Question

I have simple test (WPF – MVVM) client (for WCF oData service) app:

ViewModel

public class MainViewModel : ViewModelBase
{
    private MyEntities context;

    public ICollectionView Collection { get; private set; }

    private string searchString = "";
    public string SearchString
    {
        get { return searchString; }
        set
        {
            searchString = value;
            Collection.Refresh();
        }
    }

    public MainViewModel()
    {
        context = new MyEntities(new Uri("http://localhost:3780/Live.svc"));

        Collection = new CollectionView(context.Clients);
        //Collection = new CollectionView(context.Clients.ToArray());

        Collection.Filter = (o) => (o as Client).FullName.ToString().StartsWith(SearchString);
    }
}

and View

<ListBox ItemsSource="{Binding Collection}">
    <ListBox.ItemTemplate>
        <DataTemplate>
            <TextBlock Text="{Binding FullName}" />
        </DataTemplate>
    </ListBox.ItemTemplate>
</ListBox>

<TextBox Grid.Row="1" Text="{Binding SearchString, UpdateSourceTrigger=PropertyChanged}" />

I have two questions:

1. Why the movement of the ListBox slider slows down S_O___M_U_C_H (I
   have only 40 clients in the collection)?

2. Why, if I change this

   Collection = new CollectionView(context.Clients);
   

   to this

   Collection = new CollectionView(context.Clients.ToArray());
   

   so to break “connection” with the context through IEnumerable shell
   (it helps with UI performance problems) – stops working filtering! I
   do not understand why the disconnection of the collection from data
   context damage the filtering…

So, my final question is – is it possible to avoid GUI performance problems and at the same time implement filtering? And if so, how?

Any suggestions are welcome!

Answer 1

Ok, guys, I solved my problem. I should just pay attention to the message In the VS Output window:

Using CollectionView directly is not fully supported. The basic features work, although with some inefficiencies, but advanced features may encounter known bugs. Consider using a derived class to avoid these problems.

The solution was simple:

I changed this

Collection = new CollectionView(context.Clients);

to this

Collection = new ListCollectionView(context.Clients.ToList());

and then there are no GUI performance problems and filtering works as expected!

The result code was:

ViewModel:

public class MainViewModel : ViewModelBase
{
    private MyEntities context;

    public ICollectionView Collection { get; private set; }

    private string searchString = "";
    public string SearchString
    {
        get { return searchString; }
        set
        {
            searchString = value;
            Collection.Refresh();
        }
    }

    public MainViewModel()
    {
        context = new MyEntities(new Uri("http://localhost:3780/Live.svc"));

        Collection = new ListCollectionView(context.Clients.ToList());

        Collection.Filter = (o) => (o as Client).FullName.ToString().StartsWith(SearchString);
    }
}

and View:

<Grid x:Name="LayoutRoot"> 
    <Grid.RowDefinitions>
        <RowDefinition Height="*" />
        <RowDefinition Height="Auto" />
    </Grid.RowDefinitions>
    
    <ListBox ItemsSource="{Binding Collection}">
        <ListBox.ItemTemplate>
            <DataTemplate>
                <TextBlock Text="{Binding FullName}" />
            </DataTemplate>
        </ListBox.ItemTemplate>
    </ListBox>

    <TextBox Grid.Row="1" Text="{Binding SearchString, UpdateSourceTrigger=PropertyChanged}" />  
</Grid>

WCF Data Service:

public static void InitializeService(DataServiceConfiguration config)
{
    config.SetEntitySetAccessRule("*", EntitySetRights.All);
    config.SetServiceOperationAccessRule("*", ServiceOperationRights.All);
    config.DataServiceBehavior.MaxProtocolVersion = DataServiceProtocolVersion.V2;

    config.UseVerboseErrors = true; 
}