FOR statement conflicting with IF statement in VB - vb.net

Question

I am creating a fairly simple ping tool which shows in milliseconds how long the server took to respond. If the server does not respond, it shows as it responded in 0ms. I wanted to implement an If statement to write Server failed to respond in the ListBox rather than it replied in 0ms. The only problem with this is I have a chunk of code which need to be run outside the If but continues inside the If and involves using the line of code Next... This seems to cause the If statement to not recognise the End If and the End If to not recognise the If...
Here is my code:
For i As Integer = 0 To numberOfPings - 1
Dim ping As New Ping
Dim pingRe As PingReply = ping.Send(pingTarget)
If pingRe.RoundtripTime = 0 Then
Me.listboxPing.Items.Add("Server failed to respond...")
Else
Me.listboxPing.Items.Add("Response from " & pingTarget & " in " & pingRe.RoundtripTime.ToString() & "ms")
listboxPing.SelectedIndex = listboxPing.Items.Count - 1
listboxPing.SelectedIndex = -1
Application.DoEvents()
Threading.Thread.Sleep(500)
Next
Me.listboxPing.Items.Add("")
End If
Does anyone know of a way I could fix this/get around this issue?
Thanks,

Answer 1

If I were going to write code to ping an address and show the results it would look something like this.
Dim pingThrd As Threading.Thread
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
If pingThrd Is Nothing OrElse pingThrd.ThreadState = Threading.ThreadState.Stopped Then
RichTextBox1.Clear()
pingThrd = New Threading.Thread(AddressOf PingIt)
pingThrd.IsBackground = True
pingThrd.Start("192.168.33.1")
End If
End Sub
Public Sub PingIt(pingTarget As Object)
Dim numberOfPings As Integer = 5
Dim pingT As String = DirectCast(pingTarget, String)
Dim pingTimeOut As Integer = 1000
Const dlyBetweenPing As Integer = 500
Dim dspStr As String
For i As Integer = 0 To numberOfPings - 1
Dim pingit As New Ping
Dim pingRe As PingReply = pingit.Send(pingT, pingTimeOut)
'check if success
If pingRe.Status = IPStatus.Success Then
dspStr = String.Format("Response from: {0} in {1}ms.", pingRe.Address, pingRe.RoundtripTime)
Else
dspStr = String.Format("{0} failed. Status: {1}", pingRe.Address, pingRe.Status)
End If
Me.BeginInvoke(Sub()
RichTextBox1.AppendText(dspStr)
RichTextBox1.AppendText(Environment.NewLine)
End Sub)
Threading.Thread.Sleep(dlyBetweenPing)
Next
End Sub
edit: Same basic code but allow thread to start with different address and count.
Structure PingWhat
Dim addr As String
Dim howmany As Integer
End Structure
Dim pingThrd As Threading.Thread
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
If pingThrd Is Nothing OrElse pingThrd.ThreadState = Threading.ThreadState.Stopped Then
RichTextBox1.Clear()
'setup a thread to do the actual ping'ing
'this allows the UI to function
pingThrd = New Threading.Thread(AddressOf PingIt)
pingThrd.IsBackground = True
'setup address to ping and howmany times to ping it
Dim somePing As New PingWhat With {.addr = "192.168.33.1", .howmany = 3}
'start the thread
pingThrd.Start(somePing)
End If
End Sub
Public Sub PingIt(pingTarget As Object)
Dim pingT As PingWhat = DirectCast(pingTarget, PingWhat)
Dim pingTimeOut As Integer = 1000
Const dlyBetweenPing As Integer = 500
Dim dspStr As String
For i As Integer = 1 To pingT.howmany
Dim pingit As New Ping
Dim pingRe As PingReply = pingit.Send(pingT.addr, pingTimeOut)
'check if success
If pingRe.Status = IPStatus.Success Then
dspStr = String.Format("Response from: {0} in {1} ms.", pingRe.Address, pingRe.RoundtripTime)
Else
dspStr = String.Format("Ping Failed {0}. Status: {1}", pingT.addr, pingRe.Status)
End If
'update the UI
Me.BeginInvoke(Sub()
RichTextBox1.AppendText(dspStr)
RichTextBox1.AppendText(Environment.NewLine)
RichTextBox1.ScrollToCaret()
End Sub)
Threading.Thread.Sleep(dlyBetweenPing)
Next
Me.BeginInvoke(Sub()
RichTextBox1.AppendText("Done")
RichTextBox1.AppendText(Environment.NewLine)
RichTextBox1.ScrollToCaret()
End Sub)
End Sub

