BLACK FRIDAY SALE: Save 50% on all my Swift books and bundles! >>

How to support low data mode networking using allowsConstrainedNetworkAccess

Swift version: 5.6

Paul Hudson    @twostraws   

iOS lets users enable Low Data Mode for any cellular or WiFi connection, which signals to apps that they should be careful how much data they use. This might mean downloading lower-resolution images, it might mean disabling prefetching, or some other way of cutting down on bandwidth use.

By default your app does not honor the user’s low data mode setting, but you can change that by setting the allowsConstrainedNetworkAccess property to false for a given URLRequest. For example:

var request = URLRequest(url: someURL)
request.allowsConstrainedNetworkAccess = false

When that request executes iOS will immediately return an error if low data mode is enabled, which might be your cue to do another request for less data or lower-resolution images, for example. You can detect this error by typecasting it to a URLError, then checking if the networkUnavailableReason property is set to .constrained:

if let error = error as? URLError, error.networkUnavailableReason == .constrained {
    // user has activated low data mode so this request could not be satisfied

Tip: There is a similarly named URLSession property called allowsExpensiveNetworkAccess, which determines whether network requests can be made over a personal hotspot. It’s considered expensive because often users on cellular networks have lower data caps, but broadly speaking you should prefer working with low data mode because it gives users control.

Save 50% in my Black Friday sale.

SAVE 50% To celebrate Black Friday, all our books and bundles are half price, so you can take your Swift knowledge further without spending big! Get the Swift Power Pack to build your iOS career faster, get the Swift Platform Pack to builds apps for macOS, watchOS, and beyond, or get the Swift Plus Pack to learn advanced design patterns, testing skills, and more.

Save 50% on all our books and bundles!

Sponsor Hacking with Swift and reach the world's largest Swift community!

Available from iOS 13.0

Similar solutions…

About the Swift Knowledge Base

This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.

Buy Pro Swift Buy Pro SwiftUI Buy Swift Design Patterns Buy Testing Swift Buy Hacking with iOS Buy Swift Coding Challenges Buy Swift on Sundays Volume One Buy Server-Side Swift Buy Advanced iOS Volume One Buy Advanced iOS Volume Two Buy Advanced iOS Volume Three Buy Hacking with watchOS Buy Hacking with tvOS Buy Hacking with macOS Buy Dive Into SpriteKit Buy Swift in Sixty Seconds Buy Objective-C for Swift Developers Buy Beyond Code

Was this page useful? Let us know!

Average rating: 5.0/5

Unknown user

You are not logged in

Log in or create account

Link copied to your pasteboard.