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Adrian Hernando Solanas
Asked: 2020-04-10 15:44:32 +0800 CST 2020-04-10 15:44:32 +0800 CST

Object reference not set to an instance of an object. VB.NET

  • 772

I am trying to launch a command from this class:

Imports System.Data.OleDb
Imports System.IO

Public Class GestionSql
    Private sReturn As String = ""
    Private sConection As String = "Provider=Microsoft.Jet.OLEDB.4.0; Data Source=" +Directory.GetCurrentDirectory() + "\TPV.mdb;"
    Private oConection As OleDb Connection
    Public oCommand As New OleDbCommand

    Public Function Launch(ByVal value As String) As String
        Try
            oConection.Open()
            oConection = New OleDbConnection(sConection)
            oCommand.CommandText = Value
            sReturn = oCommand.ExecuteNonQuery()
            oConection.Close()
            MessageBox.Show("La contraseña es: " + sReturn.ToString)
        Catch ex As Exception
            MessageBox.Show(ex.ToString)
        End Try
        Return sReturn
    End Function
End Class

In this class:

Public Class IDVendedor
    Private GestionSql As New GestionSql
    Private sCmd As String
    Private sPass As String

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        'Montamos y lanzamos el comando
        sCmd = "SELECT Password FROM Vendedores WHERE Id=" + id.Text
        sPass = GestionSql.Launch(sCmd)
    End Sub
End Class

I get the error:

Object reference not set to an instance of an object. It tells me that the error is in ExecuteNonQuery in the sCmd parameter.

vb.net

3 Answers

  1. Best Answer

    The error Referencia a objeto no establecida como instancia de un objetowill accompany you for many years in the world of programming, but soon you will get used to knowing immediately where the error is :)

    What does that message mean?

    You are reading a property or executing a function from an object variable ("object reference") that has not been initialized ("not set to an instance of an object"). That is, you declared a variable and used it without first assigning it a value.

    The error appears on line 15 of your capture, because you have reversed the initialization of the variable oConexion(line 16) and the first use (line 15):

    oConection.open()
oConection = New OleDbConnection(sConection)

    To solve you just have to initialize the variable oConexionbefore opening the connection:

    oConection = New OleDbConnection(sConection) 
oConection.open()
    • 2

  2. In the code I see you are trying to use oConnection before initializing it, in theory your problem could be solved by changing this:

        oConection.Open()
    oConection = New OleDbConnection(sConection)

    For this:

        oConection = New OleDbConnection(sConection)//primero creas el objeto
    oConection.Open()//despues lo utilizas

    Explanation: oConectionit is the same nullas being nullor not being initialized, you cannot access its methods or attributes, so before calling .open()you need to assign a value to it when using =newcreate a new instance of this object and this is how you avoid the Object not error initialized .

    What I see is that you need to initialize oConnection, but you would have to validate it, check the image to see if it can help you in any way.

    enter image description here

    • 2

  3. In the end I solved it in the following way:

    Imports System.Data.OleDb
Imports System.IO

Public Class GestionSql
Private sReturn As String = ""
Private sConection As String = "Provider=Microsoft.Jet.OLEDB.4.0; Data Source=" + Directory.GetCurrentDirectory() + "\TPV.mdb;"
Private oConection As New OleDbConnection(sConection)
Public oCommand As New OleDbCommand
'Protected daAdapter As New SqlDataAdapter(sCmd, oConection)
'Protected dsDataSet As New DataSet

'Lanzar comandos con respuesta (SELECT)
Public Function Launch(ByVal value As String) As String
    Try
        oConection.Open()
        oCommand.CommandText = value
        oCommand.CommandType = CommandType.Text
        oCommand.Connection = oConection
        sReturn = oCommand.ExecuteScalar()
        oConection.Close()
        MessageBox.Show("La contraseña es: " + sReturn.ToString)
    Catch ex As Exception
        MessageBox.Show(ex.ToString)
    End Try
    Return sReturn
End Function
End Class
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