Answer 2

Is this what you're after?
For i As Integer = 0 To numberOfPings - 1
Dim ping As New Ping
Dim pingRe As PingReply = ping.Send(pingTarget)
If pingRe.RoundtripTime = 0 Then
Me.listboxPing.Items.Add("Server failed to respond...")
Else
Me.listboxPing.Items.Add("Response from " & pingTarget & " in " & pingRe.RoundtripTime.ToString() & "ms")
listboxPing.SelectedIndex = listboxPing.Items.Count - 1
listboxPing.SelectedIndex = -1
Application.DoEvents()
Threading.Thread.Sleep(500)
add = True
Exit For
End If
Next
If add Then Me.listboxPing.Items.Add("")
The If will change the scope, therefore, you need to use a variable to check whether it went into the Else part.
Of course, you need to close the first If before the Next.

Answer 3

#dbasnett This was the code I using before and it was absolutely perfect for what i needed EXCEPT if a ping failed it would just say (PingTarget) responded in 0ms which is not ideal. Ideally i would like it to say Server failed to respond... . Do you know a way in which this can be achieved by modifying my original code?
Imports System.Net.NetworkInformation
Imports System.Runtime.InteropServices
Public Class PingClient
Private Const EM_SETCUEBANNER As Integer = &H1501
<DllImport("user32.dll", CharSet:=CharSet.Auto)>
Private Shared Function SendMessage(ByVal hWnd As IntPtr, ByVal msg As Integer, ByVal wParam As Integer, <MarshalAs(UnmanagedType.LPWStr)> ByVal lParam As String) As Int32
End Function
Private Sub SetCueText(ByVal control As Control, ByVal text As String)
SendMessage(control.Handle, EM_SETCUEBANNER, 0, text)
End Sub
Private Sub PingClient_Load(sender As Object, e As EventArgs) Handles MyBase.Load
SetCueText(textboxIP, "IP Address/Domain")
SetCueText(textboxPing, "No. Of Pings")
End Sub
Structure PingWhat
Dim addr As String
Dim howmany As Integer
End Structure
Dim pingThrd As Threading.Thread
Public Sub buttonPing_Click(sender As Object, e As EventArgs) Handles buttonPing.Click
If pingThrd Is Nothing OrElse pingThrd.ThreadState = Threading.ThreadState.Stopped Then
Dim pingTarget As String = ""
Dim numberOfPings As Integer = 0
Dim intTimeout As Integer = 2000
If String.IsNullOrEmpty(textboxIP.Text) Then
MsgBox("You must enter an IP Address or Domain.")
Exit Sub
End If
If Not Int32.TryParse(textboxPing.Text, numberOfPings) Then
MsgBox("You must enter a number of how many times the target address will be pinged.")
Exit Sub
End If
If numberOfPings = 0 Then
MsgBox("You must enter a value over 0.")
textboxPing.Clear()
Exit Sub
End If
'setup a thread to do the actual ping'ing
'this allows the UI to function
pingThrd = New Threading.Thread(AddressOf PingIt)
pingThrd.IsBackground = True
'setup address to ping and howmany times to ping it
Dim somePing As New PingWhat With {.addr = pingTarget, .howmany = numberOfPings}
'start the thread
pingThrd.Start(somePing)
End If
Me.listboxPing.Items.Add("")
End Sub
Public Sub PingIt(pingTarget As Object)
Dim pingT As PingWhat = DirectCast(pingTarget, PingWhat)
Dim pingTimeOut As Integer = 1000
Const dlyBetweenPing As Integer = 500
Dim dspStr As String
For i As Integer = 1 To pingT.howmany
Dim pingit As New Ping
Dim pingRe As PingReply = pingit.Send(pingT.addr, pingTimeOut)
'check if success
If pingRe.Status = IPStatus.Success Then
dspStr = String.Format("Response from: {0} in {1} ms.", pingRe.Address, pingRe.RoundtripTime)
Else
dspStr = String.Format("Ping Failed {0}. Status: {1}", pingT.addr, pingRe.Status)
End If
'update the UI
Me.BeginInvoke(Sub()
listboxPing.Items.Add(dspStr)
End Sub)
Threading.Thread.Sleep(dlyBetweenPing)
Next
Me.BeginInvoke(Sub()
listboxPing.Items.Add("Done")
End Sub)
End Sub
Private Sub PingClient_Closing(sender As Object, e As System.ComponentModel.CancelEventArgs) Handles MyBase.Closing
Dim Response As Integer
Response = MsgBox("Are you sure you want to exit the Ping Tool?", 36)
If Response = MsgBoxResult.Yes Then
Else
e.Cancel = True
End If
End Sub
End Class