Today widget Content update life cycle

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.

widgetPerformUpdate :
called when widget is updated in background.
called before widget snapshot is taken.

func widgetPerformUpdate(completionHandler: @escaping (NCUpdateResult) -> Swift.Void)
    {
        completionHandler(.newData)
    }

references:
https://hackernoon.com/app-extensions-and-today-extensions-widget-in-ios-10-e2d9fd9957a8