ColumnSeries from Silverlight Charting Toolkit problems

Question

Hi,

I'm new to Silverlight development and am currently venturing into the Charting territory. I've been following several tutorials that show how easy it is to bind a ColumnSeries to a datasource using ItemsSource (http://silverlight.net/forums/t/44166.aspx).

I'm programatically adding a chart to a canvas.

Chart BudgetChart = new Chart { Title = "budget", MaxHeight= 200, MaxWidth=500};
ColumnSeries cs = new ColumnSeries();
BudgetChart.Series.Add(cs);
cs.Title = "blarg";
cs.ItemsSource = o.Budget; //returns List<Budget>
cs.IndependentValueBinding = new System.Windows.Data.Binding("Budget");
cs.DependentValueBinding = new System.Windows.Data.Binding("Year");

This code compiles fine. However, when I debug it, this error is throw However, I've been experiencing a lot of difficulty with ItemsSource. Each time I assign the ItemsSource, I get a error stating that it's Sys.InvalidOperationException: ManagedRuntimeError error #4004 in control 'Xaml1': System.NullReferenceException System.NullReferenceException: Object not set to an instance of an object. at System.Windows.Control.DataVisualization.Charting.ColumnSeries.<>c__DisplayClass8.b__4()

Please help, this error is driving me crazy!!!

Answer 1

Try moving the ItemsSource assignment to after the bindings. Also Add the series to the chart after having configured its bindings.

Chart BudgetChart = new Chart { Title = "budget", MaxHeight= 200, MaxWidth=500};
ColumnSeries cs = new ColumnSeries();
cs.Title = "blarg";
cs.IndependentValueBinding = new System.Windows.Data.Binding("Budget");
cs.DependentValueBinding = new System.Windows.Data.Binding("Year");

BudgetChart.Series.Add(cs);

cs.ItemsSource = o.Budget; //returns List<Budget>

Answer 2

I've finally learned how to read. I was binding wrongly. I got confused between the Dependent and Independent bindings. Thank you for your help AnthonyWJones.

Answer 3

Make sure your first data point does not contain a null/Nothing in the dependent value. The error occurs when the chart tries to "sniff" the type of dependent axes required, and fails.

   at System.Windows.Controls.DataVisualization.Charting.DataPointSeriesWithAxes.GetAxes(DataPoint firstDataPoint, Func`2 independentAxisPredicate, Func`1 independentAxisFactory, Func`2 dependentAxisPredicate, Func`1 dependentAxisFactory)

at System.Windows.Controls.DataVisualization.Charting.ColumnSeries.GetAxes(DataPoint firstDataPoint)

There seems to be no workaround. One option is to subclass a LinearAxis which overrides CanPlot(value). Currently NumericAxis.CanPlot fails for value==null

 /// <summary>
    /// Returns a value indicating whether a value can plot.
    /// </summary>
    /// <param name="value">The value to plot.</param>
    /// <returns>A value indicating whether a value can plot.</returns>
    public override bool CanPlot(object value)
    {
        double val;
        return ValueHelper.TryConvert(value, out val);
    }