Question

i wonder what is wrong with the following vb.net code.

Public Class Form10

Public IDs() As String = TextBox1.Text.Split(",")

Private Sub Form10_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
End Sub

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    For Each id In IDs
        MsgBox(id)
    Next
End Sub

End Class

when i do

Form10.show()

i get an error “Object reference not set to an instance”

Answer 1

You have declared a field in your class to be initialized with a value from a control on the corresponding form that does not yet exist. The control is not initialized and loaded by the time your initializer on your field member is accessed, thus causing the error.

To keep the public IDs declaration, you could remove the initialization from the field declaration, then move the assignment to the Button1_Click event, as follows:

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    IDs=TextBox1.Text.Split(",")
    ' Do something interesting with IDs now...
End Sub