Windows Phone 8 - 11 App to App Communication

Editor's Notes

• #3: This session is about File and Protocol Associations.It is perhaps erroneously referred to as ‘App to App’ communication, which although being one of the interesting things you can do with it, is not the *only* thing.It’s about some interesting ways you can launch your app to handle specific files that are being sent to it, or because an app or the shell has ‘opened’ a particular custom URI that your app is registered to handle.
• #4: You can use file and URI associations in Windows Phone 8 to automatically launch your app when another app launches a specific file type or URI scheme. When launched, a deep link URI is used to send the file (a reference to the file) or URI to your app. You can also use the association launching API to launch another app in the same way.File associations allow your app to automatically launch when the user wants to open a particular file. That file could come from a variety of sources including, but not limited to: an email attachmenta website via Internet Explorera Near Field Communications (NFC) taganother app from the StoreA URI association allows your app to automatically launch when another app launches a special URI. What makes that URI special is that it begins with a URI scheme name that your app has registered for. The URI scheme name is the portion of the URI that comes just before the colon (‘:’).
• #5: How association works for the user When the user launches a file or URI from an app, what happens next depends on which apps are installed on the phone. If no apps on the phone can handle that particular file or protocol association, the user will be given the option to get one that does.When there is only one app on the phone registered for a particular file or protocol association, that app will be automatically launched when the user wants to open it. If a user has more than one app on their phone registered for a file or protocol association, each time the user opens the file, they will be as asked which app they want to use.Tip: Don’t register for a file or protocol association unless you can perform a useful action with it. If your app causes the app menu to be shown frequently, the user may choose to uninstall it altogether to avoid having to always make a choice.
• #6: Like Windows 8, Windows Phone 8 uses Launcher..::..LaunchFileAsync(IStorageFile) to launch a file and Launcher..::..LaunchUriAsync(Uri) to launch a URI. However, the way Windows Phone XAML apps receive a file or URI is different. Also, Windows Phone does not have a “default” Store app. If there are multiple Store apps installed that can handle a particular file or URI association, the user chooses the receiving app from a menu.
• #7: For demonstration notes please look in the “Demonstration” folder and open the corresponding Word document.
• #9: To handle a particular file type, register for a file association in the app manifest file. Your app can specify any file association that it is able to handle. However, any file associations that are reserved by built-in apps will be ignored (we’ll look at what those are a little later).To provide an “integrated” look to custom file types appearing in built-in apps, you have the option of supplying logos (image files) to appear beside the files. For example, if a file (of your custom type) were attached to an email message, a small logo would appear beside the attachment after it was downloaded. The table on the slide lists the three image sizes that you can provide for each file association.
• #10: You can specify a number of elements in a FileTypeAssociation:Extensions - Must follow the Tokens element.FileTypeAssociation -Describes a file association. You can register a maximum of 20 file associations. The Name attribute is required, but you choose your own friendly name. Specify the TaskID and NavUriFragment elements as shown.Logos - Lists all logos for a file association. This is optional when no logos are specified. You must provide all sizes (small, medium, large) if you provide any.SupportedFileTypes - Lists all file extensions that are associated with the file type.FileType - Lists the file extension that is associated with the file type, including the period (‘.’). You can associate a maximum of 20 file extensions with each file association.
• #11: When your app is launched to handle a particular file type, a deep link URI is used to take the user to your app. Within the URI, the FileTypeAssociation string designates that the source of the URI is a file association and the fileToken parameter contains the file token. Upon launch, map the incoming deep link URI to an app page that can handle the file. Your app will launch at the standard launch page, but if you have multiple pages to handle multiple file types, create a custom URI mapper and in it call the GetSharedFileName method to check the file type before mapping the URI.
• #12: Here’s an example of a custom URI Mapper.This first checks that the deep link Uri is from a File Type Association. It then extracts the FileID which has been supplied in the deeplink URI query string, which you can pass to the SharedStorageAccessManager.GetSharedFileName() method to get the filename of the fie you are being sent.
