Browse and download newspaper and magazine assets in the background.
- iOS 5.0+
You use the Newsstand Kit framework to develop the client side of a Newsstand application. Through the Newsstand, users can browse through newspapers and magazines that are optimized for viewing on mobile devices.
The Newsstand Kit framework has three classes:
NKLibrary—Represents the application’s library of newsstand issues.
NKIssue—Represents a publication’s issue in the library.
NKAsset—Represents an asset that is downloaded (or that has downloaded) from the application’s server.
An asset can be a component of the online issue such as an HTML or image file. It can also be a compressed archive (such as a ZIP file) that, once uncompressed, contains all the components of an issue in a ready-to-display form.
In addition, the framework adds a property (via a category) to the
NSURLConnection class. This property associates a URL connection with a downloading (or downloaded) asset.
A newsstand content application is capable of running in the background to start downloads or process delegate events related to issue assets. To request this capability, specify
newsstand-content as the string value of one of the array elements of the
UIBackground property in the application’s
Info file. This property also enables applications to be launched in the background via push notifications.
The following steps describe the general workflow for getting newsstand content when push notifications trigger the download. If push notifications are not involved, skip the first step:
The server side of the application sends a push notification to client applications when there is a new issue to download.
If an application is not running in the foreground when the notification is delivered, it is activated in the background (or launched into the background, if necessary) to download issue assets. Otherwise, you handle the notification as you would any push notification. See Local and Remote Notification Programming Guide for information on how to send and handle push notifications.
The client application communicates with its server and gets URLs locating the issue assets to download. It might also need to obtain the name and date of the issue from the server. In this phase it might also validate that the user is eligible for a subscription or perform any other required authorization.
The client gets the shared
NKLibraryinstance and sends a
addmessage to it, passing in the issue name and date. This step creates an
Issue(with Name: date:)
NKIssueobject representing the issue and adds it to the library.
With each URL locating a downloadable asset on the application’s server, the client creates an
The delegate monitors the downloading of the asset and updates a progress indicator. When downloading is finished, it processes the downloaded asset.
Processing might involve uncompressing an archive or other actions before moving the asset to the assigned location of the issue in the application sandbox.
While assets are being downloaded, the application could be suspended or even terminated entirely if, for instance, there is insufficient memory or the user force-quits the application. The application (assuming it has the
newsstand-content property) is later relaunched into the background to handle the completion of the download or any authentication challenges or errors related to it. The procedure in this case is the following:
When the application is launched, it can use the
newsstandkey to access an array in the
launchdictionary passed into the
application(_:. If there is an array, it contains the identifiers that caused the launch; these could be identifiers for downloads that have finished downloading or that could not complete downloading.
did Finish Launching With Options:)
It iterates through the array of
NKAssetobjects from the
downloadingproperty of the
NKLibraryobject and calls
download(with:)on each of them. If it wants, the application can use the asset identifiers obtained in the previous step to check which asset downloads caused the relaunch.
NSURLConnectionobject handles the asset downloads as it does normally.
The Newsstand Kit framework expects all calls of its methods to be made on the main thread; the
NSURLConnection methods are also invoked on the main thread.