BackgroundWorker doesn't trigger DoWork_Event

Question

 BackgroundWorker worker = new BackgroundWorker();

        private void btn_Start_Click(object sender, EventArgs e)
        {
            worker.DoWork += new DoWorkEventHandler(worker_DoWork);
            worker.WorkerReportsProgress = true;
            worker.RunWorkerAsync();
        }

        private void worker_DoWork(object sender, DoWorkEventArgs e)
        {                
        using (WebClient webclient = new WebClient())
        {
            using (SPSite site = new SPSite(tb_sourceSite.Text))
            {
                using (SPWeb web = site.OpenWeb())
                {                        
                    webclient.Credentials = new NetworkCredential(tb_NC_Username.Text, tb_NC_Password.Text, tb_NC_Domain.Text);
                    SPList list = web.Lists[tb_sourceList.Text];

                    SPQuery qry = new SPQuery();
                    qry.Query = "<OrderBy><FieldRef Name='ID' /></OrderBy>";
                    qry.RowLimit = Convert.ToUInt32(NumberOfImages.Value);

                    SPListItemCollection items = list.GetItems(qry);

                    int i = 0;
                    progressBar1.Maximum = items.Count;
                    foreach (SPListItem item in items)
                    {
                        string filePathUrl = String.Concat(web.Url, "/", item.Url);

                        webclient.DownloadFile(filePathUrl, tb_DownloadFolder.Text);
                        worker.ReportProgress(i);
                        i++;
                    }
                }
            }
        }
        }

The Startbutton works, i can debug into it. But nothing happens in Backgroundworker. It doesn't download anything oder changes anything.

I am new to Backgroundworker. Am I doing something wrong?

Possible duplicate of [How to use a BackgroundWorker?](https://stackoverflow.com/questions/6481304/how-to-use-a-backgroundworker) — rs232, Nov 24 '17 at 09:25
@Julian - It's what I said - you can't update the UI from a non-UI thread, but you can use `ProgressChanged` to alert the UI to updates or you can `.Invoke(...)` on the UI thread with any UI control. — Enigmativity, Nov 24 '17 at 09:27
I think [this](https://www.codeproject.com/Articles/99143/BackgroundWorker-Class-Sample-for-Beginners) is a good example. — Nelson T Joseph, Nov 24 '17 at 09:29
I added the rest of my code maybe its some other mistake? I got that with the lables now but why doesn't the donwload work? — Julian, Nov 24 '17 at 09:30
It doesn't work even if I remove the lables / the UI changes The not UI changes dont work either — Julian, Nov 24 '17 at 09:55
@mjwills okay now the code in the question is the code i cant get working - I removed the labels — Julian, Nov 24 '17 at 10:18
`progressBar1.Maximum` You are still writing to UI controls in `worker_DoWork`. You can't do that. — mjwills, Nov 24 '17 at 10:19

score -1 · Answer 1 · answered Nov 24 '17 at 09:33

while debugging you might get cross-thread error. Try by creating a delegate to set label text. The below code is just a short example how to use BackgroundWorker with delegate.

 delegate void SetLabel(string msg);

 BackgroundWorker worker = new BackgroundWorker();

    private void btn_Start_Click(object sender, EventArgs e)
    {
        worker.DoWork += new DoWorkEventHandler(worker_DoWork);
        worker.WorkerReportsProgress = true;
        worker.RunWorkerAsync();
    }

    private void worker_DoWork(object sender, DoWorkEventArgs e)
    {
      this.Invoke(new SetLabel(SetLabelMethod), new object[]{     
       "Connecting..."})           
    }

    void SetLabelMethod(string msg)
   { 
     lbl_status.Text = msg;
   }

BackgroundWorker doesn't trigger DoWork_Event

1 Answers1