WinRT Event Handling from DataTemplate - winrt-xaml

Question

I have a DataTemplate which requires an event handler for one of the objects. This DataTemplate is contained in a ResourceDictionary. What is the best way to add an event handler to this template?
I tried defining the event handler in app.xaml.cs but the handler isn't executing. Creating a code behind file for the ResourceDictionary leads to load errors during app start up in MergedDictionaries.
from GraphStyles.xaml
<DataTemplate x:Key="PieTemplate">
<Grid HorizontalAlignment="Left" Width="350" Height="350" >
<Border>
<Charting:Chart
x:Name="PieChart"
Title="Play Attempts"
Margin="70,0" Loaded="PieChart_Loaded">
<Charting:Chart.Series>
<Charting:PieSeries
Title="Attempts"
ItemsSource="{Binding Items}"
IndependentValueBinding="{Binding Name}"
DependentValueBinding="{Binding Value}"
IsSelectionEnabled="True" />
</Charting:Chart.Series>
</Charting:Chart>
</Border>
</Grid>
</DataTemplate>
in App.Xaml.cs
private void PieChart_Loaded(object sender, RoutedEventArgs e)
{
var pieChart = sender as Chart;
var legendItems = ((PieSeries)pieChart.Series[0]).LegendItems;
foreach (LegendItem item in legendItems)
{
pieChart.LegendItems.Add(item);
pieChart.LegendStyle = item.Style;
}
}

Answer 1

Option 1
As far as I am aware you will have to reference the datatemplate in the page/usercontrol's Resources at the top. Use a merged dictionary so you can still utilize the graphstyles.xaml.
If you are uncomfortable as this breaks your convention, there is a rather long winded alternative:
Option 2
Use an MVVM Viewmodel and set the page/usercontrols DataContext.
Keep the datatemplate in the graphstyles.xaml and use an Attached Behavior to hook the Loaded event, passing the event trigger up to the viewmodels command.
Create an event in the ViewModel that the UI can respond to, then hook onto that and handle in the Views codebehind as you have done.
I must say I'm not mad on Option 2 as it kind of breaks some view/VM seperation but it should get the job done - note that you will have to pass the chart as an object through from the attached behavior, to the viewmodel then back to the view against before you cast it back to a Chart.