Question

Hi I’m trying to update a line chart every second (from the wpf data visualisation toolkit). The following code works for a PieChart:

VB:

Private Sub Window_Loaded(sender As System.Object, e As System.Windows.RoutedEventArgs) Handles MyBase.Loaded
    '  DispatcherTimer setup
    Dim dt As DispatcherTimer = New DispatcherTimer()
    AddHandler dt.Tick, AddressOf dispatcherTimer_Tick
    dt.Interval = New TimeSpan(0, 0, 1)
    dt.Start()
End Sub

Public Sub dispatcherTimer_Tick(ByVal sender As Object, ByVal e As EventArgs)
    UpadateChartData()
    Chart1.DataContext = ""
    Chart1.DataContext = ChartData
End Sub

Public Sub UpadateChartData()
    Dim r As Integer = GetRandom(1, 10)
    ChartData.Add(New ChartData() With {.Name = r.ToString, .Votes = r})
End Sub

XAML:

 <chartingToolkit:Chart Name="Chart1" Title="Chart1" Width="400" Height="400" >
        <chartingToolkit:LineSeries ItemsSource="{Binding}" IndependentValueBinding="{Binding Path=Name}" DependentValueBinding="{Binding Path=Votes}" />
</chartingToolkit:Chart>

But I get this error when I use LineSeries (or any other type of chart):

Cannot modify the logical children for this node at this time because a tree walk is in progress.

Can anyone tell me why I’m getting the error or suggest an alternative approach?

Thanks for any help!

Answer 1

It indeed appears to be a bug in the toolkit, as ColinE mentioned.

I would suggest to take a look at Dynamic Data Display, which really facilitates these kind of things and makes it very easy. They provide a few new objects like ObservableDataSource<T>, and on this you can call source.AppendAsync(Dispatcher, T) which will update the graph.