Question

I am trying to add Series binding to the Visifire graphing controls set. To this end i have created a SeriesSource dependency property of time DataSeriesCollection. This is bound in the front end using:

`<Chart SeriesSource={Binding Series} />`  

Problem
When the source changes, the validation callback is called. The value that is passed to this is the correct value, a populated ObservableCollection<something>. Immediately after the validate value is called, the CoerceValue callback is called by something, and the value that is sent to it is an EMPTY ObservableCollection<something>. Bounty will go to anyone who can:

1. Get the correct populated ObservableCollection<someting> passed to the CoerceValue callback OR
2. Get the correct value being passed to the OnSeriesSourceChanged callback OR
3. Explain to me how i can do any of the above 🙂

Here is the data template for the view:

<DataTemplate DataType="{x:Type vm:ReportViewModel}">
    <Grid Name="rootGrid">
    <visifire:Chart Grid.Row="1" SeriesSource="{Binding Series}">
        <visifire:Chart.AxesX>
                <visifire:Axis Title="X axis" />
        </visifire:Chart.AxesX>
        <visifire:Chart.AxesY>
                <visifire:Axis Title="Y axis" />
        </visifire:Chart.AxesY>
    </visifire:Chart>
    </Grid>
</DataTemplate>

Here is the target Dependency Property

    //Getter and setter for Dependency Property
    public ObservableCollection<DataSeries> SeriesSource
    {
        get { return (ObservableCollection<DataSeries>)GetValue(SeriesSourceProperty); }
        set { SetValue(SeriesSourceProperty, value);           }
    }

    // Using a DependencyProperty as the backing store for SeriesSource.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty SeriesSourceProperty =
        DependencyProperty.Register("SeriesSource", typeof(ObservableCollection<DataSeries>), typeof(Chart), new UIPropertyMetadata(new ObservableCollection<DataSeries>(), new PropertyChangedCallback(OnSeriesSourceChange), new CoerceValueCallback(CoerceSeries)), new ValidateValueCallback(ValidateSeriesSource));

    //Value validation callback
    private static bool ValidateSeriesSource(object value)
    {
        if (value as ObservableCollection<DataSeries> != null)
            return true;
        return false;
    }

    //Dependency Property Changed callback
    private static void OnSeriesSourceChange(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        Chart c = d as Chart;
        if (c == null)
            return;
        //This line was causing the issue. It was overriding the setter
        c.SeriesSource = (DataSeriesCollection)e.NewValue;
    }

    //Coerce Value callback
    private static object CoerceSeries(DependencyObject d, object value)
    {
        Chart c = d as Chart;
        var collection = value as System.Collections.ObjectModel.ObservableCollection<Visifire.Charts.DataSeries>;
        foreach (var item in c.Series)
        {
            if (!collection.Contains(item))
                c.Series.Remove(item);
        }
        foreach (var item in collection)
        {
            if (!c.Series.Contains(item))
                c.Series.Add(item);
        }
        return collection;
    }

New information
The value being received by the CoerceValue callback is ALWAYS the first value which that property was set to. So if the first value i pass it is a list with 1 item, it will always coerce the value back to a list with one item!

Edit: found the issue, it was in the property changed callback. Credit goes to Matt for helping me out with the CoerceValue callback

Answer 1

This may not be the exact problem, but you have logic in your setter. That code isn’t going to be executed when the property is assigned via a binding.

Instead of adding logic to your setter, consider using a “coerced” callback which gets called every time a value is assigned to your property. See here for more details about “coerce value” callbacks. They’re very similar to what you’ve done for your “property changed” callback.