Updating UI with BackgroundWorker in WPF

Question

I am currently writing a simple WPF 3.5 application that utilizes the SharePoint COM to make calls to SharePoint sites and generate Group and User information. Since this process takes awhile I want to show a ProgressBar while the groups are being generated. The desired process is as follows:

1. User enters url and clicks button to fetch site data.
2. ProgressBar begins animation
3. Groups are generated and names are added to a ListView
4. Upon completion ProgressBar animation ends

The problem I am running into is that the UI is never updated. Neither the ProgressBar or the ListView makes any changes. If anyone has any ideas to help with the code below it would be greatly appreciated.

private void GetGroupsAndUsersButton_Click(object sender, RoutedEventArgs e)
{
    siteUrl = "";

    if (SiteURLTextBox.Text.Length > 0)
    {
        FetchDataProgressBar.IsIndeterminate = true;

        mWorker = new BackgroundWorker();
        mWorker.DoWork += new DoWorkEventHandler(worker_DoWork);
        mWorker.WorkerSupportsCancellation = true;
        mWorker.RunWorkerCompleted += new RunWorkerCompletedEventHandler(worker_RunWorkerCompleted);
        mWorker.RunWorkerAsync();
    }
    else
    {
        System.Windows.MessageBox.Show("Please enter a URL for the SharePoint site you wish to retrieve data");
    }
}

private void worker_DoWork(object sender, System.ComponentModel.DoWorkEventArgs e)
{
    siteUrl = SiteURLTextBox.Text;
    GroupListView.ItemsSource = null;

    try
    {
        using (SPSite site = new SPSite(siteUrl))
        {
            SPWeb web = site.OpenWeb();
            SPGroupCollection collGroups = web.SiteGroups;
            if (GroupNames == null)
                GroupNames = new List<string>();

            foreach (SPGroup oGroup in collGroups)
            {
                GroupListView.Items.Add(new ListViewItem() { Content = oGroup.Name });
            }

            foreach (ListViewItem item in GroupListView.Items)
            {
                item.MouseLeftButtonUp += item_MouseLeftButtonUp;
            }
        }
    }
    catch (Exception ex)
    {
        System.Windows.MessageBox.Show("Unable to locate a SharePoint site at: " + siteUrl);
    }
}

private void worker_RunWorkerCompleted(object sender, System.ComponentModel.RunWorkerCompletedEventArgs e)
{
    FetchDataProgressBar.Dispatcher.Invoke(System.Windows.Threading.DispatcherPriority.Normal,
    new Action(
        delegate()
        {
            FetchDataProgressBar.IsIndeterminate = false;
        }
        ));
}

Answer 1

At first you need to support ProgressChanged events. Update your BackgroundWorker initialization to:

GroupListView.ItemSource = null;
mWorker = new BackgroundWorker();
mWorker.DoWork += new DoWorkEventHandler(worker_DoWork);
mWorker.WorkerSupportsCancellation = true;
mWorker.WorkerReportsProgress = true;
mWorker.ProgressChanged += OnProgressChanged;
mWorker.RunWorkerCompleted +=
        new RunWorkerCompletedEventHandler(worker_RunWorkerCompleted);
mWorker.RunWorkerAsync(SiteURLTextBox.Text);

After that you have to add a OnProgressChanged handler:

private void OnProgressChanged(object sender, ProgressChangedEventArgs e)
{
    FetchDataProgressBar.Value = e.ProgressPercentage;
    ListViewItem toAdd = (ListViewItem)e.UserState;
    toAdd.MouseLeftButtonUp += item_MouseLeftButtonUp;
    GroupListView.Items.Add(toAdd);
}

Therefore you have to change your DoWork:

private void worker_DoWork(object sender, System.ComponentModel.DoWorkEventArgs e)
{
    BackgroundWorker worker = (BackgroundWorker)sender;            
    try
    {
        using (SPSite site = new SPSite((String)e.Argument))
        {
            SPWeb web = site.OpenWeb();
            SPGroupCollection collGroups = web.SiteGroups;
            if(GroupNames == null)
                GroupNames = new List<string>();
            int added = 0;
            foreach(SPGroup oGroup in collGroups)
            {
                added++;
                ListViewItem tmp = new ListViewItem() {
                    Content = oGroup.Name
                };
                worker.ReportProgress((added * 100)/collGroups.Count,tmp);
            }
        }
    }
    catch (Exception ex)
    {
        MessageBox.Show("Unable to locate a SharePoint site at: " + siteUrl);
    }
}

That's because you're not allowed to change GUI on DoWork.

After that, each ListViewItem is added separately to your ListView. I would also recommend, that your URL is passed as an argument to RunWorkerAsync.

Edit: Add percentage to OnProgressChanged.

Answer 2

In your DoWork method, you are manipulating WPF controls in code on a background thread, which you are not supposed to do. Actually, you should receive errors like "Cannot access control from other thread". Probably those exceptions are caught by your catch-all error handler, and maybe even the MessageBox doesn't work from the background thread.

As a quick fix, you would have to make siteURL and collGroups class fields, move everything before the using block to your GetGroupsAndUsersButton_Click method, and everything starting with the first foreach loop to the RunworkerCompleted event, so that all code which accesses controls runs on the UI thread.

Another thing you should change is that you should not create ListViewItems in code, but use a DataTemplate instead... this is not connected to your problem, though.

Answer 3

You'll need:

mWorker.WorkerReportsProgress = true;
mWorker.ProgressChanged += 
    new ProgressChangedEventHandler(worker_ProgressChanged);

Then in your DoWork you'll need to call:

var worker = (BackgroundWorker)sender;
worker.ReportProgress(progressAmount);

Good worked example here: http://msdn.microsoft.com/en-us/library/cc221403(v=vs.95).aspx