Andrej Tozon's blog

In the Attic


Windows Phone 8.1 – LocalCacheFolder

In one of my talks at recent NT konferenca I talked about some of the new ways of working with application data in Windows Phone 8.1. With all the exciting additions to the latest Windows Phone 8.1 APIs, the best news around application data in those new APIs is that they are now (mostly) aligned with the Windows Runtime (WinRT), so Windows 8 developers can pick up on them immediately and transition their work to the new platform, share code, etc.

With the aligned data APIs, Windows Phone 8.1 applications (both Silverlight and Runtime) can now store their data into one of the following folders:

  1. LocalFolder – a local folder, used for storing application data, it’s persistent across application updates and gets backed up to the cloud. This folder was already available in Windows Phone 8 and it’s the same folder as Isolated Storage known from Windows Phone 7.
  2. TemporaryFolder – also a local folder, but its space is managed by the OS. Whenever the system detects it’s running low on storage space, it will start deleting files in temporary so don’t ever strongly depend on files stored in this folder. It makes a perfect place for storing cached web responses or images that can be recreated any time. This folder does not participate in backups.
  3. RoamingFolder – files, stored in this folder, will roam across devices, meaning those files will be synchronized over the cloud whenever possible. Perfect for settings and/or small chunks of state (i.e. for continuous clients). When roaming is disabled on the device, those files (and settings) will get backed up as well. The storage space is limited to 100kB – if application goes over that quota, the synchronization stops (until the total usage falls back under roaming storage quota).


But wait - there’s one more folder in Windows Phone 8.1, that’s available in Windows Phone 8.1 API only. Even more, unlike some other APIs that are present on both Windows and Windows Phone and will throw an exception when used from the wrong platform, this one is completely hidden from Windows. Using it from a shared project, you have to #ifdef it out of Windows platform and include in Windows Phone build only:

    var localCache = ApplicationData.Current.LocalCacheFolder;

So what is it? Is it used for caching? Well, not exactly (though it might, but I prefer the TemporaryFolder for that).

The LocalCacheFolder is almost exactly like the good old LocalFolder, with one single, but important exception – unlike LocalFoder, the files written to this folder will never be backed up to the cloud and will always stay on the device it was originally written at. Good for storing some (semi) sensitive information or pieces of state you don’t want or need to restore later.

And while I mentioned sensitive data, there’s one more thing worth mentioning - the best place to store sensitive data is into the Credential Locker (represented by the PasswordVault class), a familiar class from WinRT APIs, that is now also available to Windows Phone 8.1 – YAY!


To finish up, here’s a quick recap – use PasswordVault for storing sensitive information, LocalCacheFolder for data you don’t want ever to leave that particular phone, TemporaryFolder for temporary, easy-to-recreate data, RoamingFolder for settings and small state to synchronize across devices, and LocalFolder for main application data that gets backed up to the cloud (and, of course – restored).

Enable automatic daylight / night mode switch with your Windows Phone 8.1 app

Sample source code is available for download.

You know those fancy car GPS navigators that automatically switch color mode to dark when it gets dark to make it easy on your eyes? The display even turns dark when you drive into a tunnel and lights back up when you’re out…

Well, with ambient-light sensor support in the latest Windows Phone 8.1 SDK, it’s possible to build something quite like that. The new API is quite straightforward and follows the same practice as with other device sensors.

When your app starts, you should first query the device for the sensor to see if it exists. The GetDefault() method will return null if sensor isn’t present on the device or the system was unable to get a reference to it (happens when device is in a connected standby):

var sensor = Windows.Devices.Sensors.LightSensor.GetDefault();
if (sensor == null)

Once having access to the sensor, it’s recommended to set its reporting interval to default value, but in cases where you need to set it explicitly, you can do it by changing sensor’s ReportInterval, but check you’re not going below MinimumReportInterval. Here’s the code for setting it to 5 minutes, but if you need more dynamic readings, just leave it at default:

sensor.ReportInterval = Math.Max(sensor.MinimumReportInterval, 5*60*1000);

[Note: don’t forget to set it back to default – 0 – when you’re done]

To start reading, you can either perform a one-time read:

var reading = sensor.GetCurrentReading();

… or subscribe to continuous reads (with read interval set earlier):

sensor.ReadingChanged += OnLightSensorReadingChanged;

Either way, you’ll get a LightSensorReading with information about the current reading. The illuminance level returned by this is in lux so it should be easy to compare with some known values. I figured 500 – 1000 would be a good value to detect a decent daylight and in this example I’m testing against a value of 1000 lux.

We have the ambient light level, now what?

