Re: Check Internet connection on background thread and update UI

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From: Daniel Moth (dmoth74_at_hotmail.com)
Date: 02/23/05 

Date: Wed, 23 Feb 2005 22:21:48 -0000

Some suggestions

0. If a method does not return anything, make it a Sub not a Function
1. Turn Option Strict On
2. Do not start a threading timer at creation rather pass -1 as the timeout.
When you start it, do so with the Change method.
3. Never use the interval. I.e. the second parameter of the constructor and
the Change method is always -1; this avoids reentrancy.
4. Following from point 3, when the timer calls you back and only at the
very end of the method, call Change again thus running the timer again (if
you need to run it).
5. If the webresponse.statuscode is OK, there should be no point checking
the contentlength; you can connect.

Cheers
Daniel 

--
http://www.danielmoth.com/Blog/
"salimgbelim" <salimgbelim@gmail.com> wrote in message
news:1109156468.179379.245400@l41g2000cwc.googlegroups.com...
> Hi Guys,
>
> It seems to be a very simple thing,but unfortunately I can't succeed so
> i thought to post a question to get new Ideas.
>
> My problem is : I want a thread running in background to check wether
> Internet Conection is available,if so update the property on the form
> to True or else False(ideally i want a image to be updated on form
> (online/offline image))
>
> Below is my Code which nearly works but the application hangs
> eventually after some time on device it works fine on emulator :-(
>
> Any inputs or new/better way or doing this???
>
> Regards
> Salim
>
> CODE :
> -------------------------------------------------------------------------------------
> Imports System
> Imports System.Threading
> Imports eXml.ExpenseWorld.SmartDevice.PocketPC
> Imports System.Net
>
> Public Class TimerTesting
>    Inherits System.Windows.Forms.Form
>
> #Region " Windows Form Designer generated code "
>
>    Public Sub New()
>        MyBase.New()
>
>        'This call is required by the Windows Form Designer.
>        InitializeComponent()
>
>        'Add any initialization after the InitializeComponent() call
>        ' Create the delegate that invokes methods for the timer.
>        Dim timerDelegate As New TimerCallback(AddressOf CheckStatus)
>
>        ' Create a timer that waits one second, then invokes every
> second.
>        Dim Timer = New Timer(timerDelegate, s, 1000, 1000)
>        s.tmr = Timer
>
>    End Sub
>
>    Protected Overloads Overrides Sub Dispose(ByVal disposing As
> Boolean)
>        MyBase.Dispose(disposing)
>    End Sub
>
>    Private s As New TimerExampleState
>
>    'NOTE: The following procedure is required by the Windows Form
> Designer
>    'It can be modified using the Windows Form Designer.
>    'Do not modify it using the code editor.
>    Friend WithEvents Button1 As System.Windows.Forms.Button
>    <System.Diagnostics.DebuggerStepThrough()> Private Sub
> InitializeComponent()
>        Me.Button1 = New System.Windows.Forms.Button
>        '
>        'Button1
>        '
>        Me.Button1.Location = New System.Drawing.Point(88, 56)
>        Me.Button1.Text = "Button1"
>        '
>        'TimerTesting
>        '
>        Me.ClientSize = New System.Drawing.Size(282, 270)
>        Me.Controls.Add(Me.Button1)
>        Me.Text = "TimerTesting"
>
>    End Sub
>
> #End Region
>
> #Region "Properties"
>
>    Private mIsconnected As Boolean
>    Private Property Isconnected() As Boolean
>        Get
>            Return Me.mIsconnected
>        End Get
>        Set(ByVal Value As Boolean)
>            Me.mIsconnected = Value
>        End Set
>    End Property
>
> #End Region
>
> #Region " Private sub"
>
>    Public Sub CheckStatus(ByVal state As [Object])
>        Dim st As TimerExampleState = CType(state, TimerExampleState)
>        st.counter += 1
>        Me.CheckConnection()
>        Me.Invoke(New EventHandler(AddressOf UpdateInterface))
>    End Sub
>
>    Private Sub UpdateInterface(ByVal sender As Object, ByVal e As
> System.EventArgs)
>        'If Me.mIsconnected = False Then
>        '    Me.mOnlineStatus.Online = False
>        '    Me.mOnlineStatus.Update()
>        '    MessageBox.Show(mLength.ToString)
>        'Else
>        '    Me.mOnlineStatus.Online = True
>        '    Me.mOnlineStatus.Update()
>        'End If
>    End Sub
>
>    Private Function CheckConnection() As Boolean
>        If Me.IsCConnected() = True Then
>            Me.mIsconnected = True
>        Else
>            Me.mIsconnected = False
>        End If
>    End Function
>
>    Public Function IsCConnected() As Boolean
>
>        Dim hwrRequest As HttpWebRequest
>        Dim hwrResponse As HttpWebResponse
>
>        Dim strUrl As String = "http://www.google.com/"
>        Dim bConnected As Boolean = False
>
>        Try
>            hwrRequest = CType(WebRequest.Create(strUrl),
> HttpWebRequest)
>            hwrResponse = CType(hwrRequest.GetResponse(),
> HttpWebResponse)
>            hwrRequest.Abort()
>
>            If hwrResponse.StatusCode = HttpStatusCode.OK Then
>                If hwrResponse.ContentLength <= 0 Then
>                    bConnected = False
>                Else
>                    bConnected = True
>                End If
>            End If
>            hwrResponse.GetResponseStream.Close()
>        Catch we As WebException
>            bConnected = False
>        Catch ex As Exception
>            bConnected = False
>        Finally
>            hwrRequest = Nothing
>            hwrResponse = Nothing
>        End Try
>
>        Return bConnected
>
>    End Function
>
> #End Region
>
> #Region "Event Handler - Button"
>
>    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As
> System.EventArgs) Handles Button1.Click
>        If Me.mIsconnected = True Then
>            MessageBox.Show("Online")
>        Else
>            MessageBox.Show("Offline")
>        End If
>    End Sub
>
> #End Region
>
> #Region "Private Class"
>
>    Class TimerExampleState
>        Public counter As Integer = 0
>        Public tmr As Timer
>    End Class
>
> #End Region
>
> End Class
>
> END CODE :
> -------------------------------------------------------------------------------------
>
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