Question

When the list underlying my databound DXGrid is updated, the scrollbar of the grid updates but the body of the grid does not, at least not right away. As soon as I click on the grid scrollbar, the body does refresh.

To illustrate – here is my application in the initial state:

When I add four new objects to my underlying list, only the scrollbar changes:

Finally, when I press on the “down” button at the bottom of the scrollbar, the entire grid refreshes:

Expected behaviour: The grid should refresh properly whenever the underlying database list is updated, not much later when the user tries to interact with the list.

The Xaml for my GridControl looks like this:

    <dxg:GridControl dxlc:DockLayoutControl.Dock="Client" 
                     ItemsSource="{Binding Project.TimeSeries}">

        <dxg:GridControl.Columns>
            ... omitted ...
        </dxg:GridControl.Columns>
        <dxg:GridControl.View>
            <dxg:TableView Name="tableView1"
                           AllowEditing="False"
                           AllowColumnFiltering="True"
                           ShowAutoFilterRow="True"
                           ShowGroupPanel="False" 
                           FocusedRow="{Binding SelectedTimeSeries, Mode=TwoWay}"/>
        </dxg:GridControl.View>
    </dxg:GridControl>

DataContext of the form is set to a TimeSeriesPresenter:

public class TimeSeriesPresenter : ITimeSeriesPresenter
{
    public TimeSeriesPresenter(ITimeSeriesVisual view)
        : base(view) { ... }

    public BuilderProject Project 
        { get { ... } set { ... } }

    public TimeSeriesDefinition SelectedTimeSeries 
        { get { ... } set { ... } }

and a BuilderProject looks like this:

public class BuilderProject : ViewModelBase
{
    public IList<TimeSeriesDefinition> TimeSeries
    { get { ... } }
    ...
}

Both of these objects implement INotifyPropertyChanged and the properties are triggering the PropertyChanged event properly. So, everything should just work, right?

Clearly the DXGrid is receiving some kind of update from the view model, because the scrollbar changes. But why doesn’t it repaint entirely?

Is there some kind of “mode” required for a DXGrid to do DataBinding normally?
What am I missing?

Update

All of my data objects inherit from ViewModelBase which implements the INotifyPropertyChanged interface. In addition to TimeSeriesPresenter and BuilderProject (shown above), here’s a summary of TimeSeriesDefinition:

public class TimeSeriesDefinition : ViewModelBase
{
    public string SeriesID
    {
        get { return mSeries; }
        set { 
            if (!Equals(mSeries, value) {
                mSeries = value;
                OnPropertyChanged("SeriesID");
            }
        }
    }
    ... etc ...
}

Answer 1

The source of the problem was this code:

public class BuilderProject : ViewModelBase
{
    public IList<TimeSeriesDefinition> TimeSeries
    { get { ... } }
    ...
}

Even though IList<T> should be supported, in practice its not.

The requisite fix was to change to using ObservableCollection<T> instead:

public class BuilderProject : ViewModelBase
{
    public ObservableCollection<TimeSeriesDefinition> TimeSeries
    { get { ... } }
    ...
}

In my case, this led to parallel maintenance of two lists – an underlying IList<> in the presentation agnostic model, and an ObservableCollection<> in the ViewModel. Keeping the two lists in sync is a bit of overhead, but not hard to get right.