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Operating with image files in a Windows Phone 7 application

· Mobile Zone

Images are one thing that is quite interesting to work with in a Windows Phone 7 application. In fact, for some specific applications manipulating image files can be a necessity (for example, when the application saves and loads edited photos).

As you probably already know, the files that are created by a Windows Phone 7 application are stored inside the isolated storage – a storage unit designated for the current application that no other application can access.

Unlike regular text files that can be read as plain string units, images are handled in a different way. Even if you used Silverlight before, opening image files in a Windows Phone 7 application will require you to use a different approach, since you won’t be directly in control of the storage space.

Basically, saving an image locally (for example, from a web site) is quite easy. If you’ve read my previous article on file handling , then I can say that the same principles are applied here.

To show an example, I am going to use a WebClient to download an image and store it locally.

WebClient client = new WebClient();
client.OpenReadCompleted += new OpenReadCompletedEventHandler(client_OpenReadCompleted);

I am referencing the OpenReadCompleted event handler that will be triggered when the data from the specified resource will be completely cached. Therefore, all I will have to do is store it for permanent access. Here is how the actual event handler looks like:

void client_OpenReadCompleted(object sender, OpenReadCompletedEventArgs e)
var resInfo = new StreamResourceInfo(e.Result, null);
var reader = new StreamReader(resInfo.Stream);

byte[] contents;
using (BinaryReader bReader = new BinaryReader(reader.BaseStream))
contents = bReader.ReadBytes((int)reader.BaseStream.Length);

IsolatedStorageFileStream stream = file.CreateFile("file.jpg");
stream.Write(contents, 0, contents.Length);

This way, I am converting the downloaded stream to a byte array and I am storing it in the root folder as a JPEG image. The actual image download is triggered via OpenReadAsync:

client.OpenReadAsync(new Uri("http://www.google.com/images/srpr/nav_logo14.png"));

Here I am passing a sample image URL (feel free to change it to whatever image you want). So it is downloaded and stored. Now it’s time to read the contents.

To test this, I inserted an Image control on the page that will display the stored image. To retrieve the image, an instance of IsolatedStorageFileStream is used:

IsolatedStorageFileStream stream = new IsolatedStorageFileStream("filet.jpg", FileMode.Open, file);

var image = new BitmapImage();

image1.Source = image;

Although the first thing that comes to mind would be using a relative URI for the image source, it will not work on a Windows Phone 7 application because the user has no direct control over the storage unit.


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