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How to detect low power mode is enabled

Swift version: 5.1

Paul Hudson    @twostraws   

When a user has enabled low-power mode you probably want to avoid doing CPU-intensive work: not only is the system less able to give you resources, but you always want to respect the user's wishes and help their battery last as long as possible.

There are two ways of checking for low-power mode: you can read a property whenever you need it, or register for a notification. First, here's an example with the property:

func doComplicatedWork() {
    guard ProcessInfo.processInfo.isLowPowerModeEnabled == false else { return }

    // continue doing complicated work here
}

You can also register to be notified when the lower power mode state changes, like this:

NotificationCenter.default.addObserver(self, selector: #selector(powerStateChanged), name: Notification.Name.NSProcessInfoPowerStateDidChange, object: nil)

When that method is triggered, you can check the new value of isLowPowerModeEnabled to see what state the device is in:

@objc func powerStateChanged(_ notification: Notification) {
    let lowerPowerEnabled = ProcessInfo.processInfo.isLowPowerModeEnabled
    // take appropriate action
}

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Available from iOS 9.0

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