WP7 ListPicker - How to mark selected item in model when generated from DataSource?

Question

I have a Menu object (set as the DataContext) which contains many Options (Menu.Options), which contains a Name (Option.Name) and many Options (Option.Options). The collections are all of type ObservableCollection<T>.

The Menu is loaded from an XML file, so the amount of Options and Values can vary.

To help visualise, here is the relevant XAML:

<ListBox ItemsSource="{Binding Path=Options}">
    <ListBox.ItemTemplate>
        <DataTemplate>
            <StackPanel>
                <!-- Title -->
                <TextBlock Text="{Binding Path=Name}" TextWrapping="Wrap" Style="{StaticResource PhoneTextExtraLargeStyle}" />
                <!-- Selection -->
                <toolkit:ListPicker ItemsSource="{Binding Path=Options}" SelectionChanged="ListPicker_SelectionChanged">
                    <toolkit:ListPicker.ItemTemplate>
                        <DataTemplate>
                            <TextBlock Text="{Binding Path=Name}" />
                        </DataTemplate>
                    </toolkit:ListPicker.ItemTemplate>
                    <toolkit:ListPicker.FullModeItemTemplate>
                        <DataTemplate>
                            <TextBlock Text="{Binding Path=Name}" />
                        </DataTemplate>
                    </toolkit:ListPicker.FullModeItemTemplate>
                </toolkit:ListPicker>
            </StackPanel>
        </DataTemplate>
    </ListBox.ItemTemplate>
</ListBox>

I have a method ListPicker_SelectionChanged on the SelectionChanged event, in which I want to somehow mark the current selection in the databound model. I need to do it using just the parameters supplied to the method, as each ListPicker is generated at runtime. So I can't be specifying actual control names (as far as I'm aware anyway).

I can see two possible options:

1) To have a CurrentSelection inside Menu.Option, where I can put a reference to the last selected item for that ListPicker

2) To have a Selected attribute on the Option.Option. Downside here though is making sure all elements are deselected when a new one is selected.

I've tried browsing the object tree of sender, but anything I find, such as ItemsHost, is inaccessible (private/protected).

Is there any way I can achieve a solution?

Answer 1

Option 1 is the better one, use TwoWay binding on the ListPicker.SelectedItem.

<phone:PhoneApplicationPage 
    x:Class="StackOverflowWP7.SO9369491"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:phone="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone"
    xmlns:shell="clr-namespace:Microsoft.Phone.Shell;assembly=Microsoft.Phone"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:toolkit="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone.Controls.Toolkit"
    xmlns:local="clr-namespace:StackOverflowWP7.SO9369491_"
    mc:Ignorable="d" d:DesignWidth="480" d:DesignHeight="768"
    FontFamily="{StaticResource PhoneFontFamilyNormal}"
    FontSize="{StaticResource PhoneFontSizeNormal}"
    Foreground="{StaticResource PhoneForegroundBrush}"
    SupportedOrientations="Portrait" Orientation="Portrait"
    shell:SystemTray.IsVisible="True">
    <phone:PhoneApplicationPage.DataContext>
        <local:Menu>
            <local:Menu.Options>
                <local:Option Description="Size">
                    <local:Option.Options>
                        <local:Option local:Description="Large" />
                        <local:Option local:Description="Regular" />
                    </local:Option.Options>
                    <local:Option.CurrentSelection>
                        <local:Option local:Description="Regular" />
                    </local:Option.CurrentSelection>
                </local:Option>
            </local:Menu.Options>
        </local:Menu>
    </phone:PhoneApplicationPage.DataContext>
    <!--LayoutRoot is the root grid where all page content is placed-->
    <Grid x:Name="LayoutRoot" Background="Transparent">
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>

        <!--TitlePanel contains the name of the application and page title-->
        <StackPanel x:Name="TitlePanel" Grid.Row="0" Margin="12,17,0,28">
            <TextBlock x:Name="ApplicationTitle" Text="MY APPLICATION" Style="{StaticResource PhoneTextNormalStyle}"/>
            <TextBlock x:Name="PageTitle" Text="page name" Margin="9,-7,0,0" Style="{StaticResource PhoneTextTitle1Style}"/>
        </StackPanel>

        <!--ContentPanel - place additional content here-->
        <Grid x:Name="ContentPanel" Grid.Row="1" Margin="12,0,12,0">
            <ListBox ItemsSource="{Binding Path=Options}">
                <ListBox.ItemTemplate>
                    <DataTemplate>
                        <StackPanel>
                            <!-- Title -->
                            <TextBlock Text="{Binding Path=Description}" TextWrapping="Wrap" Style="{StaticResource PhoneTextExtraLargeStyle}" />
                            <!-- Selection -->
                            <toolkit:ListPicker ItemsSource="{Binding Path=Options}"
                                                SelectedItem="{Binding CurrentSelection, Mode=TwoWay}" >
                                <toolkit:ListPicker.ItemTemplate>
                                    <DataTemplate>
                                        <TextBlock Text="{Binding Path=Description}" />
                                    </DataTemplate>
                                </toolkit:ListPicker.ItemTemplate>
                                <toolkit:ListPicker.FullModeItemTemplate>
                                    <DataTemplate>
                                        <TextBlock Text="{Binding Path=Description}" />
                                    </DataTemplate>
                                </toolkit:ListPicker.FullModeItemTemplate>
                            </toolkit:ListPicker>
                        </StackPanel>
                    </DataTemplate>
                </ListBox.ItemTemplate>
            </ListBox>
        </Grid>
    </Grid>

</phone:PhoneApplicationPage>

Here's the Code Behind

namespace StackOverflowWP7
{
    using Microsoft.Phone.Controls;

    public partial class SO9369491 : PhoneApplicationPage
    {
        // Constructor
        public SO9369491()
        {
            InitializeComponent();

        }

    }

}

namespace StackOverflowWP7.SO9369491_
{
    using System.Collections.ObjectModel;
    using System.Linq;

    public class Menu : Option
    {
        public Menu()
            : base("Main Menu")
        {
        }
    }

    public class Option
    {
        public Option() {}

        public Option(string Name, params string[] choices)
        {
            this.Description = Name;
            foreach (var choice in choices)
            {
                this._options.Add(new Option(choice));
            }
        }

        public string Description { get; set; }

        private ObservableCollection<Option> _options = new ObservableCollection<Option>();
        public ObservableCollection<Option> Options { get { return _options; } }

        private Option _CurrentSelection;

        public Option CurrentSelection
        {
            get { 
                return _CurrentSelection; 
            }
            set
            {
                if (_options.Contains(value))
                {
                    _CurrentSelection = value;
                }
                else
                {
                    _CurrentSelection = _options.FirstOrDefault((o) => o.Description == value.Description);
                }
            }
        }

    }

}