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Question

What does Cannot modify the logical children for this node at this time because a tree walk is in progress mean?

Answer 1

A:

Apparently, some operation is being made that is changing a collection while it's being used. That's a big no-no.

Without analyzing the code further, that's all I can say.

Paulo Santos 2009-06-14 05:36:16

Answer 2

+2 A:

After playing around more, I think this is a bug in the Silverlight charting toolkit.

The following code causes a reproduceable crash.

int runCount = 0;
        private void bindChart(string searchString)
        {
           List<KeyValuePair<DateTime, int>> dataEmpty = new List<KeyValuePair<DateTime, int>>();

            List<KeyValuePair<DateTime, int>> dataFilled = new List<KeyValuePair<DateTime, int>>();
            dataFilled.Add(new KeyValuePair<DateTime, int>(DateTime.Today, 1));
            if (runCount == 0)
            {
                Chart1.DataContext= dataEmpty;
            }
            else
            {
                Chart1.DataContext = dataFilled;
            }
            runCount++;

        }

XAML:

<charting:Chart Grid.Row="0"
    Title="Title"
    LegendTitle="Legend" Name="Chart1" Grid.RowSpan="2">
            <charting:AreaSeries ItemsSource="{Binding}"

                                       DependentValuePath="Value"

                                       IndependentValuePath="Key"

                                       Background="Red" />


        </charting:Chart>

This will fail on the second call to bindChart.

Sean Turner 2009-06-14 06:15:48

Great work Sean!

Mark 2009-06-14 18:14:43

I filed a bug on CodePlex. It turns out this is a bug in the chart framework. See http://silverlight.codeplex.com/WorkItem/View.aspx?WorkItemId=3258 There is a workaround. Set teh chart's DataPointSeries Items source instead of the data context: (Chart1.Series[0] as DataPointSeries).ItemsSource = dataEmpty;

Sean Turner 2009-07-12 09:53:37

Answer 3

A:

I have the same problem. I am not using any background threads though. I just have a slider and on the ValueChanged event for the slider, I am recalculating and resetting the DataContext.

For example, A burn down chart. As the initial value changes, the graph updates automatically (essentially the Y axis of line series).

Changing the datacontext worked in the beta version of silverlight 3. Doesn't work in the release version. The above comment about setting (Chart1.Series[0] as DataPointSeries).ItemsSource works for me

Chaitanya 2009-07-16 06:22:11

Answer 4

+1 A:

Hej,

I've just had the error, and fixed it as well. The error also accoured when setting the datacontext.

I found that I had a selectionchanged-subscription on the list that was having its datacontext set. In this selectionchanged i was altering another property with notification support, which had a visual element binding on it.

Solved the problem by using the dispatcher for setting the property.

So try look for subscriptions on changes...

2009-08-25 13:01:59

ansaurus

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What does Cannot modify the logical children for this node at this time because a tree walk is in progress mean?

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