EvenTiles from Start to Finish–Part 14

In the previous episode of this series about how to develop a Windows Phone application from scratch we found out that special care must be taken when data must be passed between an application and its PeriodicTask. You learned how data can be protected against mutual access by using a Mutex object. You also learned that you cannot pass data directly from one to another, because the application and its PeriodicTask execute inside different processes.

In this episode of EvenTiles you will learn how you can make use of IsolatedStorage to pass data from the application to the PeriodicTask. Since we already created a separate project in the EvenTiles solution that is taking care of passing data, we can simply modify functionality in that project (EvenTilesComm) to use a file to pass data between the application and its PeriodicTask. Data protection against mutual access is already in place, so we can concentrate on file access. Hopefully the design decision in part 13 to make use of private methods that are called each time we access a public property inside the TileData class starts to make sense now.

What we want to achieve is the following:

  • From inside the application we can store a string containing content for the backside of a Secondary Tile in a file at any time
  • Our PeriodicTask executes approximately once per 30 minutes and it either displays the string passed by the application on the backside of the Secondary Tile or it displays a default string that is defined inside the PeriodicTask
  • The content of the backside of the Secondary Tile needs to toggle each time the PeriodicTask executes
  • If the EvenTiles user modifies the string to be displayed inside the Settings page, it will immediately be displayed on the Secondary Tile (if it exists)

In order to pass data between the application and the PeriodicTask we will extend the private retrieve / store methods inside the TileData class by adding a call to a couple of other private methods. Those new private methods will use a file in IsolatedStorage to read / write data from, meaning we can effectively pass data between the application and its PeriodicTask.

Properties to access Tile Data
  1. private static string RetrieveSecondaryBackContent()
  2. {
  3.     mtx.WaitOne();
  4.  
  5.     try
  6.     {
  7.         RetrieveTileContent();
  8.         return secondaryBackContent;
  9.     }
  10.     finally
  11.     {
  12.         mtx.ReleaseMutex();
  13.     }
  14. }
  15.  
  16. private static void StoreSecondaryBackContent(string content)
  17. {
  18.     mtx.WaitOne();
  19.  
  20.     try
  21.     {
  22.         secondaryBackContent = content;
  23.         PersistTileContent();
  24.     }
  25.     finally
  26.     {
  27.         mtx.ReleaseMutex();
  28.     }
  29. }

A new string to be displayed on the back side of a Secondary Tile will be stored by the application each time users modify their own tile text in the Settings Page of the EvenTiles application (something that will also be done initially when the application starts). The PeriodicTask simply retrieves that data (since now the data is persisted in a file this will work properly) and displays it on the back side of the Secondary Tile. Each time data needs to be stored a new file is created in IsolatedStorage or an existing file is overwritten. Each time data needs to be retrieved, we check if a file containing that data exists. There are small ways to optimize data access in the TileData class, because right now we simply read / write all file content when retrieving / storing single property values. However, this approach simplifies the code and the overhead with only two different variables is very small.

Using IsolatedStorage
  1. private const string contentFileName = "EvenTileContent.txt";
  2.  
  3. private static void PersistTileContent()
  4. {
  5.     using (var store = IsolatedStorageFile.GetUserStoreForApplication())
  6.     {
  7.         using (var contentStream = new StreamWriter(store.CreateFile(contentFileName)))
  8.         {
  9.             contentStream.WriteLine(showDefaultSecondaryBackContent.ToString());
  10.             contentStream.WriteLine(secondaryBackContent);
  11.         }
  12.     }
  13. }
  14.  
  15. private static void RetrieveTileContent()
  16. {
  17.     using (var store = IsolatedStorageFile.GetUserStoreForApplication())
  18.     {
  19.         if (store.FileExists(contentFileName))
  20.         {
  21.             using (var contentStream = new StreamReader(store.OpenFile(contentFileName, FileMode.Open)))
  22.             {
  23.                 showDefaultSecondaryBackContent = Convert.ToBoolean(contentStream.ReadLine());
  24.                 secondaryBackContent = contentStream.ReadToEnd();
  25.             }
  26.         }
  27.     }
  28. }

With the way we organized the functionality inside the TileData class in the previous episode of this development series, these are the only new methods necessary in order to pass data. When the user installs a Secondary Tile for the EvenTiles application and modifies its back string content through the Settings page, this is the result (changing the back content of the Secondary Tile every 30 minutes):

image

The following video shows EvenTiles in action with proper transfer of data between the application and its PeriodicTask.

