allowsExpensiveNetworkAccess
A Boolean value that indicates whether connections may use a network interface that the system considers expensive.
Declaration
var allowsExpensiveNetworkAccess: Bool { get set }Discussion
The system determines what constitutes “expensive” based on the nature of the network interface and other factors. iOS 13 considers most cellular networks and personal hotspots expensive. If there are no nonexpensive network interfaces available and the session’s allowsExpensiveNetworkAccess property is false, any task created from the session fails. In this case, the error provided when the task fails has a networkUnavailableReason property whose value is NSURLErrorNetworkUnavailableReasonExpensive.
You can limit your app’s of use of expensive network access to user-initiated tasks, and put off discretionary tasks until a nonexpensive interface becomes available. To do this, set allowsExpensiveNetworkAccess (and allowsConstrainedNetworkAccess) to false and waitsForConnectivity to true. This way, your URLSessionTask waits for a suitable interface to become available before sending or receiving data.
To test the behavior of this property, you can override the device’s current values for cellular and Wi-Fi cost in Settings > Developer > Network Override.