It works splendidly. The problem was that I had somehow undone my changes to the xaml for the style, and was using the old version instead of your new Workarounds version. You have more than answered my question, thank you sir.

Hi,

Could you explain how your scenario differs from this sample which shows all line segments as dotted for me:

App.xaml:

 <Application.Resources>
        <Style x:Key="lineStyle" TargetType="Line">
            <Setter Property="local:WorkArounds.StrokeDashArraySetter">
                <Setter.Value>
                    <local:StrokeDashArraySetter Value="5,1" />
                </Setter.Value>
            </Setter>
        </Style>
    </Application.Resources>

MainPage.xaml:

    <Grid x:Name="LayoutRoot" Background="White">
        <igChart:XamWebChart x:Name="chart1" Loaded="chart1_Loaded">
            <igChart:XamWebChart.Series>
                <igChart:Series ChartType="Line">
                    <igChart:Series.DataPoints>
                        <igChart:DataPoint Label="A" Value="1" />
                        <igChart:DataPoint Label="B" Value="2" />
                        <igChart:DataPoint Label="C" Value="3" />
                        <igChart:DataPoint Label="D" Value="4" />
                        <igChart:DataPoint Label="E" Value="5" />
                        <igChart:DataPoint Label="F" Value="4" />
                        <igChart:DataPoint Label="G" Value="3" />
                        <igChart:DataPoint Label="H" Value="2" />
                        <igChart:DataPoint Label="I" Value="1" />
                        <igChart:DataPoint  Label="J" Value="2" />
                        <igChart:DataPoint  Label="K" Value="3" />
                    </igChart:Series.DataPoints>
                </igChart:Series>
            </igChart:XamWebChart.Series>
        </igChart:XamWebChart>
    </Grid>

Code behind:

public partial class MainPage : UserControl
    {
        public MainPage()
        {
            InitializeComponent();
        }

        private void chart1_Loaded(object sender, RoutedEventArgs e)
        {
            foreach (DataPoint point in chart1.Series[0].DataPoints)
            {
                point.Style = (Style)Application.Current.Resources["lineStyle"];
            }
        }
    }

    public static class WorkArounds
    {
        public static readonly DependencyProperty StrokeDashArraySetterProperty =
            DependencyProperty.RegisterAttached(
            "StrokeDashArraySetter",
            typeof(StrokeDashArraySetter),
            typeof(WorkArounds),
            new PropertyMetadata(null,
                (o, e) => OnDataPointStylerChanged(o, e)));

        public static void SetStrokeDashArraySetter(
            DependencyObject target,
            StrokeDashArraySetter value)
        {
            target.SetValue(StrokeDashArraySetterProperty, value);
        }

        public static StrokeDashArraySetter GetStrokeDashArraySetter(
            DependencyObject target)
        {
            return (StrokeDashArraySetter)target
                .GetValue(StrokeDashArraySetterProperty);
        }

        private static void OnDataPointStylerChanged(
            DependencyObject o, 
            DependencyPropertyChangedEventArgs e)
        {
            var oldValue = e.OldValue as StrokeDashArraySetter;
            var newValue = e.NewValue as StrokeDashArraySetter;

            if (oldValue != null)
            {
                oldValue.Detach(o);
            }

            if (newValue != null)
            {
                newValue.Attach(o);
            }
        }
    }

    public class StrokeDashArraySetter
    {
        public string Value { get; set; }
        private DependencyObject _owner;

        internal void Attach(DependencyObject o)
        {
            if (_owner != null)
            {
                Detach(_owner);
            }
            var dep = o;
            if (dep == null)
            {
                return;
            }
            _owner = dep;

            if (_owner is Shape)
            {
                var shape = _owner as Shape;
                if (Value == null)
                {
                    return;
                }
                string[] vals = Value.Split(',');
                DoubleCollection coll = new DoubleCollection();
                foreach (var val in vals)
                {
                    double res;
                    if (double.TryParse(val, out res))
                    {
                        coll.Add(res);
                    }
                }
                shape.StrokeDashArray = coll;
            }
        }

        internal void Detach(DependencyObject o)
        {
            _owner = null;
        }
    }

-Graham

It's not null afterwards - and I did put that style in my app.xaml.

Something else interesting - if I place the style in <igWebChart:XamWebChart.Resources>, it only applies itself to the first line segment if it does not have a key name. Not really important, but I noticed it.

I only want to apply the dotted style to my series sometimes, so I need to be able to do it programmatically rather than having it explicitly set all the time. Sorry for the hassle, but I'm really hoping you can help me solve this. Thanks again.

make sure that point.Style is not null after that line, in other words.

I suspect you have your style defined at a lower level than App.xaml.

try: point.Style = (Style)Resources["dottedline"];