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Storing data on the client

From: Silverlight 5 Essential Training

Video: Storing data on the client

In this movie, I want to talk about storing data on the local computer; more explicitly, I want to show you how to store data in local files. The location for the files depends on several criteria. If you can get the user's explicit permission via the Open File dialog or the Save File dialog, your Silverlight app can write to local stories just like any other desktop application. Application files are commonly stored without a user prompt, however. Let's say you need to make a temporary file to store the audio stream from the user's microphone.

Storing data on the client

In this movie, I want to talk about storing data on the local computer; more explicitly, I want to show you how to store data in local files. The location for the files depends on several criteria. If you can get the user's explicit permission via the Open File dialog or the Save File dialog, your Silverlight app can write to local stories just like any other desktop application. Application files are commonly stored without a user prompt, however. Let's say you need to make a temporary file to store the audio stream from the user's microphone.

This temp file serves as a buffer or backup for the recording session. Saving this data into a file will happen without user intervention. Most operating systems restrict where an app can save files, and the operating system takes special precautions with web applications. Granting web applications unfettered access to the file system is sure to put your computer in jeopardy. To solve this dilemma, Silverlight uses isolated storage. Isolated storage provides a safe isolated file area.

By isolated, I mean that it is set aside from the normal user file path. Isolation also means that each Silverlight application gets its own secluded data store. So to summarize: you can store data and files on the local computer, either directly to the local hard drive with the user's permission or you can store to the hard drive without the user's permissions, which you can only use isolated storage. There is one other exception to the rule. If you run your application with elevated trust, you can access the users' documents folders--like their music and picture folder--without user involvement.

For this demonstration, I'm going to use a Visual Studio. I have opened a solution called StoringDataOnTheClient. This solution contains two projects: RememberingUserSettings and StoringDataOnTheClient. What I would like to do with this remembering user settings is to remember which one of these tabs the user has selected when they leave the Silverlight application. To do that, I had to write a little bit of code. Here I am wiring up an event handler for the TabControlSelectionChanged event.

When the user picks a new tab, my code will run in this method. One of things I like about Silverlight is that application-level settings are automatically stored in isolated storage. All I need to do is go to IsolatedStorageSettings.ApplicationSettings and provide a key value and then assign my piece of data. In this case, I am assigning the SelectedIndex of the tabControl. This FavTab is coming from here, this constant string value. Once, I put the information in there, I call save to persist to the hard drive.

Notice that I didn't have to check if the file exists first; Silverlight handles that for me. When the user comes back to my Silverlight application, the MainPage_Loaded event will fire. What I'm doing here is verifying that the application settings contains my information. If it is there, then I go in and get the information I stored, which was in integer value, and I place it in this variable. Once it's in the variable, I then assign it to this SelectedIndex of the tabControl. Let's see this in action.

Press F5 to run the application. I select the Adventure tab, and then I quit the application and restart it. Success! I'm now on the Adventure tab. Next, I'd like to talk about saving your own files, not just application-level settings. To do that, I'm going to go to the StoringDataOnTheClient project. I'm going to right-click on it and make it the StartUp Project, so that the next time I run the application it will use the correct project.

And then I'm going to go down and look at MainPage.xaml. My first demo is going to look at how you might save information into isolated storage. In this example, I am simulating the user clicking on the Save button. I'm going to come down here and get the location for the IsolatedStorage. I don't know the name of the directory where my files are stored, so I have to go to Silverlight and ask for the application store. That's what I'm doing here, GetUserStoreForApplication. So it's per my application, and it's per each user that is using my application.

Next, I check to make sure the directory in the isolated store exists. And if it does, I check for a file. If the file does not exist, then I create the file and then once I create the file, I do my normal file saving work here. Later, when I want to retrieve the information, I get the UserStoreForTheApplication, verify that the Directory and the FileExists, open the file, and then do my file retrieval. Remember, I said you could store in other locations as long as you ask the user for permission.

