iOS: Keep application running in background

Question

How do I keep my application running in the background? Would I have to jailbreak my iPhone to do this? I just need this app to check something from the internet every set interval and notify when needed, for my own use.

Helluva

Hi Denis hope you have got your answer. If yes, then can you please mark your respective answer as true and up vote as well... – Cyanogen

Answer 1

Yes, no need to jailbreak. Check out the "Implementing long-running background tasks" section of this doc from Apple.

From Apple's doc: Declaring Your App’s Supported Background Tasks

Support for some types of background execution must be declared in advance by the app that uses them. An app declares support for a service using its Info.plist file. Add the UIBackgroundModes key to your Info.plist file and set its value to an array containing one or more of the following strings: (see Apple's doc from link mentioned above.)

Parodist

@takrishna, If you are writing this app for your own use, then set UIBackgroundModes value "voip" (Voice over IP). That is the easiest type of app to keep alive forever in background. (But don't submit it to app store, unless it really is a VOIP app.) – Ernestinaernestine

For an app store app, if you don't have a server to periodically send "Remote notifications" to your phone, your only other option is "Background fetch". https://mcmap.net/q/539150/-repeating-a-task-when-app-is-in-background-e-g-pull-something-from-a-server-without-apns – Ernestinaernestine

Answer 2

I guess this is what you required

When an iOS application goes to the background, are lengthy tasks paused?

iOS Application Background Downloading

This might help you ...

Enjoy Coding :)

Cyanogen

Answer 3

I found a way, to keep app running in background by playing silence

Make sure, that you selected audio playback in background modes

Also, don't use this method for long time, since it consumes CPU resources and battery juice, but I think it's a suitable way to keep app alive for a few minutes.

Just create an instance of SilencePlayer, call play() and then stop(), when you done

import CoreAudio

public class SilencePlayer {
    private var audioQueue: AudioQueueRef? = nil
    public private(set) var isStarted = false

    public func play() {
        if isStarted { return }
        print("Playing silence")
        let avs = AVAudioSession.sharedInstance()
        try! avs.setCategory(AVAudioSessionCategoryPlayback, with: .mixWithOthers)
        try! avs.setActive(true)
        isStarted = true
        var streamFormat = AudioStreamBasicDescription(
            mSampleRate: 16000,
            mFormatID: kAudioFormatLinearPCM,
            mFormatFlags: kLinearPCMFormatFlagIsSignedInteger | kLinearPCMFormatFlagIsPacked,
            mBytesPerPacket: 2,
            mFramesPerPacket: 1,
            mBytesPerFrame: 2,
            mChannelsPerFrame: 1,
            mBitsPerChannel: 16,
            mReserved: 0
        )
        let status = AudioQueueNewOutput(
            &streamFormat,
            SilenceQueueOutputCallback,
            nil, nil, nil, 0,
            &audioQueue
        )
        print("OSStatus for silence \(status)")
        var buffers = Array<AudioQueueBufferRef?>.init(repeating: nil, count: 3)
        for i in 0..<3 {
            buffers[i]?.pointee.mAudioDataByteSize = 320
            AudioQueueAllocateBuffer(audioQueue!, 320, &(buffers[i]))
            SilenceQueueOutputCallback(nil, audioQueue!, buffers[i]!)
        }
        let startStatus = AudioQueueStart(audioQueue!, nil)
        print("Start status for silence \(startStatus)")
    }

    public func stop() {
        guard isStarted else { return }
        print("Called stop silence")
        if let aq = audioQueue {
            AudioQueueStop(aq, true)
            audioQueue = nil
        }
        try! AVAudioSession.sharedInstance().setActive(false)
        isStarted = false
    }

}

fileprivate func SilenceQueueOutputCallback(_ userData: UnsafeMutableRawPointer?, _ audioQueueRef: AudioQueueRef, _ bufferRef: AudioQueueBufferRef) -> Void {
    let pointer = bufferRef.pointee.mAudioData
    let length = bufferRef.pointee.mAudioDataByteSize
    memset(pointer, 0, Int(length))
    if AudioQueueEnqueueBuffer(audioQueueRef, bufferRef, 0, nil) != 0 {
        AudioQueueFreeBuffer(audioQueueRef, bufferRef)
    }
}

Tested on iOS 10 and Swift 4

Amathiste

Thank you for sharing this. – Attentive

:- How much time silence player plays sound? – Attentive

@YogeshRaut it plays silence until you call stop() – Amathiste

@DimaRostopira I'm doing something similar to this but notice my app still gets quit after a few hours. My code does use AVAudioPlayer mind rather than audio queues like yours, how long have you seen this successfully keep your app running for? – Practicable

@Practicable I'm using this only for 3 minutes, I don't need more than that – Amathiste

@DimaRostopira okay fair enough! :) – Practicable

@DimaRostopira Why did you use so complex code? All examples with silent sound I saw before was contains AVAudioPlayer (numberOfLoops = -1). Is there some kind of trick? – Bordy

@Bordy I already had code, that was used to play raw audio using audio queues, so I just adapted it to play silence. No tricks here – Amathiste

@DimaRostopira Did you compare AVAudioPlayer vs audio queues in background? Is there any pros/cons between them? I don't know which one to choose. I've tested AVAudioPlayer (empty sound, infinity loops) and sometimes I had LocalPlayerHandleCallback crashes. Maybe you know much more than I do. I appreciate your help, thank you. – Bordy

@Bordy never compared, and I have no idea, sorry – Amathiste

Answer 4

Use local notifications to do that. But this will not check every time. You will have to set a time where you will check your specific event, you may shorten this by decreasing your time slot. Read more about local notification to know how to achieve this at:

http://developer.apple.com/library/mac/#documentation/NetworkingInternet/Conceptual/RemoteNotificationsPG/Introduction/Introduction.html

Sherysherye

No, if the app is in background, all that a local notification will do is show that notification to the user. You can't do any actual work unless the user clicks on the notification to bring the app to foreground. – Ernestinaernestine

Answer 5

I know this is not the answer to your question, but I think it is a solution.

This assumes that your trying to check something or get data from the internet on a regular basis?

Create a service that checks the internet every set interval for whatever it is you want to know, and create a push notification to alert you of it, if the server is down, or whatever it is your trying to monitor has changed state. Just an idea.

Vertex

Answer 6

Yes you can do something like this. For that you need to set entry in info.plist to tell os that my app will run in background. I have done this while I wanted to pass user's location after particular time stamp to server. For that I have set "Required background modes" set to "App registers for location updates".

You can write a handler of type UIBackgroundTaskIdentifier.

Conley

Answer 7

You can already do this in the applicationDidEnterBackground Method

Molality

I thought the app will automatically be terminated after some duration, will it not? Pardon my ignorance if I'm wrong. I'm very new to iOS programming. – Helluva

unless iOS needs that memory for another app, it won't be, and as long as you are doing something in the background – Molality

No. Applications cannot run in the background for over 10 minutes, except for a few certain situations (VOIP, playing audio, etc.) – Detour

An iOS app which plays audio will keep playing audio indefinitely in the background so long as the audio is playing. If the app then stops or pauses the audio it will be terminated after 10 minutes. I know this because I have a sleep timer in an app. The code above seems to have a lot of lines so I'm guessing it's capable of being simplified. I have audio playing in background with much less code. – Noontime