Relying on URIs that include the
full path to each page in your app can make your app brittle and
difficult to change the physical location of individual pages. If a
page is moved, all references to that file must be updated. This can
lead to maintainability issues as the size of the project grows.
The URI mapping system of Windows Phone apps
allows requests for a URI to be routed to a different URI, and uses a
single configuration point for the management of page URIs. Mapped URIs
can be made shorter and are, thus, less subject to typographical
errors. They also allow the exclusion of technology specific
information, such as the .xaml page file extension, making it easier to
retarget business logic for different platforms.
To use URI mapping, you must assign a System.Windows.Navigation.UriMapper instance to the UriMapper property of an app’s PhoneApplicationFrame. This can be done in XAML, as shown in the following excerpt from the App.xaml file in the downloadable sample code:
<Application
x:Class="DanielVaughan.WPUnleashed.Examples.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<Application.RootVisual>
<phone:PhoneApplicationFrame x:Name="RootFrame">
<phone:PhoneApplicationFrame.UriMapper>
<navigation:UriMapper>
<navigation:UriMapper.UriMappings>
<navigation:UriMapping
Uri="/ProductDetails/{productId}"
MappedUri="/Navigation/ProductDetailsView.xaml?productId={productId}" />
<navigation:UriMapping Uri="/WebBrowser/{url}"
MappedUri="/WebBrowser/WebBrowserView.xaml?url={url}" />
</navigation:UriMapper.UriMappings>
</navigation:UriMapper>
</phone:PhoneApplicationFrame.UriMapper>
</phone:PhoneApplicationFrame>
</Application.RootVisual>
<!-- Content omitted. -->
</Application>
The UriMapping class contains a Uri property and a MappedUri property. When navigation is requested from the Uri value, it is rerouted to the MappedUri property.
By using the curly brace syntax, as shown in
the previous excerpt, a substring of the requested URI can be
transplanted into the rerouted MappedUri
value. This is especially useful when you want to target the same page
using different URIs, and where the query string can be used to convey
the action to be undertaken by the page.
In the previous excerpt you see a UriMapping for the ProductDetailsView page. The ProductDetailsView
displays detailed information for a particular product, identified by a
query string parameter. When navigating to the ProductDetails page, if
the requested URL is /ProductDetails/2, this is rerouted to
/Navigation/ProductDetailsView.xaml?productId=2.
If you were to request the ProductDetailsView page using the NavigationService, as shown in the following example, the request would be rerouted accordingly:
NavigationService.Source = new Uri("/ProductDetails/2", UriKind.Relative);
The product to be displayed can then be determined in the ProductsDetailsView by reading the productId query string parameter, as demonstrated in the following excerpt:
protected override void OnNavigatedTo(NavigationEventArgs e)
{
base.OnNavigatedTo(e);
string productIdString = NavigationContext.QueryString["productId"];
int productId = int.Parse(productIdString);
ViewModel.LoadProduct(productId);
}
