Tag Archives: IsolatedStorage

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).

EvenTiles from Start to Finish–Part 6

In the previous episode of this series about how to develop a Windows Phone application from scratch we used IsolatedStorage to persist some data. Since IsolatedStorage is a file store on a Windows Phone device, for exclusive use by a single application, it can be a challenge to look at its contents. Luckily, the Windows Phone 7.1 SDK has a tool available to explore IsolatedStorage contents. In this episode of EvenTiles we will explore this Isolated Storage Explorer Tool.

The Isolated Storage Explorer Tool is a command line tool, which is installed together with the Windows Phone 7.1 SDK in the following folder:

C:\Program Files (x86)\Microsoft SDKs\Windows Phone\v7.1\Tools (64 bit OS)
or
C:\Program Files\Microsoft SDKs\Windows Phone\v7.1\Tools (32 bit OS)

The tool itself has a lot of parameters, to get contents from IsolatedStorage, to write contents to IsolatedStorage, to specify an application and to specify a device. In a command prompt some limited help information is available:

image

In order to retrieve our ApplicationSettings from IsolatedStorage for EvenTiles, the first thing we need to know is the ProductID for our application. This ide can be found in the WMAppManifest.xml file.

WMAppManifest.xml
  1. <Deployment xmlns="http://schemas.microsoft.com/windowsphone/2009/deployment" AppPlatformVersion="7.1">
  2.   <App xmlns="" ProductID="{883385e6-52e5-4835-83db-8a17499b5767}" Title="EvenTiles"

The next thing we need to do is make sure that the Emulator is started (or a physical device is connected). Either should have the application installed, but it is not necessary to have the application running. After passing the following command,

image

the folder C:\iso will contain a snapshot of our application’s IsolatedStorage.

image

When we drag and drop the _ApplicationSettings file to Visual Studio 2010, you can see that its contents are XML data, representing a Dictionary with one single entry defined in it, matching our Secondary Tile’s back side string.

image

You might not like using a command line tool to explorer IsolatedStorage. In that case, there is good news for you. If you browse to http://wptools.codeplex.com/, you will find the Windows Phone Power Tools for download. This handy collection of tools embeds the different SDK tools including the Isolated Storage Explorer Tool inside a Windows application. With that application you can explore your application’s IsolatedStorage as well. Using the power tool, it is also easy to write new or modified files to your application’s IsolatedStorage. The latter makes a lot of sense if you want to test new versions of applications against old contents in IsolatedStorage, for instance to migrate old files to new versions.

image

The following video shows the Isolated Storage Explorer Tool and the Windows Phone Power Tools in action.

Using the Isolated Storage Explorer Tool and the Windows Phone Power Tools

So this time we did not add functionality to our EvenTiles application, but it is important to learn about useful tools to help us develop our applications as well. In the next episode we will talk about Tombstoning and Fast Application switching and what we need to do in our application to support these two important execution states on Windows Phone devices.

imageIf you want to see EvenTiles already in action on your Windows Phone, you can install the latest release from Marketplace. Remember that this application is not meant to be extremely useful, although it contains similar functionality that “serious” applications have. All functionality that you can find in the released version of EvenTiles will be covered in the upcoming episodes of this blog series, together with all source code. 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).

EvenTiles from Start to Finish–Part 5

In episode number four of this series about how to develop a Windows Phone application from scratch we created the SettingsPage using a combination of Expression Blend and Visual Studio 2010. The SettingsPage has limited functionality, but it can modify a string that will eventually be displayed on the backside of a Secondary Tile. In this episode we will take a look at how to store data in IsolatedStorage.

If you watched the video of episode 4 you have noticed that the string containing the text to be eventually displayed on the Secondary Tile’s backside was not saved when the application was closed, because a default string showed up when the application was started again. In order to store the string so it will be available when the application starts again, we are going to store it into a specific part of the our IsolatedStorage. IsolatedStorage can be used to store files and system settings. It just acts as a hard drive with one little but important difference. IsolatedStorage is …. isolated. Everything that is stored in IsolatedStorage is exclusively available for the application that owns it, so other applications can not access it.

When a Windows Phone application starts, it will be running in the foreground, with its MainPage visible. As long as the user is working with the application, it remains n the foreground. An application can be terminated by the user by pressing the Back key on the phone until the last page of the application will be closed. An application can also be moved to the background. This happens when the user activates another application, or for instance when the user answers a phone call. On starting, a Launching event is raised. The App.xaml.cs file already has event handlers defined for the Launching and Closing events. These are the events that we are going to use to store / retrieve our string containing the backside text for our Secondary Tile.

