My XAML Navigation System in Layers

Layer 1: the Frame

At the core of my stinky onion is the Frame control, hosted in a UserControl. I prefer to have one Frame per application, which implies that the UserControl is my conventional Client control (Microsoft culture has called this Main or Home—in the ASP.NET MVC space). Anyway, because I call my default visual “Client”, the navigation frame is called ClientFrame:

<navigation:Frame x:Name="ClientFrame"
    BorderThickness="0">
    <navigation:Frame.UriMapper>
        <uriMapper:UriMapper>
            <uriMapper:UriMapping Uri="" MappedUri="/Views/IndexPage.xaml"/>
            <uriMapper:UriMapping Uri="/" MappedUri="/Views/IndexPage.xaml"/>
            <uriMapper:UriMapping Uri="/{key}/{id}" MappedUri="/Views/{key}Page.xaml"/>
            <uriMapper:UriMapping Uri="/{key}" MappedUri="/Views/{key}Page.xaml"/>
        </uriMapper:UriMapper>
    </navigation:Frame.UriMapper>
</navigation:Frame>

This declaration comes with several implications:

• The only content to be loaded in a Frame is a System.Windows.Controls.Page. To need an exception to this rule suggests that the application is getting too complex.
• The default Page is IndexPage.xaml. This strongly suggests that this page is some kind of human-readable summary of the application domain.
• Every Page name in the application should end with ‘Page.’
• Visuals representing the Domain can be located by a “key” or a key with an ID.

It is my intent that all of these keys should be stored in NavigationBookmarkData (see below).

Layer 2: Frame Eventing in Code Behind

My PasteBin.com code sample shows (almost) all of the eventing required for a navigation Frame. The table below summarizes:

Layer 3: NavigationBookmarkData

Back in 2012, in “Silverlight Page Navigating with MVVM Light Messaging and Songhay NavigationBookmarkData,” I went into detail about this class definition. Another PasteBin.com sample for this class is available.

Layer 4: Handling NavigatingCancelEventArgs

It’s the NavigationBookmarkData that can be used to determine whether a Navigation should or should not be cancelled. My ClientViewModel has concerns for Messaging and Navigating. Messaging logic supports the LightNavigationMessage<NavigatingCancelEventArgs> sent by Client UserControl. Navigating logic handles this ‘light-navigation’ message by evaluating it with the NavigationBookmarkData. A rough sketch of the handler illustrates:

void HandleClientNavigating(LightNavigationMessage<NavigatingCancelEventArgs> message)
{
    navigationBookmarks.SetBookmarkContext(message.TargetLocation);
    string category = (message.RelativeUriSegments.Length > 1) ?
        message.RelativeUriSegments[1] : null;
    int? id = (message.RelativeUriSegments.Length > 2) ?
        FrameworkTypeUtility.ParseInt32(message.RelativeUriSegments[2]) : null;
    if(category == "category1" && id.HasValue) this.DoRiaOperationGetMyData(id.Value);
    else if(navigationBookmarks.IsBookmarkUnknown()) message.Content.Cancel = true;
    else throw new NotImplementedException("Page is not yet supported.");
}

First the handler puts the navigating location in ‘context’ so the NavigationBookmarkData can ‘validate’ it. The LightNavigationMessage class contains logic to split the navigating location into an array of RelativeUriSegments (see PasteBin.com listing). This array can contain a key and/or ID, according to the conventions declared on Layer 1, the ClientFrame.

When we have "category1" and an ID we can then call the RIA service (in DoRiaOperationGetMyData()). The navigation system built into the .NET Framework (on Level 1) will display the page at the navigating target location. This page of course contains visuals bound to the data returned by the RIA operation.

However, when it is clear that the “bookmark” (or the navigation target location) set in context is unknown (if(navigationBookmarks.IsBookmarkUnknown())), then the navigation is cancelled.

Layer 5: Actually Doing the Navigation

MVVM Commanding is what starts the funky Navigation going through each layer of our onion. The commanding eventually reaches logic that looks like this:

void DoNavigation(string category, int id)
{
    var format = this._bookmarks.GetPatternForGetDataFormat();
    var bookmark = string.Format(format, category, id);
    HtmlPage.Window.NavigateToBookmark(bookmark);
}

So Layer 1 uses what comes in the box with the .NET Framework and Layer 5, with its call to HtmlPage.Window.NavigateToBookmark(), is also using what ships from Microsoft. Or should I say what shipped from Microsoft?

The “death” of Silverlight in general strongly suggests that HtmlPage.Window.NavigateToBookmark() is dead (while the Frame lives on) in particular.

Related Links

((PhoneApplicationFrame)Application.Current
        .RootVisual).Navigate(...);

https://github.com/BryanWilhite/