There are various cases where light sensor could come in handy, here’s a couple:

1. Allow user to have it’s theme respond to light, e.g. have light theme during the day and dark theme during the night. Reading apps, for example.
Luckily, in Windows Phone 8,1, changing theme for a page (or for any specific element) is now very simple. No more 3rd party helpers. Here’s an example of a OnLightSensorReadingChange event handler for the case, where application theme will be according to the latest sensor reading:

void OnLightSensorReadingChanged(Windows.Devices.Sensors.LightSensor sender, Windows.Devices.Sensors.LightSensorReadingChangedEventArgs args)
        () => RequestedTheme = args.Reading.IlluminanceInLux < 1000
              ? ElementTheme.Dark
              : ElementTheme.Light

[Notice the relevant line is wrapped in a Dispatcher call – the LightSensorReadingChanged event will always be fired on a background thread so we have to get back to the UI thread to set a visual property properly]

2. Any app that displays a map could use this feature. Navigation apps, locators, running apps, …
And the Map control has a vary handy property to support this, let’s have a look at Map’s ColorScheme:

void OnLightSensorReadingChanged(Windows.Devices.Sensors.LightSensor sender, Windows.Devices.Sensors.LightSensorReadingChangedEventArgs args)
        () =>  Map.ColorScheme = args.Reading.IlluminanceInLux < 1000
               ? MapColorScheme.Dark
               : MapColorScheme.Light;

One final note – the same API is available to Windows Store apps as well. Build for both, it’s great Smile

Download sample source code.

Launch Windows Phone 8.1 Podcasts app from your app

Latest Windows Phone update, called Windows Phone 8.1 will bring us a new app for managing podcasts. The Podcasts app, similar to what we previously had in Music+Videos hub’s podcasts section, will let users subscribe to their favorite shows to be played later on.

The good things for developers here is a fact that we’ll be able to integrate the new app in our applications’ workflow by launching the Podcasts app by one of the following URI schemes: itpc:, pcast: and podcast:.

For example, this is how you launch the Podcast app:

await Launcher.LaunchUriAsync(new Uri("podcast:"));

But it doesn’t end here. By specifying an Url pointing to a specific podcast feed, the app will fetch that feed and display podcast overview page and make it easy for the user to subscribe to that feed. Here’s an example of how to make it display the Hanselminutes feed:

await Launcher.LaunchUriAsync(new Uri(""));


Fun fact: the above screenshot was taken from my phone (device) using the Project my screen app, which was released today. Read more about it here.

Upon launching the app, the user has quick access to playing the latest episode (Podcasts app supports streaming) or subscribe to the series.

When user is done with subscribing or playing podcasts, navigating back will get her back to your app where she can continue her work with it.

Of course other apps can now move to supporting those URI protocols as well so, each user could choose her favorite podcast app to integrate with on her device.

Windows 8.1. Developers Contest–rok za prijavo podaljšan!


Rok za prijavo aplikacij v prvem valu je podaljšan do 6. aprila, rok za drugi krog prijav pa je 30. april!

Za vas Imamo dobre novice! J Na podlagi mnogih vprašanj, ki smo jih dobili o registraciji aplikacij in pravočasni odobritvi za Windows Store, smo prestavili rok za registracijo za en teden, tako da lahko v prvem valu prijavite vaše aplikacije do 6. aprila.

Naslednji koraki:

  • Aplikacije, registrirane v prvem valu (do 6. aprila), bodo dobile povratno informacijo in podporo pri izboljšanju uporabniškega vmesnika ter UX. Tako boste lahko izboljšali in ponovno naložili vaše aplikacije do 30. aprila. Seveda boste lahko nabrali tudi več prenosov in si s tem izboljšali možnosti za nagrade.
  • Vsi razvijalci, ki še niste uspeli narediti in objaviti aplikacij v prvem ciklu, jih boste lahko prijavili v drugem ciklu (do 30. aprila) in tekmovali za nagrade, a brez povratne informacije in dodatne podpore za izboljšanje uporabniške izkušnje.

Razdelitev nagrad:

16 Nokia Lumia 1520 bomo podelili zmagovalcem kategorij:

  • Najboljši UX design (lokalna kategorija)
  • Regionalne kategorije:
    • Najboljši UX design;
    • Največkrat prenesena aplikacija;
    • Največkrat ocenjena aplikacija;
    • Najbolje ocenjena aplikacija;

30 Prestigio Multipad Visconte Windows tablic bomo razdelili zmagovalcem vseh ostalih kategorij.


Več informacij o tekmovanju ter pravila najdete na spletni strani tekmovanja. Pridružite se tudi Facebook skupini, kjer bomo odgovorili na vaša vprašanja, tam boste dobili tudi vse dodatne informacije. Oglejte si brezplačne predloge za aplikacije in materiale z Windows 8 dogodka!

Še vedno je čas – ne zamudite priložnosti!