Question

i got this problem while trying to compile this code

Public Class Form2
Dim db_classobj As Object
Dim textboxobj() As TextBox = {TextBox1, TextBox2}
Dim datagridobj() As DataGridView = {DataGridView1}

Dim temp As New db_class(textboxobj, datagridobj, "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=datamhs.accdb", "mhs", "ksmhs")


Private Sub Form2_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
   db_classobj = temp
End Sub


End Class

while its compiling, i got this error message :

An error occurred creating the form. See Exception.InnerException for details. The error is: Object reference not set to an instance of an object.

whats wrong with my code? can someone fix it? i really appreciate it.
thanks.

Answer 1

Change your form load function to this, and remove the textboxobj, datagridobj, and temp declarations from the top of the class.

Private Sub Form2_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

     Dim textboxobj() As TextBox = {TextBox1, TextBox2}
     Dim datagridobj() As DataGridView = {DataGridView1}
     Dim temp As New db_class(textboxobj, datagridobj, "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=datamhs.accdb", "mhs", "ksmhs")
     db_classobj = temp
End Sub

Basically what was happening was that because your Dim temp as New statement was right in the class, it was being executed before the forms constructor, and the constructor is where all your controls (like TextBox1) get assigned their values, so basically you were passing an array of Nothing values to your db_class constructor. When you hit this line, _textbox(i).DataBindings.Add("text", ds.Tables(_mailboxname), temp(i)), the _textbox(i) part returns Nothing so the attempted reference to the DataBindings property fails, because it doesn’t exist.