This blog post is part of a series about how Windows Phone 8.1 affects developers. This blog post talks about how to choose application model for your Windows Phone XAML app and is written by Johan Silfversparre at Jayway and was originally posted here.

Intro

The release of Windows Phone 8.1 SDK gives us, as developers, three different XAML app models to choose from for our future app development. This post will describe the difference between them and how to choose the right app model.

XAML app models

Windows Phone Silverlight 8 is the current app model your apps are using. Windows Phone Store is the new app model using a phone version of Windows RT. This convergence with the Windows 8.1 platform leads to a very similar, and in most case exact same, code for your Windows Store and Windows Phone Store apps. The Windows Phone Silverlight 8.1 app model is a merge of almost everything in Windows Phone 8 and at the moment more than 90% of the Windows Phone Store API.

Stay, upgrade or port

There are some things to consider when deciding to stay (Windows Phone Silverlight 8), upgrade (Windows Phone Silverlight 8.1) or port (Windows Phone Store) your existing app. This is also applicable when deciding app model for a new app. It is possible to have multiple variants of your app targeting different app models available in the Store at the same time. This allow you to keep a Windows Phone Silverlight 8 app available for users with devices not yet updated to WP 8.1 and also create and publish either a Windows Phone Store app or a Windows Phone Silverlight 8.1 app. Your current Windows Phone Silverlight 8 app will continue to work on both WP 8 and WP 8.1 devices. You can therefore stay on this app model if you don’t need to add any WP 8.1 features. Some features are only available in Windows Phone Silverlight 8.0 and 8.1. In these cases you have to stay or upgrade instead of porting to Windows Phone Store. Some Windows Phone Silverlight 8 features are changed and work different in Windows Phone Store. I will list them briefly here. Please read MSDN for a detailed list of the feature mappings. With the above information considered, a decision to stay on Windows Phone Silverlight 8, upgrade to Windows Phone Silverlight 8.1 or port to Windows Phone Store comes down to if you need to use any WP 8.1 features, if the app model supports the features you need and finally how much the Windows 8 and Windows Phone convergence in the Windows Phone Store app model is worth to you.

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