MVVM Silverlight and page navigation

Question

I'm just starting out with Silverlight and also with the MVVM model. When performing page navigation and sending arguments from one page to another, .. is the use of querystring the most accepted method?

It seems to be a big confusion on how passing arguments while performing page navigation should be performed. At least I find several topics about this on various web resources, but no one seems to agree upon a "best practice" method.

Answer 1

NOTE: The below solution of using query strings in the NavigationContext works for both in and out of browser.

You normally set your UriMapper something like this:

           <navigation:Frame Source="/Home" >
                <navigation:Frame.UriMapper>
                    <uriMapper:UriMapper>
                        <uriMapper:UriMapping Uri="" 
                                   MappedUri="/Views/Home.xaml"/>
                        <uriMapper:UriMapping Uri="/{pageName}/{key}" 
                                   MappedUri="/Views/{pageName}.xaml?entityGuid={key}"/>
                        <uriMapper:UriMapping Uri="/{pageName}" 
                                   MappedUri="/Views/{pageName}.xaml"/>
                    </uriMapper:UriMapper>
                </navigation:Frame.UriMapper>
            </navigation:Frame>

And then to get the NavigationContext into the view model, you add a helper to your View like so:

<navigation:Page xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                 xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                 xmlns:helpers="clr-namespace:MyApp.Helpers"
                 xmlns:navigation="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Navigation"
                 DataContext="{Binding Path=Entity, Source={StaticResource Locator}}"
                 helpers:Navigator.Source="{Binding}">

And then you have an attached property helper like so (I modified this from someone else, though I forgot who):

using System.Windows;
using System.Windows.Controls;

namespace MyApp.Helpers
{

    public interface INavigable
    {
        System.Windows.Navigation.NavigationService NavigationService { get; set; }
        System.Windows.Navigation.NavigationContext NavigationContext { get; set; }
    }


    public static class Navigator
    {
        public static INavigable GetSource(DependencyObject obj)
        {
            return (INavigable)obj.GetValue(SourceProperty);
        }

        public static void SetSource(DependencyObject obj, INavigable value)
        {
            obj.SetValue(SourceProperty, value);
        }

        public static readonly DependencyProperty SourceProperty =
             DependencyProperty.RegisterAttached("Source", typeof(INavigable), typeof(Navigator), new PropertyMetadata(OnSourceChanged));

        private static void OnSourceChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            Page page = (Page)d;

            page.Loaded += PageLoaded;
        }

        private static void PageLoaded(object sender, RoutedEventArgs e)
        {
            Page page = (Page)sender;

            INavigable navSource = GetSource(page);

            if (navSource != null)
            {
                navSource.NavigationService = page.NavigationService;
                navSource.NavigationContext = page.NavigationContext;
            }
        }
    }
}

And then add the following to your ViewModel:

    private NavigationContext _NavigationContext;
    public NavigationContext NavigationContext {
        get { return _NavigationContext; }
        set {
            if (_NavigationContext == value)
                return;
            _NavigationContext = value;
            RaisePropertyChanged("NavigationContext");
        }
    }
    protected override void RaisePropertyChanged(string propertyName) {
        base.RaisePropertyChanged(propertyName);

        switch (propertyName) {
            case "NavigationContext":
                if (NavigationContext.QueryString.ContainsKey("entityGuid")) {
                    if (NavigationContext.QueryString["entityGuid"].Equals("new", StringComparison.InvariantCultureIgnoreCase)) {
                        LoadNewEntity();  // your 'new' logic
                    } else {
                        this.EntityGuid = new Guid(NavigationContext.QueryString["entityGuid"]);
                        LoadExistingEntity(EntityGuid);  // your 'existing' logic
                    }
                }
                break;
        }
    }