Data transfer between an Application and a PeriodicTask through IsolatedStorage

To be able to experiment with this working implementation of EvenTiles, especially to understand how the application interacts with the PeriodicTask through a file in IsolatedStorage, the sample code is available for dowload here.

Right now we have the basic functionality of EvenTiles more or less ready, although the About Page still needs to get some content. That is something we will work on in the next part of EvenTiles. After that we will cover much more in the upcoming episodes of EvenTiles including but not limited to

  • using ads in the application
  • retrieving location information inside the application
  • taking pictures
  • modifying pictures
  • using alarms and notifications
  • using Visual Studio’s integrated Performance Analysis to find performance bottlenecks inside the application
  • submitting the application for certification

EvenTiles will continue soon so stay tuned for the next episode.

EvenTilesIf you want to see EvenTiles already in action on your Windows Phone, you can also install the latest version from Marketplace. Remember that this application is not meant to be extremely useful, although it contains similar functionality that “serious” applications have. Just go ahead and get your free copy of EvenTiles from Marketplace at this location: http://www.windowsphone.com/en-US/search?q=EvenTiles (or search on your phone for EvenTiles in the Marketplace application).

Advertisements
Both comments and trackbacks are currently closed.

Comments

  • Dave Erwin  On January 27, 2012 at 8:10 PM

    Maarten,

    I’m having a problem getting this to work. The periodic task is firing correctly but after it fires the first time the tile stops flipping. The tile blinks each time the periodic task fires after that so something is happening but I no longer see the back of the tile. Putting a breakpoint in OnInvoke the text is background content is changing but is never displayed.

    I thought it might be an emulator problem but it also does it when I install it on my phone. I downloaded the source from here and ran it and it does the same thing.

    Can you point me in the right direction to debug this? I’m out of ideas on where to look.

    Thanks for a great series, I’m learning alot from it.

    • Maarten Struys  On January 27, 2012 at 8:34 PM

      Dave,

      Did you try refreshing the start screen on the emulator (or the phone). The secondary tile spins usually three times, regardless of the periodic task updating the back side. By navigating away from the start screen and immediately returning to it, you have a way of spinning to restart again. The fact that the tile is not spinning continuously is something the operating system controls, in this way it is saving battery life.

      Maarten

      • Dave Erwin  On January 27, 2012 at 9:18 PM

        Maarten,

        Thank you. That took care of it. I thought it would restart the flip each time the text changed. But the battery life consideration makes sense.

        Any idea why the icon on secondary tile blinks each time the periodic task fires?

      • Maarten Struys  On January 28, 2012 at 4:29 PM

        Dave,

        I am pretty sure the blinking occurs because of replacing the tile content with new content in this particular code snippet (and thus again something we can’t really do much about):

        var newTileData = new StandardTileData
        {
            BackContent = showDefaultBackContent ? defaultBackContent : backContent
        };
        tileToFind.Update(newTileData);
        

        You have to keep in mind though that EvenTiles is sample code. In a ‘real’ scenario you might want to update the front of the tile, not the back. Updating the front of a (secondary) tile would also give that blinking experience, but since you then always immediately see the updated content, that will not be disturbing. And of course you don’t have to deal with refreshing the start screen if you are working with the front side of a tile.

      • Dave Erwin  On January 28, 2012 at 4:35 PM

        Maarten,

        Thanks again. That makes sense. All of these posts have been packed with great information.

Trackbacks

%d bloggers like this: