Multi-Threading IP Address Pings Causing Application Crash - vb.net

Question

Boy, learning something new can be a real headache if you can't find a solid source. I have been designing applications in a linear fashion for some time now and want to step up into a more powerful approach. I have been reading up on threading, and perhaps have gone to an larger level than I should. However, one usually steps up when the application calls for it and no better time than the present to learn something new.
My program is designed to do something that seems rather simple, but has become extremely difficult to create in a smooth running manor. The original design created object of each device on the network it wished to ping, in my real world environment they are Kindles. The goal was to ensure they were still connected to the network by Pining them. I used a For Loop and Obj Array to do this set on a Timer. This had unexpected results causing the ListView to flicker and load slowly after the ListView1.Items.Clear. I evolved into updating the List Items rather than clearing them and the flicker remained.
I assumed this was due to the slow process of the array and pings so I started hunting for solutions and came across Multi-Threading. I have known about this for some time, but have yet to dive into the practice. My program seemed to need more speed and smoother operation so I took a stab at it. The below code in its complete form is the result, however it crashes and throws errors. Clearly I have not used Threading as it was intended. Using it in simpler functions works fine and I feel I have the grasp. That is if i want my program to pointlessly run counters.
I don't know what to do next in my steps for getting this task done, and figure I am combining several different methods into a mush of dead program. I could really use some help getting back on track with this. All comments welcome and thank you for checking out my code.
Form1 Code
Public Class Form1
'Obj Array
Public Shared objDevice As New List(Of kDevice)
'Thread Array for each Obj
Public Shared thread() As System.Threading.Thread
Private Sub ipRefresh(objID, itemPos)
Dim objDev As kDevice = objID
If My.Computer.Network.Ping(objDev.kIP) Then
objDev.kStatus = "Online"
objDev.kPings = 0
Else
objDev.kPings += 1
End If
If objDev.kPings >= 8 Then
objDev.kStatus = "Offline"
objDev.kPings = 0
ListView1.Items(itemPos).BackColor = Color.Red
End If
Dim str(4) As String
Dim itm As ListViewItem
str(0) = objDev.kName
str(1) = objDev.kIP
str(2) = objDev.kStatus
str(3) = objDev.kPings
itm = New ListViewItem(str)
ListView1.Items(itemPos) = itm
End Sub
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Me.CheckForIllegalCrossThreadCalls = False
' Adding ListView Columns
ListView1.Columns.Add("Device", 100, HorizontalAlignment.Left)
ListView1.Columns.Add("IP Address", 150, HorizontalAlignment.Left)
ListView1.Columns.Add("Status", 60, HorizontalAlignment.Left)
ListView1.Columns.Add("Pings", 60, HorizontalAlignment.Left)
Dim ipList As New List(Of String)
Dim nameList As New List(Of String)
Using MyReader As New Microsoft.VisualBasic.FileIO.TextFieldParser("kDevices.csv")
MyReader.TextFieldType = Microsoft.VisualBasic.FileIO.FieldType.Delimited
MyReader.Delimiters = New String() {","}
Dim currentRow As String()
Dim rowP As Integer = 1
While Not MyReader.EndOfData
Try
currentRow = MyReader.ReadFields()
Dim cellP As Integer = 0
Dim nTemp As String = ""
For Each currentField As String In currentRow
Select Case cellP
Case 0
nameList.Add(currentField.Replace("""", ""))
Case 1
ipList.Add(currentField.Replace("""", ""))
End Select
cellP += 1
Next
Catch ex As Microsoft.VisualBasic.FileIO.MalformedLineException
MsgBox("Line " & ex.Message & " is invalid. Skipping")
End Try
rowP += 1
End While
End Using
Dim nameLAR As String() = nameList.ToArray
Dim ipLAR As String() = ipList.ToArray
ReDim Preserve thread(nameLAR.Length)
For i As Integer = 0 To nameLAR.Length - 1
Dim newDevice As New kDevice
Dim objNum = i
objDevice.Add(newDevice)
newDevice.kName = nameLAR(i)
newDevice.kIP = ipLAR(i)
If My.Computer.Network.Ping(newDevice.kIP) Then
newDevice.kStatus = "Online"
Else
newDevice.kStatus = "Loading"
End If
Dim str(4) As String
Dim itm As ListViewItem
str(0) = newDevice.kName
str(1) = newDevice.kIP
str(2) = newDevice.kStatus
str(3) = newDevice.kPings
itm = New ListViewItem(str)
If newDevice.kStatus = "Loading" Then
itm.BackColor = Color.Yellow
End If
ListView1.Items.Add(itm)
thread(objNum) = New System.Threading.Thread(Sub() Me.ipRefresh(objDevice(objNum), objNum))
Next
End Sub
Private Sub Timer1_Tick(sender As Object, e As EventArgs) Handles Timer1.Tick
For i As Integer = 0 To objDevice.Count - 1
thread(i).Start()
Next
End Sub
End Class
kDevice Class
Public Class kDevice
Private strkName As String
Private strkIP As String
Private strkStatus As String
Private strkLastStatus As String
Private strkPings As Integer = 0
Public Property kName As String
Get
Return strkName
End Get
Set(value As String)
strkName = value
End Set
End Property
Public Property kIP As String
Get
Return strkIP
End Get
Set(value As String)
strkIP = value
End Set
End Property
Public Property kStatus As String
Get
Return strkStatus
End Get
Set(value As String)
strkStatus = value
End Set
End Property
Public Property kPings As Integer
Get
Return strkPings
End Get
Set(value As Integer)
strkPings = value
End Set
End Property
End Class
The Error / Crash on Line 32 of my code which is when it tries to pass the update to the ListView Item
An unhandled exception of type 'System.ArgumentException'
occurred in Microsoft.VisualBasic.dll
Additional information: InvalidArgument=Value of '18'
is not valid for 'index'.
or
An unhandled exception of type 'System.NullReferenceException'
occurred in Microsoft.VisualBasic.dll
Additional information: Object reference not set to an instance
of an object.
If my code does not make sense, or at lease the idea of what I was trying to make it do, please let me know and I will explain whichever parts are unclear. Again thank you for looking over my issue.

Answer 1

Just a possible issue I noticed:
Dim str(4) As String
Dim itm As ListViewItem
str(0) = newDevice.kName
str(1) = newDevice.kIP
str(2) = newDevice.kStatus
str(3) = newDevice.kPings
itm = New ListViewItem(str)
If newDevice.kStatus = "Loading" Then
itm.BackColor = Color.Yellow
End If
ListView1.Items.Add(itm)
In this bit here, you declare str(4) which would be 5 possible indexes (remember it starts at zero), where you should have 4 (str(3)) . I don't think this is the whole issue, but just a small bit you should probably fix. You also may want to look into other ways to update the listview without setting
Me.CheckForIllegalCrossThreadCalls = False
Here's an awesome guide that helped me when I did my first multi threaded application: http://checktechno.blogspot.com/2012/11/multi-thread-for-newbies.html