• #13: Then based on the file extension, we route the request to a particular page.
• #14: This is how you wire in your custom URI Mapper.When the app is launched, it assigns the URI mapper during initialization. Before launching any pages, the app calls the MapUri method of the URI mapper to determine which page to launch. The URI that the URI mapper returns is the page that the app launches.
• #15: Don’t be mistaken into thinking that the SharedStorage area is some kind of shared folder to which you have complete read/write access.No, it’s just a temporary storage area used by the OS where it stores the file while it attempts to launch your app.[Click to play animation]The file comes in either by email, or from a webpage, or from another app and is copied into SharedStorage.Your app is then launched and passed a token to that file, and all it can do is to copy that file from SharedStorage into its local folder, whereupon it can open the file and process it.
• #16: In your app, your UriMapper has mapped the File Association launch into a navigation to a particular page.On the target page, your OnNavigatedTo method executes as normal, and you can extract the data from the query string (you must be sure that your UriMapper passes the File Token in the query string it sends to the launched page).Then you can use the SharedStorageAccessManager.GetSharedFileName(fileToken) to get the name of the file, and the SharedStorageAccessManager.CopySharedFileAsync(…) method to copy the file from SharedStorage into the local folder.
• #17: As mentioned earlier, your app also can launch a file, so another app can open it. To do this, use the LauncherLaunchFileAsync(IStorageFile) method from the Launcher object of the Windows.System namespace. For example, the code shown launches a fictitious Contoso bug query file from local storage.
• #18: There are over 100 reserved file extensions, including all the usual suspects.See the docs for full details.
• #19: For demonstration notes please look in the “Demonstration” folder and open the corresponding Word document.
• #21: A URI association allows your app to automatically launch when another app launches a special URI. What makes that URI special is that it begins with a URI scheme name that your app has registered for. The URI scheme name is the portion of the URI that comes just before the colon (‘:’). The URI scheme includes the URI scheme name and all of the URI that follows the colon. For example, in the URI scheme shown, contoso is the URI scheme name.After the colon, the rest of the URI is open to however you want to use the URI association. When your app is launched, it has the opportunity to inspect the URI and behave differently based on what is in the URI. In this example, the receiving app has been designed to show all products within a particular category.
• #22: To register your app for a protocol association, add a Protocol element inside the Extensions element.Extensions - Must follow the Tokens element.FileTypeAssociation -Describes a file association. You can register a maximum of 20 file associations. The Name attribute is required, but you choose your own friendly name. Specify the TaskID and NavUriFragment elements as shown.Logos - Lists all logos for a file association. This is optional when no logos are specified. You must provide all sizes (small, medium, large) if you provide any.SupportedFileTypes - Lists all file extensions that are associated with the file type.FileType - Lists the file extension that is associated with the file type, including the period (‘.’). You can associate a maximum of 20 file extensions with each file association.
• #23: The process of handling a launch for a protocol association is exactly the same as with File associations. In this case, the deep link URI starts with /Protocol?encodedLaunchUri, so create a UriMapper that looks for that and maps the launch to the appropriate page in your application.
• #24: One app can use this to launch another app. To do this, use the LauncherUriAsync(Uri) method from the Launcher object of the Windows.System namespace.
• #25: As with file associations, certain URIs are reserved for system use. If you try to reserve one of tese, your registration request will be ignored.Again, see the docs for full details.
• #26: As already mentioned in the Accessing Phone Resources module, the LaunchUriAsync method is also used to launch several built-in applications. This usage is shown here in this table, and as you can see is mainly used for launching settings dialogs, but may also be used to launch the browser or the built-in New email application.
• #27: Certain of the built-in URIs map to the Windows Phone Store. This is useful for adding links onto the ‘About’ page of your app to encourage users to add feedback (positive hopefully!) or to lead them to other apps you have published.
• #28: For demonstration notes please look in the “Demonstration” folder and open the corresponding Word document.