iOs Widget background update
The widget life-cycle is managed by the iOS itself.
When you go to background, the system takes a snapshot of your today's widget. The system manages the background fetch (background life cycle of your widget), it'll call the widgetPerfomrUpdateWithComplationHandler: for updating your widget data whenever possible and takes a snapshot each time. And when you open it again, it'll load the most recent snapshot first and loads the live data after that.
Widget Content Update
Updating Content
The Today extension point provides API for managing a widget’s state and handling updates to its content (you can read about this API in the Notification Center Framework Reference). Although there are a few platform-specific differences in the Today API, the functionality supported on both platforms is mostly the same.
To help your widget look up to date, the system occasionally captures snapshots of your widget’s view. When the widget becomes visible again, the most recent snapshot is displayed until the system replaces it with a live version of the view.
To update a widget’s state before a snapshot is taken, be sure to conform to the NCWidgetProviding protocol. When your widget receives the widgetPerformUpdateWithCompletionHandler: call, update your widget’s view with the most recent content and call the completion handler, using one of the following constants to describe the result of the update:
NCUpdateResultNewData—The new content required you to redraw the view
NCUpdateResultNoData—The widget doesn’t require updating
NCUpdateResultFailed—An error occurred during the update process
Reference Today Widget
Notification Center Data Updating
Notification Center
Note
The schedule and intended use of widgetPerformUpdateWithCompletionHandler: is intended as a convenient home for all data/model update logic. If implemented, the system will call at opportune times for the widget to update its state, both when Notification Center is visible, as well as in the background. An implementation is required to enable background updates. It’s expected that the widget will perform the work to update asynchronously and off the main thread as much as possible. Widgets should call the argument block when the work is complete, passing the appropriate NCUpdateResult. Widgets should NOT block returning from viewWillAppear: on the results of this operation. Instead, widgets should load cached state in viewWillAppear: in order to match the state of the view from the last viewWillDisappear:, then transition smoothly to the new data when it arrives.
Reference iOS 8.1 Notification Center
Widget Life Cycle
Reference: An App Extension’s Life Cycle
iOS8 release notes
Note The schedule and intended use of widgetPerformUpdateWithCompletionHandler: is intended as a convenient home for all data/model update logic. If implemented, the system will call at opportune times for the widget to update its state, both when Notification Center is visible, as well as in the background. An implementation is required to enable background updates. It’s expected that the widget will perform the work to update asynchronously and off the main thread as much as possible. Widgets should call the argument block when the work is complete, passing the appropriate NCUpdateResult. Widgets should NOT block returning from viewWillAppear: on the results of this operation. Instead, widgets should load cached state in viewWillAppear: in order to match the state of the view from the last viewWillDisappear:, then transition smoothly to the new data when it arrives.
You need to implement both
- viewDidAppear:
- widgetPerformUpdateWithComplationHandler:
Refresh your data in widgetPerformUpdateWithComplationHandler: then call the completion block with NCUpdateResult.
Refresh your view in viewDidAppear: The launch image (snapshot) will be from your last viewDidDissappear: New contents will be displayed at the end of the next run loop.
Credit to DigitalBrain_Dev for document reference.