Error in Visual Basic loop

Question

Apparently i got it wrong in the second if condition of the loop, i leave a picture for better understanding.

For some reason the error is not displayed in the first if condition even tho they are pretty much the same.

To put this in context i have a big first textbox and other 9 small ones. Basically i want to send the value i write in the big textbox to the small ones one by one.

Big TextBox name attribute is t0 while the others go from t1 to t9

VISUAL BASIC CODE

 Public Class Form1

        Dim array() As TextBox = {t1, t2, t3, t4, t5, t6, t7, t8, t9}

        Private Sub t0_KeyDown(sender As Object, e As System.Windows.Forms.KeyEventArgs) Handles t0.KeyDown
            If e.KeyCode = Keys.Enter Then

                If sender.Text.ToString <> String.Empty Then

                    For indice As Integer = 0 To array.Length - 1

                        If array(indice).Text = String.Empty Then '<== The error is in this line

                            array(indice).Text = sender.Text.ToString

                            Exit For

                        End If

                    Next

                End If

            End If

        End Sub

    End Class

UPDATE

Used equals this time but still the same error

so, your array doesn't seem to have this index or the value is null ;) — Icepickle
– Icepickle, Commented Feb 6, 2018 at 10:27
You are right, what is the correct way of declaring an array of textboxs, there is obviusly something wrong with mine. Note that i changed my textbox elements name to t0 up to t9 — Rddevelop
– Rddevelop, Commented Feb 6, 2018 at 10:34

Sebastian Brosch · Accepted Answer · 2018-02-06 10:51:16Z

1

An item of your array seems to be Nothing. You can avoid such an error by using the following if condition (using AndAlso):

If TypeOf(array(indice)) Is TextBox AndAlso array(indice).Text = String.Empty Then
    array(indice).Text = sender.Text.ToString
    Exit For
End If

Note: Your first if condition doesn't use the array so the error doesn't happen there.

But the problem isn't the if condition! You defined the array to early. At the time you defined the array the controls of the form are not initialized (so every control is Nothing until InitializeComponent in method / constructor New is called).

You can initialize the array directly on the KeyDown event to make sure the TextBox elements are created / initialized.

Private Sub t0_KeyDown(sender As Object, e As System.Windows.Forms.KeyEventArgs) Handles t0.KeyDown
    If e.KeyCode = Keys.Enter Then
        If sender.Text.ToString <> String.Empty Then
            Dim array() As TextBox = {t1, t2, t3, t4, t5, t6, t7, t8, t9}

            For indice As Integer = 0 To array.Length - 1
                If TypeOf(array(indice)) Is TextBox AndAlso array(indice).Text = String.Empty Then
                    array(indice).Text = sender.Text.ToString
                    Exit For
                End If
            Next
        End If
    End If
End Sub

Another solution to use the array globally too, is to initialize the array on the form Load event.

edited Feb 6, 2018 at 10:51

answered Feb 6, 2018 at 10:30

Sebastian Brosch

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3 Comments

Rddevelop Over a year ago

You are right, my array indexes seem to be null, what is the correct way of declaring an array of textbox? Note that i changed my textboxs name attributes to t0 up to t9

Rddevelop Over a year ago

Thanks a lot, your solution works as expected, i put the declaration in the load method and works well too, is there any explanation why it doesnt work declaring the array out of the form methods.

Rddevelop Over a year ago

Saw the update, i understand now, as in android there are methods that are called automatically and will load the interface and components, so you can not reference those components before they are loaded. Thanks!

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