CODEWITHSUNDEEP
c#wpfasynchronous.net-3.5
A191919
A191919

Reputation: 3462

DispatcherTimer WPF async

Every time when timer invoke UpdateDocumentsListFromServer UI freezes for 3 seconds. How to update list in async style under .net 3.5?

ViewModel:

public class ShippingDocumentsRegisterViewModel : ViewModelBase
    {
        ShippingDocumentsModel model = new ShippingDocumentsModel();

        DispatcherTimer timer = new DispatcherTimer();

        BackgroundWorker BW = new BackgroundWorker();

        public ShippingDocumentsRegisterViewModel()
        {
            timer = new DispatcherTimer();
            timer.Tick += new EventHandler(UpdateDocumentsListFromServer);
            timer.Interval = new TimeSpan(0, 0, 10);
            timer.Start();

            this.Columns = model.InitializeColumns();
            BW.DoWork += UpdateDocumentsList;
            BW.RunWorkerAsync();
        }

        public void UpdateDocumentsList(object o, EventArgs args)
        {
            this.ShippingDocuments = model.GetDocuments();
        }

        public void UpdateDocumentsListFromServer(object o, EventArgs args)
        {
            // Taking a lot of time. How to do it async?
            var tempDocuments = model.GetDocumentsFromServer();
            foreach (var item in tempDocuments)
            {
                this.shippingDocuments.Add(item);
            }
            //
        }

        private ObservableCollection<ShippingDocument> shippingDocuments;

        public ObservableCollection<ShippingDocument> ShippingDocuments
        {
            get
            {
                return shippingDocuments;
            }

            private set
            {
                shippingDocuments = value;
                RaisePropertyChanged("ShippingDocuments");
            }
        }

        public ObservableCollection<ShippingDocumentColumDescriptor> Columns { get; private set; }

    }

GetDocumentsFromServer look like 

    public ObservableCollection<ShippingDocument> GetDocumentsFromServer()
    {
        System.Threading.Thread.Sleep(3000);
        return new ObservableCollection<ShippingDocument> { new ShippingDocument { Name = "Test" } };
    }

Upvotes: 2

Views: 8346

Answers (4)

Kelly
Kelly

Reputation: 7193

Just offload it to a new thread using Task and Async/Await like so:

public async void UpdateDocumentsListFromServer(object o, EventArgs args)
        {
            // This will execute async and return when complete
            await Task.Run(()=>{
              var tempDocuments = model.GetDocumentsFromServer();
              foreach (var item in tempDocuments)
              {
                  this.shippingDocuments.Add(item);
              }
            });
            //
        }

Keep in mind this updates on a different thread then the UI. So it is not allowed to touch anything on the UI thread or you will get threading issues. So if shippingDocuments was created on the UI thread and is not thread-safe you could instead return a collection of items then add them:

public async void UpdateDocumentsListFromServer(object o, EventArgs args)
        {
            // Execute on background thread and put results into items
            var items = await Task.Run(()=>{
              var tempDocuments = model.GetDocumentsFromServer();                  
              return tempDocuments;
            });
            //add occurs on UI thread.
            this.shippingDocuments.AddRange(tempDocuments);
        }

Upvotes: 2

user6996876
user6996876

Reputation:

You could also use a background worker that reports progress to the UI

public ShippingDocumentsRegisterViewModel()
{

    BW.DoWork += UpdateDocumentsListFromServer;
    BW.RunWorkerCompleted += BW_RunWorkerCompleted;

    BW.WorkerReportsProgress = true;
    BW.ProgressChanged += UpdateGui;
    BW.RunWorkerAsync();
}
public void UpdateGui(object o, EventArgs args)
{
    foreach (var item in tempDocuments)
    {
        this.shippingDocuments.Add(item);
    }
}
public void UpdateDocumentsListFromServer(object o, EventArgs args)
{

    while (true) {
        System.Threading.Thread.Sleep(3000);

        tempDocuments = GetDocumentsFromServer();
        BW.ReportProgress(0);

    }
}

int num = 0;
public ShippingDocument[] GetDocumentsFromServer()
    {
        System.Threading.Thread.Sleep(3000);
        return new ShippingDocument[1] { new ShippingDocument { Name = "Test" + num++} };
    }

private ShippingDocument[] tempDocuments = new ShippingDocument[0];

Upvotes: 2

Gopichandar
Gopichandar

Reputation: 2842

As mentioned in comment, you can make use of Timers instead of DispatcherTimer. DispactherTimer will access the UIThread where as Timer use different thread from threadpool.

Also, you can dispatch an action to UIThread from different thread 

Application.Current.Dispatcher.BeginInvoke(new Action(() =>
           {
               //Do some UI stuffs                   
           }));

Hope that helps.

Upvotes: 0

brunnerh
brunnerh

Reputation: 185553

Use a regular Timer and only dispatch the access to shippingDocuments.

Upvotes: 0

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