Question

I’m getting an error in this code that says: object reference not set to an instance of an object.

Private Sub frmAdd_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

    con.ConnectionString = strcon

    con.Open()

con.ConnectionString = strcon

How can I fix this error?

Answer 1

That means that you are using a variable that is null (it’s not set to point to an instance of any object). In this case, con must be null, so you need to check if it’s null, and if so, then set it to a new object. For instance:

If con Is Nothing Then
    con = New OleDbConnection()  ' Or whatever type it is...
End If
con.ConnectionString = strcon
con.Open()

Or, better yet, just set it to a new object when you declare the variable, if that’s appropriate, for instance:

Dim conn As New OleDbConnection()

However, as Tim pointed out, it’s best to create a new connection each time you need one, and then you can use a Using block which will properly dispose of the object every time:

Using con As New OleDbConnection(strcon)
    con.Open()
    ' Use the connection ...
End Using