Solved

vb.net and background worker for system uptime

Posted on 2014-12-08
11
322 Views
Last Modified: 2014-12-09
I am attempting to write a small amount of code to return to me the system uptime of a remote workstation.  It works when ran directly from a button, but when i try to put it in a background thread it fails everytime.

Below is the code i am using:

Private Sub BackgroundWorker1_DoWork(sender As Object, e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
        Dim worker As BackgroundWorker = CType(sender, BackgroundWorker)
        Try
            Dim str_ServerName As String = TextBox1.Text
            Dim pc As New PerformanceCounter("System", "System Up Time", "", str_ServerName)
            pc.NextValue()
            Dim ts As TimeSpan = TimeSpan.FromSeconds(pc.NextValue)
            MsgBox(str_ServerName & " has been up for " & ts.Days & " days, " & ts.Hours & " hours, " & ts.Minutes & " minutes, " & " and " & ts.Seconds & " seconds.", , "System Uptime")
        Catch ex As Exception
            MsgBox("Workstation Uptime not found", MsgBoxStyle.Information, "Information")
        End Try
    End Sub

    Private Sub BackgroundWorker1_ProgressChanged(sender As Object, e As System.ComponentModel.ProgressChangedEventArgs) Handles BackgroundWorker1.ProgressChanged

    End Sub

    Private Sub BackgroundWorker1_RunWorkerCompleted(sender As Object, e As System.ComponentModel.RunWorkerCompletedEventArgs) Handles BackgroundWorker1.RunWorkerCompleted
        If e.Cancelled = True Then
        End If
    End Sub

Open in new window


I declare the below:
Private bw As BackgroundWorker = New BackgroundWorker
    Public Sub New()
        InitializeComponent()
        bw.WorkerReportsProgress = True
        bw.WorkerSupportsCancellation = True
        AddHandler bw.DoWork, AddressOf BackgroundWorker1_DoWork
        AddHandler bw.ProgressChanged, AddressOf BackgroundWorker1_ProgressChanged
        AddHandler bw.RunWorkerCompleted, AddressOf BackgroundWorker1_RunWorkerCompleted
    End Sub

Open in new window


I then try to run the method from a button:
  If Not bw.IsBusy = True Then
            bw.RunWorkerAsync()
        End If

Open in new window


What am i doing wrong?
0
Comment
Question by:derek7467
11 Comments
 
LVL 44

Expert Comment

by:AndyAinscow
ID: 40487474
The background worker doesn't support UI - eg. MessageBox - elements.  You would need to pass the uptime back to the main thread to display the result.
0
 

Author Comment

by:derek7467
ID: 40487476
This is the error i get:

Cross-thread operation not valid: Control 'TextBox1' accessed from a thread other than the thread it was created on.
0
 

Author Comment

by:derek7467
ID: 40487478
How do i pass it back?
0
Technology Partners: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

 

Author Comment

by:derek7467
ID: 40487492
I supposed this would be bad coding to use the below???

TextBox.CheckForIllegalCrossThreadCalls = false
0
 
LVL 40

Expert Comment

by:Kyle Abrahams
ID: 40487519
Use a BeginInvoke to bubble it up to the UI thread:
http://msdn.microsoft.com/en-us/library/a06c0dc2(v=vs.110).aspx?cs-save-lang=1&cs-lang=vb#code-snippet-1
Me.BeginInvoke(new Delegate(AddressOf showMsgBox),  str_ServerName & " has been up for " & ts.Days & " days, " & ts.Hours & " hours, " & ts.Minutes & " minutes, " & " and " & ts.Seconds & " seconds.", "System Uptime")

public sub showMessageBox(text as string, Caption as string)
 MsgBox(text, , Caption)
end sub

Open in new window

0
 
LVL 1

Expert Comment

by:Michael O'Shea
ID: 40487522
Hi, I suggest all will become clear when you Google "InvokeRequired"
0
 
LVL 86

Accepted Solution

by:
Mike Tomlinson earned 500 total points
ID: 40487875
First, pass the Computer Name to RunWorkerAsync():
    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        If Not bw.IsBusy = True Then
            bw.RunWorkerAsync(TextBox1.Text)
        End If
    End Sub

Open in new window


Then you can grab it in DoWork() with "e.Argument".  Set "e.Result" to your output:
    Private Sub BackgroundWorker1_DoWork(sender As Object, e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
        Dim worker As BackgroundWorker = CType(sender, BackgroundWorker)
        Try
            Dim str_ServerName As String = e.Argument.ToString
            Dim pc As New PerformanceCounter("System", "System Up Time", "", str_ServerName)
            pc.NextValue()
            Dim ts As TimeSpan = TimeSpan.FromSeconds(pc.NextValue)
            e.Result = str_ServerName & " has been up for " & ts.Days & " days, " & ts.Hours & " hours, " & ts.Minutes & " minutes, " & " and " & ts.Seconds & " seconds."
        Catch ex As Exception
            e.Result = "Workstation Uptime not found"
        End Try
    End Sub

Open in new window


Finally, grab "e.Result" in the RunWorkerCompleted() event:
    Private Sub BackgroundWorker1_RunWorkerCompleted(sender As Object, e As RunWorkerCompletedEventArgs) Handles BackgroundWorker1.RunWorkerCompleted
        Dim result As String = e.Result
        MessageBox.Show(result)
    End Sub

Open in new window

0
 
LVL 75

Expert Comment

by:käµfm³d 👽
ID: 40488071
I agree with Mike:  The BW supports passing data back to the UI via its established events. There is no need for CheckForIllegalCrossThreadCalls, BeginInvoke, or InvokeRequired as the others have mentioned.
0
 
LVL 44

Expert Comment

by:AndyAinscow
ID: 40488223
From the help files about the BackgroundWorker:
http://msdn.microsoft.com/en-us/library/cc221403%28v=vs.95%29.aspx

To pass data back to the calling process, set the Result property of the DoWorkEventArgs object that is passed to the event handler. This value can be read when the RunWorkerCompleted event is raised at the end of the operation.
0
 

Author Closing Comment

by:derek7467
ID: 40488792
thank you
0
 
LVL 44

Expert Comment

by:AndyAinscow
ID: 40488875
ps.
Reading the help files could result in a quicker answer than just asking a question and waiting.
0

Featured Post

Free Tool: IP Lookup

Get more info about an IP address or domain name, such as organization, abuse contacts and geolocation.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

It’s quite interesting for me as I worked with Excel using vb.net for some time. Here are some topics which I know want to share with others whom this might help. First of all if you are working with Excel then you need to Download the Following …
More often than not, we developers are confronted with a need: a need to make some kind of magic happen via code. Whether it is for a client, for the boss, or for our own personal projects, the need must be satisfied. Most of the time, the Framework…
Are you ready to implement Active Directory best practices without reading 300+ pages? You're in luck. In this webinar hosted by Skyport Systems, you gain insight into Microsoft's latest comprehensive guide, with tips on the best and easiest way…

726 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question