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At MWC today Nokia announced the Lumia 610 which is a lower spec device designed for emerging markets. This is running an updated Windows Phone OS which supports devices with just 256MB of RAM. To enable developers to create apps which support the new lower memory devices Microsoft are releasing an update to the Windows Phone SDK – 7.1.1.

At the moment a CTP has been released so that you can test your applications on a 256MB emulator but you should not install this to your main development machine as it doesn’t have a Go-Live license. To try out the new SDK you can download the CTP here:-

http://www.microsoft.com/download/en/details.aspx?displaylang=en&id=28962

There is just one API addition to support this change which is an additional property available from Microsoft.Phone.Info.DeviceExtendedProperties.GetValue – “ApplicationWorkingSetLimit” which will let you know whether you are running on a device with 256MB RAM. If your app/game is sufficiently resource heavy that you don’t feel it will run on such a device you can opt out so that your app/game will not be available on these lower powered devices. This is done by adding the Requirements element to your WMAppManifest.xml:-

<Requirements>
      <Requirement Name=”ID_REQ_MEMORY_90″ />
</Requirements>

The other main difference for these devices is there is no support for Background tasks – either Periodic or ResourceIntensive and attempting to add a background task on one of these devices will throw an InvalidOperationException – so it’s important to to check the capabilities first. Because of this limitation you need to design your app such that it doesn’t rely on a background task and that whatever sync/processing the task normally performs can be done when the app is running in the foreground.

Microsoft have prepared some information on optimising apps for 256MB and it is available here:-

http://msdn.microsoft.com/en-us/library/hh855081(v=vs.92).aspx

Some of the suggestions including using the built in launchers and choosers rather than running functionality such as the WebBrowser control or Bing Maps control within your app. They also suggest avoiding using the page transitions provided by the Silverlight Toolkit but don’t suggest an alternative – not sure if this means these devices don’t have the smooth page transitions at all or if they are suggesting that doing them from managed code is too resource intensive. You may decide to implement multiple approaches and use different methods depending on the device capabilities. Obviously the trick here is the balance between providing the best possible experience on each platform and avoiding adding too much more code to maintain.

Microsoft have published details of a new update (7.10.8107.79) which adds a number of fixes to the Mango release. It fixes the issue where the on screen keyboard will randomly hide itself which I’ve been finding frustrating recently and also a fix for the SMS bug which could disable messaging. It also hopefully finally resolves the issue when forwarding Exchange messages where the original message body would disappear. It hasn’t shown up yet but expect it over the next couple of weeks. Full details on all the updates and fixes are published here:-

http://www.microsoft.com/windowsphone/en-us/howto/wp7/basics/update-history.aspx

I’ve been working on an update to the Tasks application which adds in background synchronisation using the new background task support in Windows Phone 7.5. As with any app when you submit your XAP static analysis is performed on it to check, for example, that you have declared the correct capabilities based on the functionality in your app. Within a background agent you are only allow to call a subset of APIs – as you would expect you can’t play sound effects or draw to the UI (with the exception of toast notifications and tile updates). Because the main app has to include a reference to the dll which provides the background task, and the functionality within the dll is used in both the background task and the main app it made sense to move all of the logic into the background dll. This meant including a number of third-party references. I was very careful to ensure that nowhere in the background task was any restricted API called and it worked perfectly in testing.

The first problem is that upon submitting the static anaylsis looks at all of the referenced dlls and sees that they contain APIs not permitted in a background task and blocks the XAP. One of the culprits was InTheHand.Phone.dll (Part of Mobile In The Hand) because it provides a mixture of helper classes for logic and for UI. As I’ve been working on the 7.1 version in tandem I’ve now split this into two assemblies for Windows Phone 7.1 SDK projects. This means we can continue to use InTheHand.Phone in background tasks and add a reference to the second assembly in the main application only.

The second problem is that code within the sync logic calls ScheduledActionService.Add which is disallowed within a background task. This API is used within Tasks to add system-wide reminders (Another new feature for this version) for new task items. The code also has the ability to update and delete reminders based on modified or deleted tasks but these do not seem to have been flagged up as errors. This is a pain because it means that if the device syncs a new task with a reminder set to show before you next open the foreground app we won’t have had a chance to register it.

The other issue with the NeutralResourceLanguage is an issue with projects originally created with an older version of the development tools. You can add this setting from the projects properties, Application tab and click “Assembly Information…”.

This has been an interesting learning experience and shows that the validation picks up not just APIs used in the background agent code-path but also in referenced assemblies.