Windows Phone 8 : Other Ways of Launching Your App (part 2) - Using a File Association

To get started, you must modify the WMAppManifest.xml file as text. File associations use the application manifest file to specify the different file extensions. You can open the WMAppManifest.xml file as text by right-clicking the file and selecting View Code.

Just after the Tokens element, you must add a new element called Extensions. Inside the Extensions element, you will create a FileTypeAssociation element, as shown here:

<Deployment xmlns="..."
            AppPlatformVersion="8.0">
  <App ...>
    ...
    <Tokens>
      ...
    </Tokens>
    <Extensions>
       <FileTypeAssociation TaskID="_default"
                           Name="SAMPLE"
                           NavUriFragment="fileToken=%s">
        <Logos>
          <Logo Size="small"
                IsRelative="true">Assets/Logo33x33.png</Logo>
          <Logo Size="medium"
                IsRelative="true">Assets/Logo69x69.png</Logo>
          <Logo Size="large"
                IsRelative="true">Assets/Logo176x176.png</Logo>
        </Logos>
        <SupportedFileTypes>
          <FileType
            ContentType="application/sample">.sample</FileType>
        </SupportedFileTypes>
      </FileTypeAssociation>
    </Extensions>
    ...
  </App>
</Deployment>

The FileTypeAssociation element has several parts. First is a set of logos that are used in various parts of the operating system. You must specify all three logo sizes and supply them. The SupportedFileTypes element contains an extension name and the related ContentType. If you do not have a standard content type, you can use application/YOURAPPNAME. This means that you can now deal with the files that end in .foo. The FileTypeAssociation element’s NavigationUriFragment and TaskID attributes must both have the same values as is shown in the example.

When your application is launched, it will be executed with a special URI that contains information about the file that was launched.You’ll need to create a UriMapperBase derived class. Unlike the earlier example, though, the URI you’re looking for is /FileTypeAssociation:

public class AssociationMapper : UriMapperBase
{
  public override Uri MapUri(Uri uri)
  {
    var fileUri = uri.ToString();

    if (fileUri.Contains("/FileTypeAssociation"))
    {
      // Get the File Token
      var index = fileUri.IndexOf("fileToken=") + 10;
      var token = fileUri.Substring(index);

      // Create path to the XAML to Show File
      var path = string.Concat("/ShowFile.xaml?token=", token);

      return new Uri(path, UriKind.Relative);
    }
    else
    {
      // Let normal navigation happen
      return uri;
    }
  }
}

As you can see here, the operating system is passing in a query string value called fileToken that contains a token to the file that was launched. In this case we’re just post-pending it to the URI for the page we want to launch when a file is shown.

After you have created this new UriMapperBase derived class, you can register it with the application class as shown earlier in the protocol association example.

Back on the page that will handle the file, you can get that token from the query string and use it to interact with the file:

protected async override void OnNavigatedTo(NavigationEventArgs e)
{
  base.OnNavigatedTo(e);

  var token = NavigationContext.QueryString["token"];

  if (!string.IsNullOrWhiteSpace(token))
  {
    var fileName =
      SharedStorageAccessManager.GetSharedFileName(token);

    IStorageFile file = await
      SharedStorageAccessManager.
        CopySharedFileAsync(ApplicationData.Current.LocalFolder,
          fileName,
          NameCollisionOption.GenerateUniqueName,
          token);

      // ...

  }
}

After you’re in the OnNavigatedTo method of the page that is handling the file association, you can use the SharedStorageAccessManager class to get the name of the file by passing in the token. If you need the contents of the file, you can also use the CopySharedFileAsync to copy the file into a local folder (shown here as the ApplicationData.Current.LocalFolder). The CopyShareFileAsync copies the file into a location from which your application can access it and then returns an IStorageFile object that contains the file.