How to support low data mode in iOS 13? - ios

Question

"Low Data Mode" is introduced in iOS 13. See "Settings" section Apple's iOS 13 overview:
I couldn't find any developer documentation on this.
Is this something third party app developers can opt into, as suggested by MacRumors? Or is will it just suspend background activity when not connected to Wi-Fi, as suggested by AppleInsider?

Answer 1

To determine if iOS is currently in Low Data mode, you can use the Network library:
import Network // Put this on top of your class
let monitor = NWPathMonitor()
monitor.pathUpdateHandler = { path in
if path.isConstrained {
// Path uses an interface in Low Data Mode.
}
else if path.isExpensive {
// Path uses an interface that is considered expensive, such as Cellular or a Personal Hotspot.
}
}
monitor.start(queue: DispatchQueue.global(qos: .background))

Answer 2

URLSession supports LowData mode in iOS 13.
Steps
Provide two different resources for high resolution and low resolution(low data mode)
If statusCode == 200 (low data mode is disabled in setting).
If error.networkAvailableReason == .constrained (low data mode is enable in settings)
Check out Advances in Networking, Part 1 from WWDC 2019 from 16:00 for a demo and sample code. You can use Combine to make the code simpler, but this is not required.

Answer 3

First of all, you need to configure your URLSession (NSURLSession) to either allow or disallow expensive or constrained network connections to be opened.
You can do that by changing URLSession's respective properties allowsExpensiveNetworkAccess or allowsConstrainedNetworkAccess to false (NO).
If a URLSessionTask results in an error that is either an NSURLErrorNotConnectedToInternet error containing NSURLErrorNetworkUnavailableReasonKey entry in userInfo (Objective-C) or an URLError with a non-nil NetworkUnavailableReason property set (Swift), then you need to act accordingly.
Those reasons can be:
expensive
constrained
cellular
The cellular reason has sort of been there since iOS 7, so it's not new, but the entire reason enumeration is, as Apple streamlined connection type handling a bit this year.

Answer 4

Here is the solution in Xamarin, for those interested:
NWPathMonitor monitor = new NWPathMonitor();
monitor.SetUpdatedSnapshotHandler(path =>
{
if (path.Status == NWPathStatus.Satisfied)
{
if(path.IsConstrained)
{
// Path uses an interface in Low Data Mode.
}
}
});
monitor.SetQueue(CoreFoundation.DispatchQueue.DefaultGlobalQueue);
monitor.Start();