Items(.Items.Count - 1).SubItems
.Add(dReader("book_title"))
.Add(dReader("book_author"))
.Add(dReader("book_publisher"))
.Add(dReader("isbn"))
.Add(dReader("call_no"))
End With
End With
End While
dReader.Close()
End Sub
#End Region

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  • Latest Post Latest Post by AndreRet

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Member Avatar for AndreRet

Dim dReader As MySqlDataReader = mycmd.ExecuteReader()

It seems that your reader is from a class module. It is either not open in the context you have shown, so it can not execute any operations. Post us the code under the MySqlDataReader. This might show us why there is no connection.

Member Avatar for lanitooot 
this is the whole code of the bookform: ***************************************************************************** Imports MySql.Data.MySqlClient Public Class bookForm Dim myConn As New MySqlConnection Dim sqlQry As String = Nothing Dim mycmd As New MySqlCommand Dim dReader As MySqlDataReader 'Dim dAdap As New MySqlDataAdapter 'Dim dSet As New DataSet Dim connString As String Dim str As String = Nothing Private Sub bookForm_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load 
        Call FillListview()
        Call LVsettings()
        Call ConnToDB()
        Call FillListview()
        Call Set1() End Sub #Region "FillListView" Sub FillListview()
        lvList.Items.Clear()
        sqlQry = "SELECT * from book ORDER BY book_id ASC"
        mycmd = New MySqlCommand(sqlQry, myConn)
        myConn.Open()
        dReader = mycmd.ExecuteReader 
        While dReader.Read
        With lvList
        .Items.Add(dReader("book_id"))
        With .Items(.Items.Count - 1).SubItems
        .Add(dReader("book_title"))
        .Add(dReader("book_author"))
        .Add(dReader("book_publisher"))
        .Add(dReader("isbn"))
        .Add(dReader("call_no"))
        End With
        End With
        End While
        dReader.Close()
        myConn.Close() End Sub #End Region #Region "Connection" Sub ConnToDB()
        Try
        With myConn
        If .State = ConnectionState.Open Then .Close()
        .ConnectionString = "datasource=localhost; username=root; password=lani; database=admin"
        .Open()
        End With
        Catch ex As Exception
        MessageBox.Show("Unable to connect", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
        Application.Exit()
        End Try End Sub #End Region #Region "LVSettings" Sub LVsettings()
        With lvList.Columns
        .Add("book_id", 50, HorizontalAlignment.Left)
        .Add("book_title", 200, HorizontalAlignment.Left)
        .Add("book_author", 200, HorizontalAlignment.Left)
        .Add("isbn", 100, HorizontalAlignment.Left)
        .Add("call_no", 100, HorizontalAlignment.Left)
        End With End Sub #End Region #Region "object Settings " Sub Set1()
        cmdAdd.Enabled = True
        cmdEdit.Enabled = True
        cmddelete.Enabled = True
        cmdExit.Enabled = True 
        cmdsave.Enabled = False
        cmdCancel.Enabled = False
        Dim txt As Control
        For Each txt In Me.Controls
        If TypeOf txt Is TextBox Then
        txt.Enabled = False
        End If
        Next 
        lvList.Enabled = True End Sub Sub Set2()
        cmdAdd.Enabled = False
        cmdEdit.Enabled = False
        cmddelete.Enabled = False
        cmdExit.Enabled = False 
        cmdsave.Enabled = True
        cmdCancel.Enabled = True 
        Dim txt As Control
        For Each txt In Me.Controls
        If TypeOf txt Is TextBox Then
        txt.Enabled = True
        End If
        Next
        lvList.Enabled = False End Sub #End Region #Region "CLEAR TEXTBOX" Sub ClearAlltextBox()
        Dim a As Control
        For Each a In Me.Controls
        If TypeOf a Is TextBox Then
        a.Text = Nothing
        End If
        Next End Sub #End Region Private Sub cmdAdd_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdAdd.Click
        str = "add"
        Call Set2()
        Call ClearAlltextBox()
        idtxt.Text = "Computer Generated"
        idtxt.Enabled = False End Sub Private Sub cmdCancel_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdCancel.Click
        myConn.Close()
        Me.Close()
        Call Set1()
        Call ClearAlltextBox() End Sub Private Sub cmdEdit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdEdit.Click
        If idtxt.Text = "" Then
        MessageBox.Show("Please Select Record to Update", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
        Else
        str = "edit"
        Call Set2()
        idtxt.Enabled = False
        End If End Sub Private Sub cmdExit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdExit.Click
        Application.Exit() End Sub Private Sub cmdsave_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdsave.Click
        If str = "add" Then
        ''''''ADD NEW RECORD'''''''
        If idtxt.Text = "" Or titletxt.Text = "" Or authortxt.Text = "" Or Pubtxt.Text = "" Or isbntxt.Text = "" Or calltxt.Text Then
        MessageBox.Show("All fields Are Required", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
        Else
        sqlQry = "INSERT INTO book(book_id,book_title,book_author,book_publisher,isbn,call_no) "
        sqlQry = sqlQry + "VALUES('" & idtxt.Text & "','" & titletxt.Text & "','" & authortxt.Text & "','" & Pubtxt.Text & "','" & isbntxt.Text & "','" & calltxt.Text & "')"
        mycmd = New MySqlCommand
        With mycmd
        .CommandText = sqlQry
        .Connection = myConn
        .ExecuteNonQuery()
        End With
        Call Set1()
        End If 
        Else
        ''''''''''UPDATE RECORD'''''''
        If idtxt.Text = "" Or titletxt.Text = "" Or authortxt.Text = "" Or Pubtxt.Text = "" Or isbntxt.Text = "" Or calltxt.Text Then
        MessageBox.Show("All fields Are Required", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
        Else
        sqlQry = "UPDATE book SET "
        sqlQry = sqlQry + " book_title = '" & titletxt.Text & "',"
        sqlQry = sqlQry + " book_author = '" & authortxt.Text & "',"
        sqlQry = sqlQry + " book_publisher = '" & Pubtxt.Text & "',"
        sqlQry = sqlQry + " isbn = '" & isbntxt.Text & "',"
        sqlQry = sqlQry + " call_no = '" & authortxt.Text & "'"
        sqlQry = sqlQry + " WHERE "
        sqlQry = sqlQry + " book_id = " & idtxt.Text 
        mycmd = New MySqlCommand(sqlQry, myConn)
        mycmd.ExecuteNonQuery()
        Call Set1()
        End If
        End If 
        Call FillListview()
        Call ClearAlltextBox() End Sub Private Sub cmddelete_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmddelete.Click
        If MsgBox("Are you sure you want to delete this record?", MsgBoxStyle.Question + MsgBoxStyle.YesNo) = MsgBoxResult.Yes Then
        sqlQry = "DELETE FROM book WHERE book_id = " & idtxt.Text
        mycmd = New MySqlCommand(sqlQry, myConn)
        mycmd.ExecuteNonQuery()
        End If
        Call ClearAlltextBox()
        Call FillListview() End Sub Private Sub lvList_SelectedIndexChanged_1(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles lvList.SelectedIndexChanged
        If lvList.SelectedItems.Count > 0 Then
        With lvList.SelectedItems(0)
        idtxt.Text = .Text
        titletxt.Text = .SubItems(1).Text
        authortxt.Text = .SubItems(2).Text
        Pubtxt.Text = .SubItems(3).Text
        isbntxt.Text = .SubItems(4).Text
        calltxt.Text = .SubItems(5).Text
        End With
        End If End Sub End Class
Member Avatar for lanitooot