So let me show you how you would do that. Here is a button that's going to save to the local hard drive. I do that by creating a SaveFileDialog, setting a few properties, and then showing the dialog. If the user clicks OK, this will be equal to true. Next, I create a stream from the file, I create a writer to help write the information into the file, and then I call the WriteLine method to write the contents of the TextBox into the file. To read the information out, I ask the user permission by opening the file dialog. If they click OK and I have selected a file, then I open the file via a stream, create a reader to help me see the contents of the file, and then I call the reader.ReadToEnd method, and then I show the results in the MessageBox.

I can use this technique for images too. Down here, I am opening a file dialog, using the PNG or JPEG extensions. And the critical parts here are opening the stream, which will be, let's say a PNG file, I will create a brand new bitmap image. I'll get the source with the stream information here, I will set the source from the stream on the bitmap image, and then once I have the bitmap image, I can assign it as a source to any valid image control. Let's show this in action.

Click to save on the local system. I'll type a new note here, "This is my note," and click on Save. It prompts me to save it. I'm going to call this one demonote, and then I will click on Save. Next, to open it, I will click Open Notes. I will choose demonote and there you can see my text. For the last example, I will click on the Open Image from Local. I'm in my Documents folder. Here I have a png file called grapes.png. Click on Open and there it is.

In summary, I would like to repeat something I said earlier in the movie. You can store in the local file system as long as you get your users' permissions, where you are running in elevated trust. If you don't have this permission, you can store data only in isolated storage which offers a small but safe location for your data.

