null reference exeption - Xtreme Visual Basic Talk

07-13-2012, 11:06 PM

Amerigo

Centurion

Join Date: Jan 2009

Location: USA

Posts: 127

null reference exeption

I get this unexplainable error when running this. Using a msgbox right before the error, everything has a value.

Code:

Public Class Form1
    Private ReadOnly RNG As New Random()
    Dim MyList As New List(Of String)
    Dim di As New IO.DirectoryInfo(Application.StartupPath & "\Images")
    Dim diar1 As IO.FileInfo() = di.GetFiles()
    Dim dra As IO.FileInfo
    Dim card() As String

    Private Sub Deal_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Deal.Click
        Shuffle()
    End Sub

    Private Sub Shuffle()

        For Each dra In diar1
            MyList.Add(dra.FullName)
        Next

        While MyList.Count > 0
            For i As Integer = 1 To 4
                Dim index = RNG.Next(0, MyList.Count)
                card(i) = MyList(index) <<< ERROR HERE

                Select Case i
                    Case 1
                        Card1.Image = Image.FromFile(card(i))
                    Case 2
                        Card2.Image = Image.FromFile(card(i))
                    Case 3
                        Card3.Image = Image.FromFile(card(i))
                    Case 4
                        Card4.Image = Image.FromFile(card(i))
                    Case 5
                        Card5.Image = Image.FromFile(card(i))
                End Select
                MyList.RemoveAt(index)
            Next
        End While
    End Sub

End Class

__________________
Amerigo

07-14-2012, 07:54 AM

AtmaWeapon

Fabulous Florist

Forum Leader
* Guru *

Join Date: Feb 2004

Location: Austin, TX

Posts: 9,416

Are you /sure/ everything has a value? Your code never initializes card().

__________________
.NET Resources
My FAQ threads | Tutor's Corner | Code Library
I would bet money 2/3 of .NET questions are already answered in one of these three places.

07-14-2012, 08:07 AM

Amerigo

Centurion

Join Date: Jan 2009

Location: USA

Posts: 127

msgbox(card(i)) placed before the error pops up the randomly chosen file path as intended. What would I need to do to "initialize" Card()?

Never mind. I eliminated the (i) since I'm using 'Select Case i', I don't need it. Working now.

__________________
Amerigo

07-14-2012, 09:50 AM

AtmaWeapon

Fabulous Florist

Forum Leader
* Guru *

Join Date: Feb 2004

Location: Austin, TX

Posts: 9,416

Code:

Dim card() As String

This line says "I want a variable named 'card' that can hold an array of Strings, but I don't want the array yet; I'll create it later." For an array to be initialized, you have to provide a size. Since you haven't, there's no sensible array to create so card holds Nothing.

You can initialize an array by giving it a size at creation:

Code:

Dim card(5) As String ' 6 elements

You can also set value with an initializer; VB will auto-calculate the size:

Code:

Dim card() As String = { "", "", "", "", "" }

After declaration, you have to use the ReDim statement to initialize the array:

Code:

ReDim(card, 5) ' 6 elements

That says "Create a 6-element array and assign it to the variable card."

If you don't do any of these steps, the variable is Nothing because it has not been assigned a value.

If that message box is working as you describe, there is code you aren't showing, and I can't tell you about what I can't see.

__________________
.NET Resources
My FAQ threads | Tutor's Corner | Code Library
I would bet money 2/3 of .NET questions are already answered in one of these three places.