NOTE: The sample code, retrieving and storing data in the Launching / Closing event works fine. However, all code executing upon firing those events has a time limit of 10 seconds. If an event handler takes longer to execute, the application will be immediately terminated. If you have much data to store / retrieve, you should take an alternative approach. You can for instance make use of a separate thread in those situations to retrieve / store information. To keep our sample lean and mean, we will directly retrieve / store data into IsolatedStorage from within the Launching / Closing event handlers.

Since all functionality is already available inside the SettingsPage to store the backside text of the Secondary Tile, we are only adding some functionality to the App.xaml.cs file. First thing to do is get access to the IsolatedStorageSettings for our application, which is in fact a dictionary in which values can be stored / retrieved through a key. The IsolatedStorageSettings are implemented as a singleton and are created the first time we try to access them. IsoloatedStorageSettings can be accessed from inside our entire application, although right now we will only use IsolatedStorageSettings inside the App.xaml.cs file.

IsolatedStorageSettings
  1. public const string DefaultSecBackContent = "Having an even # of tiles on my StartScreen";
  2. public const string keyActSecBackContent = "K_ASBC";
  3.  
  4. public static string ActualSecBackContent { get; set; }
  5.  
  6. private IsolatedStorageSettings appSettings = IsolatedStorageSettings.ApplicationSettings;

In the code snippet you can see a declaration of a key (just a string variable) that is used to store / retrieve the string containing content for the back side of a Secondary Tile. You can also see how a private variable is declared that is initialized with the one and only instance of our application’s settings in IsolatedStorage.

Application_Launching
  1. // Code to execute when the application is launching (eg, from Start)
  2. // This code will not execute when the application is reactivated
  3. private void Application_Launching(object sender, LaunchingEventArgs e)
  4. {
  5.     if (!appSettings.Contains(keyActSecBackContent))
  6.     {
  7.         appSettings[keyActSecBackContent] = DefaultSecBackContent;
  8.     }
  9.     ActualSecBackContent = (string)appSettings[keyActSecBackContent];
  10. }

Each time the application is started, the Application_Launching method will be executed. In this method we check if an object is stored under the key keyActSecBackContent. If this is not the case, we create a new entry in the dictionary of application settings and assign it with a default text that can be written to the back side of the Secondary Tile. If an entry already exists (which is basically always after creating one during the very first time), we retrieve the actual string from that entry. Since an application settings dictionary stores objects, we need to cast the actual value to a string.

When the application is terminated, the contents of the string that contains the text for the back side of the Secondary Tile might have been changed in the SettingsPage. That is the reason why we store that string always when the application ends.

Application_Closing
  1. // Code to execute when the application is closing (eg, user hit Back)
  2. // This code will not execute when the application is deactivated
  3. private void Application_Closing(object sender, ClosingEventArgs e)
  4. {
  5.     appSettings[keyActSecBackContent] = ActualSecBackContent;
  6. }

It looks like we now have stored our application settings properly. However, that is not entirely the case, since our application might be temporarily interrupted because the user can start other applications without terminating our application. In those situations we have to take a look at the life cycle of an application. That will be topic of another episode of EvenTiles. It is also interesting to take a look at exactly what information is stored in IsolatedStorage. In order to do that, you can make use of the Isolated Storage Explorer Tool, a handy little tool that will be covered in episode six of EvenTiles.

In the following video you can see all the steps that you need to make application settings persistent and to retrieve them each time the application starts again.

Using IsolatedStorage to store ApplicationSettings

Note: Every now and then I will make sure that you can download all source code that we created so far. I strongly recommend you to do so and to start experimenting with that code. After all, looking at real code, modifying it and understanding your modifications will hopefully help you to become a great Windows Phone developer fast.

If you want to keep up with the code of EvenTiles that is available until now, you can download it as a Zip file from this location. After downloading and unzipping it, you can open the EvenTiles solution in Visual Studio 2010 Express for Windows Phone. You must have the Windows Phone SDK 7.1 installed on your development system to do so. If you have a developer unlocked phone you can deploy the application to your phone, if you don’t have a developer unlocked phone you can still experiment with this application inside the emulator.