List of txtBoxes - System.NullReferenceException:

Question

Edit: this is not a duplicate of "what is System.NullReferenceException", I'm aware of what the exception is just not what was causing it in this specific case. However someone already answered in the comments. Thanks!

So I have a program where I need to loop through some Text-boxes, at first I used this,

For Each tb As TextBox In Me.Controls.OfType(Of TextBox)() 
    tb.Enabled = True
    tb.Clear()
Next

Which works like a charm. Problem is that this loops through every single textbox, and now I added new boxex that don't need to end up in this loop. I tried using a list and an array to replace this, but I keep getting the "System.NullReferenceException" exception.

Dim boxList As New List(Of TextBox)(
{
    txtCourse1,
    txtCourse2,
    txtCourse3,
    txtCourse4,
    txtCourse5,
    txtCourse6
})

Here is my list declaration, and here is how I use it,

For Each tb As TextBox In boxList 
    tb.Enabled = True
    tb.Clear()
Next

The values in the text-boxes never seem to enter the loop, hence the exception. Same thing happens with an array, what am I doing wrong? Thanks in advance.

Where are the `boxList` initialization and the For-Each-loop? — Olivier Jacot-Descombes, Feb 17 '19 at 21:08
the foreach loop is inside a sub function, the list is inside the class, outside of the function. — Brian Naranjo, Feb 17 '19 at 21:09
If you add the textbox to the list before they are initialized you have the null ref exception because at that point in time your textboxes are still null. Move the initialization of the list inside the Form_Load event — Steve, Feb 17 '19 at 21:10
The problem is that if it is inside the class, it is executed **before** the textboxes are created. Therefore the list will be filled with Nothings. Keep `Dim boxList As List(Of TextBox)` where it is but put `boxList = New List(Of TextBox)( { ... }` in the load event handler. — Olivier Jacot-Descombes, Feb 17 '19 at 21:10

List of txtBoxes - System.NullReferenceException:

0 Answers0