WPF从数据库冻结UI检索数据

Question

I have a problem with async retrieving data from database, everytime i get UI lock.

private async void RetrieveHotlist(object sender, RoutedEventArgs e) //button click
    {
        var hotItems = new ObservableCollection<HotItem>();
        await Task.Factory.StartNew(() =>
            {

                try
                {
                    var serv = "xxx";
                    string connStr = Common.GetConStrEF(serv + "\\" + Common.DBLOGIN_INSTANCE,
                                                        Common.DBLOGIN_DBNAME, Common.DBLOGIN_USER, Common.DBLOGIN_PASSWORD);
                    var dataModel = new xxxxDataModel(connStr);

                    foreach (var category in dataModel.SpecialNumberCategory)  //retrieving database CreateObjectSet<SpecialNumberCategory>("SpecialNumberCategory"); //ObjectContext
                    {
                        var item = new HotItem() {  Name = category.Name };
                        hotItems.Add(item);
                    }

                }
                catch (Exception exception)
                {
                    var baseException = exception.GetBaseException();
                    MessageBox.Show("Error\n\n" + exception.Message + "\n\n" + baseException.Message);
                }

            });
        if (Settings != null)
        {
            Settings.Hotlist.Clear();
            foreach (var hotItem in hotItems)
            {
                Application.Current.Dispatcher.BeginInvoke(DispatcherPriority.Background, new Action(() => Settings.Hotlist.Add(hotItem)));
            }
        }
    }

Why the RetrieveHotlist method locks my UI? And why await Task.Factory.StartNew() it's not enough?

Thanks for help :)

EDIT:

I deleted some code to be more clear.

private void RetrieveHotlist(object sender, RoutedEventArgs e) //button click
    {
        var b = new BackgroundWorker();
        b.DoWork += (o, args) =>
            {
                Thread.Sleep(2000); //**UI IS FULL RESPONSIVE FOR 2 sec.**
                var hotItems = new ObservableCollection<HotItem>();
                try
                {

                    var serv = "xxxx";
                    var dataModel = new xxxxDataModel(connStr);
                    var c = dataModel.SpecialNumberCategory; //**UI FREEZE / ENTITY FRAMEWORK**


        b.RunWorkerCompleted += (o, args) =>
            {

            };
        b.RunWorkerAsync();

    }

EDIT2: Thanks all for help, Entity Framework caused the issue ( i don't know why for now).

I replaced all model lines with SqlConnection and SqlCommand.Now it works great.

Answer 1

UI-related codes should be invoked on the UI-thread. Don't mix this with the same thread where you manipulate data (send, retrieve, update, etc.) to avoid deadlocks. On your case it was caused by the interaction with the database.

Here is an example:

 Application.Current.Dispatcher.Invoke(DispatcherPriority.Normal, new Action(() => { 
    /* Your code here */ 
    MessageBox.Show("Error\n\n" + exception.Message + "\n\n" + baseException.Message);
}));

Answer 2

Your method RetrieveHotlist() is blocking the UI cause below code

           foreach (var hotItem in hotItems)
            {
                Application.Current.Dispatcher.BeginInvoke(DispatcherPriority.Background, new Action(() => Settings.Hotlist.Add(hotItem)));
            }

is getting executed on main Thread . If you see closely the problem must be your are adding item one by one to the list and every time a item is added to your Hotlist it must be raising the change to UI , even if it's not doing it on every item add event happens, it will take some time to iterate a collection and add items to another collection , which is your freeze time of UI thread.

To avoid this you can directly assign the hotItems to Hotlist ( by using corresponding Ienumerable conversion). If you can give me type of Hotlist I can give you exact syntax. or you can prepare a temporary collection first of compatible type and then assign that collection to Hotlist . The key point is to minimize the work at UI thread. Replace whole foreach as below:

Application.Current.Dispatcher.BeginInvoke(DispatcherPriority.Background, new Action(() => Settings.Hotlist.AddRange(hotItems)));

and move the work done by foreach in your Thread . Now in the Action , either use AddRange() , do an assignment or anything to make it work.