i put myconn.open as shown at line33 but an error occured and says: argument null exception was unhandled. key cannot be null


help i dont know what to do.. thanksss

Member Avatar for AndreRet

a Quick glance at your code seems fine. It is with your reader.

Dim dReader As MySqlDataReader = mycmd.ExecuteReader() <----
this is the error im getting it says invalid operation exception was unhandled and must be open and valid --->

Try and change MySqlDataReader line to the following -

Dim dReader As New MySqlDataReader
dReader = mycmd.ExecuteReader

, and see if it helps. I am assuming that MySqlDataReader is a foreign control which was referenced through references?

Member Avatar for lanitooot 
#Region "FillListView" Sub FillListview()
        lvList.Items.Clear()
        sqlQry = "SELECT * from book ORDER BY book_id ASC"
        Dim mycmd As New MySqlCommand(sqlQry, myConn)
        Try
        myConn.Open()
        Dim dReader As MySqlDataReader
        dReader = mycmd.ExecuteReader
        While dReader.Read()
        With lvList
        .Items.Add(dReader("book_id"))
        With .Items(.Items.Count - 1).SubItems
        .Add(dReader("book_title"))
        .Add(dReader("book_author"))
        .Add(dReader("book_publisher"))
        .Add(dReader("isbn"))
        .Add(dReader("call_no"))
        End With
        End With
        End While
        dReader.Close()
        myConn.Close()
        Catch ex As MySqlException
        End Try End Sub #End Region

yes i tried what you said as shown above. but when i put the myconn.open its saying the 'null reference exception was unhandled' object reference not set to an instance of an object

im researching and debugging this error for a while now.. just cant figure it out yet.. can you please help me again :D thanksss much

Edited by lanitooot because: n/a
Member Avatar for AndreRet

That is it seems because you are trying to open 'myConn' without setting a reference to it -

Dim mycmd As New MySqlCommand(sqlQry, myConn)
Try
myConn.Open()

Set a reference to myConn ABOVE this code as you did with sqlQry and see if that works.

Member Avatar for lanitooot

whew!.. it worked..i hav tried try and catch method maybe i dont know wer to put it thenn.. now it worked..thanks much andreret

Member Avatar for AndreRet

Only a pleasure. If you have any more problems, please post it under .Net for us, seeing that you are using .Net. Thanks man, and happy coding.

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