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This video is part of

Image for Silverlight 5 Essential Training
Silverlight 5 Essential Training

106 video lessons · 5394 viewers

Walt Ritscher
Author

 
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  1. 1m 41s
    1. Welcome
      53s
    2. Using the exercise files
      48s
  2. 35m 0s
    1. Overview of Silverlight
      3m 29s
    2. Setting up a developer computer
      2m 46s
    3. Installing the Silverlight Toolkit
      2m 21s
    4. Exploring the toolkit samples
      2m 35s
    5. Using Visual Studio 2010 to create a Silverlight project
      5m 10s
    6. Using Expression Blend to create a Silverlight project
      3m 13s
    7. Getting to know the Visual Studio interface
      8m 15s
    8. Working in the Expression Blend interface
      7m 11s
  3. 29m 46s
    1. Understanding the Visual Studio project structure
      3m 38s
    2. Creating a Silverlight page
      3m 17s
    3. Compiling your first application
      5m 0s
    4. Using other assemblies in an application
      5m 45s
    5. Deploying a Silverlight application
      3m 43s
    6. Understanding the startup process for an application
      3m 13s
    7. Understanding how users get Silverlight on their computers
      5m 10s
  4. 16m 59s
    1. Exploring the relationship between XAML and .NET
      3m 57s
    2. Using C#
      7m 16s
    3. Exploring the code-behind file
      5m 46s
  5. 43m 22s
    1. Working with XAML elements and Property attributes
      4m 56s
    2. Investigating XAML namespaces
      7m 31s
    3. Converting XAML properties with TypeConverters
      5m 1s
    4. Working with Property elements
      4m 24s
    5. Assigning runtime data with XAML markup extensions
      4m 21s
    6. Digging into the dependency property system
      6m 12s
    7. Creating a custom dependency property
      4m 42s
    8. Understanding attached properties
      6m 15s
  6. 9m 35s
    1. Debugging your code
      5m 17s
    2. Special Silverlight debugging techniques
      4m 18s
  7. 36m 0s
    1. Understanding layout
      4m 55s
    2. Using DockPanel and WrapPanel
      4m 2s
    3. Exploring sophisticated layouts with the Grid
      6m 40s
    4. Absolute positioning with the Canvas panel
      5m 20s
    5. Scrolling content with the ScrollViewer
      3m 28s
    6. Adjusting content alignment, margins, and sizing
      5m 6s
    7. Using the TabControl
      2m 17s
    8. Manipulating elements with transforms
      4m 12s
  8. 20m 32s
    1. Painting the user interface (UI) with SolidColorBrush
      6m 7s
    2. Getting colorful with gradient brushes
      3m 15s
    3. Decorating elements with ImageBrush
      4m 56s
    4. Creating effects with VideoBrush
      6m 14s
  9. 25m 42s
    1. Understanding routed events
      3m 12s
    2. Wiring up event handlers in Silverlight
      6m 4s
    3. Understanding event bubbling
      4m 39s
    4. Exploring mouse events
      7m 43s
    5. Exploring keyboard events
      4m 4s
  10. 32m 31s
    1. Displaying text on the screen
      3m 24s
    2. Gathering text input from the user
      5m 30s
    3. Showing complex text with RichTextBox
      6m 7s
    4. Understanding text overflow and text linking
      3m 14s
    5. Searching content with the AutoComplete type-ahead control
      6m 45s
    6. Using and embedding Silverlight fonts
      7m 31s
  11. 26m 47s
    1. Understanding content controls
      5m 7s
    2. Understanding button controls
      6m 16s
    3. Using the BusyIndicator
      4m 40s
    4. Showing tooltips
      4m 34s
    5. Changing content size with ViewBox
      1m 39s
    6. Exploring more controls
      4m 31s
  12. 55m 36s
    1. Connecting elements with binding
      9m 54s
    2. Using business data in a binding
      9m 21s
    3. Listing data with ItemsControls
      6m 39s
    4. Digging into the DataGrid
      8m 28s
    5. Using the DataForm
      3m 49s
    6. Storing data on the client
      7m 10s
    7. Debugging XAML bindings
      5m 41s
    8. Charting data
      4m 34s
  13. 24m 36s
    1. Creating an Out-of-Browser (OOB) application
      6m 16s
    2. Controlling aspects of an OOB application
      2m 49s
    3. Alerting the user with notification windows
      7m 13s
    4. Hosting HTML content in Silverlight applications
      8m 18s
  14. 30m 2s
    1. Exploring Silverlight trust levels
      3m 51s
    2. Creating an elevated trust application
      5m 57s
    3. Reaping the benefits of XAP signing
      6m 5s
    4. Making cross-domain calls
      5m 1s
    5. Getting started with COM Interop using the Speech API
      4m 21s
    6. Using COM Interop to interact with Microsoft Office
      4m 47s
  15. 16m 33s
    1. Showing child windows
      3m 48s
    2. Using a child window as a dialog window
      5m 7s
    3. Creating native windows
      2m 53s
    4. Maximizing a window with full screen mode
      4m 45s
  16. 13m 20s
    1. Dynamically loading UI content with user controls
      4m 46s
    2. Using the Navigation Framework
      8m 34s
  17. 9m 28s
    1. Using resource files
      3m 53s
    2. Using images in an application
      5m 35s
  18. 16m 32s
    1. Playing audio
      4m 27s
    2. Playing sound effects
      5m 4s
    3. Viewing video content with MediaElement
      4m 58s
    4. Changing video playback speed with TrickPlay
      2m 3s
  19. 14m 40s
    1. Capturing video with a web camera
      4m 16s
    2. Working with a microphone
      3m 47s
    3. Creating print output
      6m 37s
  20. 22m 35s
    1. Understanding Silverlight animations
      4m 35s
    2. Creating animations
      7m 52s
    3. Controlling animations
      4m 18s
    4. Simulating physics with animation easings
      5m 50s
  21. 27m 47s
    1. Placing XAML resources within a FrameworkElement
      6m 47s
    2. Centralizing settings in styles
      4m 8s
    3. Creating an alternate control UI with ControlTemplates
      6m 29s
    4. Dressing up your data with DataTemplates
      4m 33s
    5. Explaining the VisualStateManager: a simple way to manage control states
      5m 50s
  22. 10m 55s
    1. Handling global errors in a Silverlight application
      5m 46s
    2. Showing an application loading screen
      5m 9s
  23. 10m 48s
    1. Integrating with XNA
      7m 40s
    2. Exploring data analysis with PivotViewer
      3m 8s
  24. 1m 6s
    1. Goodbye
      1m 6s

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