Do functions return values as byref or byval or?

[algea]

Hi again
i have a strange issue today. Sample code is at the below of the post. The code that i have pointed out is too strange. According to my knowledge using return statement the functions return values as byval and copies the value to the stack. Also how can my class can reach outscope elements and change them. Take a look at to the code below. How this could be?

Public Class Form1
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim b As New ByteClass
        Dim sumArray As Long = 0
        Dim ByteArray As Byte() = {}
        Dim idx As Integer = 0
        ByteArray = b.GetArray
        sumArray = SumByteArray(ByteArray)
        Do
            idx += 1
            If sumArray <> SumByteArray(ByteArray) Then Exit Do
            Debug.Print("Not changed yet" + "" + Str(idx))
        Loop
        MsgBox("The ByteArray has changed???")
    End Sub
 
    Public Function SumByteArray(ByVal pByteArray As Byte()) As Long
        'This function return the sum value of the ByteArray
        Dim retval As Long = 0
        For i As Integer = 0 To pByteArray.Length - 1
            retval = retval + pByteArray(i)
        Next
        Return retval
    End Function
End Class
Class ByteClass
    Dim ByteArray As Byte() = {}
    Dim Foo As System.Threading.Thread
    Sub New()
        ByteArray = New Byte(4096) {}
        Foo = New System.Threading.Thread(AddressOf ThreadWork)
        Foo.Start()
    End Sub
    Public Function GetArray() As Byte()
        Return ByteArray
    End Function
    Sub ThreadWork()
        'Generate a random mutation on bytestream
        Dim r1 As New Random
        Dim r2 As New Random
        Dim idx As Integer
        Dim v As Integer = 0
        Do
            v = r1.Next(0, 255 + 1)
            idx = r2.Next(0, 4096 + 1)
            ByteArray(idx) = v
            Application.DoEvents()
        Loop
    End Sub
End Class