As I have promised three weeks ago (and again a few days ago) I finally got around to writing this little how-to.
I’m sorry for the delay. I hope this helps someone, anyway.

Mind you, this is my first attempt at writing a how-to, and most of it was done, while I was being tired. Also, English isn’t my native language, so please excuse any typos or other errors, you may find.

If you have any suggestions, how to improve this, please feel free to leave a comment.

Now, have fun!

Preface

We will create an iPhone application, that keeps the iPhone from deep sleeping, while it’s running. It’s not a really useful application, as it does nothing but just that, but you can easily adapt the stuff you learn here and use it for your own application(s).

Here’s exactly what we’re going to do:
We will …

• … create a new project in Xcode.
• … add the necessary frameworks to this project.
• … add a silent sound file to this project.
• … create a class called “DeepSleepPreventer” and add it to this project.
• … then use this class to prevent the iPhone from deep sleeping.

You can use this class in your other apps, to prevent them from sleeping. Just add the needed frameworks and the DeepSleepPreventer class to your app and use the DeepSleepPreventer, whenever you need it.

Create a New Project in Xcode

I’m sure you all know, how to do this, but for completeness’ sake, I’ll just go through the whole process, step by step.

Fire up Xcode. Click “File” -> “New Project”. We are gonna use the “View-based Application” template for this how-to, so select it and click “Choose…”.

Choose a location and name under which you want to save the project and click on “Save”. I’m going to use “iPhoneInsomnia” as a name and save the project to my desktop (I know, I have a lot to tidy, judging by the screenshot).

Add the Necessary Frameworks

Now we’ll add the AVFoundation and the AudioToolbox frameworks to our project, as we will need them later on.

In your project window, right-click (or control-click) your “Frameworks” group in the “Groups & Files” pane and click on “Add” -> “Existing Fameworks…”.

A file selection window should pop up now and it should show you the content of the current iPhone SDK’s “Library” subfolder. If your starting up somewhere else, navigate to “/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS3.0.sdk/System/Library” first (see screenshot).

Further go to the Frameworks folder and select “AudioToolbox.framework” and “AVFoundation.framework”. Then click on “Add”.

In the upcoming window uncheck the “Copy …” checkbox, if it is selected and choose “Relative to Current SDK” as reference type. Then click “Add”.

Add a Silent Sound File

Now we need to add a silent sound file. You can create it with a sound tool of your choice. I named it “noSound.wav”. You can just use the file I created, if you like. It is part of the Github repository I created for this whole project. iPhoneInsomnia @ Github

We will first create a new group, named “DeepSleepPreventer” in the “Groups & Files” pane. Because we are very tidy people, we will add the sound file and our later created custom class to this group, too.

Right-click on “iPhoneInsomnia” and click on “Add” -> “New Group” and name it “DeepSleepPreventer”.

Now right-click this group and click “Add” -> “Existing Files…” and add the sound file to the project.

Navigate to the location of your sound file, select it and click “Add”.

Check the “Copy items …” checkbox and set “Reference Type” to “Default”. Click Add.

Create our New Class

Now it’s time to finally write some code. Almost. First we need to add a new class to the project.

Right-click the “DeepSleepPreventer” group and click “Add” -> “New File…”.

Choose the “Objective-C class” template under “iPhone OS” -> “Cocoa Touch Class” and select “NSObject” on the “Subclass of” pull down. Click “Next”.

Name the file “DeepSleepPreventer.m”, Check the “Also create .h” checkbox and click “Finish”.

Now modify “DeepSleepPreventer.h” to look like this:

#import <Foundation/Foundation.h>

@class AVAudioPlayer;

@interface DeepSleepPreventer : NSObject {
	AVAudioPlayer *audioPlayer;
	NSTimer *preventSleepTimer;
}
@property (nonatomic, retain) AVAudioPlayer *audioPlayer;
@property (nonatomic, retain) NSTimer *preventSleepTimer;
- (void)playPreventSleepSound;
- (void)startPreventSleep;
- (void)stopPreventSleep;
@end

We declared two properties here: an AVAudioPlayer here, that will play our silent sound file and an NSTimer that will call -playPreventSleepSound. We actually create this timer in -startPreventSleep and invalidate it in -stopPreventSleep later.

Now we edit “DeepSleepPreventer.m” step by step.

First we import some header files, synthesize our accessors and mutators (or getters and setters, if you prefer to call them that):

#import "DeepSleepPreventer.h"
#import <AVFoundation/AVFoundation.h>
#import <AudioToolbox/AudioToolbox.h>

@implementation DeepSleepPreventer

@synthesize audioPlayer;
@synthesize preventSleepTimer;

Modify -init to set up all the stuff we need to:

- (id)init
{
    if ((self = [super init])) {
		// Activate audio session
		AudioSessionSetActive(true);
		// Set up audio session, to prevent iPhone from deep sleeping, while playing sounds
		UInt32 sessionCategory = kAudioSessionCategory_MediaPlayback;
		AudioSessionSetProperty (
			kAudioSessionProperty_AudioCategory,
			sizeof (sessionCategory),
			&sessionCategory
		);

		// Set up sound file
		NSString *soundFilePath = [[NSBundle mainBundle] pathForResource:@"noSound"
																  ofType:@"wav"];
		NSURL *fileURL = [[NSURL alloc] initFileURLWithPath:soundFilePath];

		// Set up audio player with sound file
		self.audioPlayer = [[AVAudioPlayer alloc] initWithContentsOfURL:fileURL error:nil];
		[self.audioPlayer prepareToPlay];

		// You may want to set this to 0.0 even if your sound file is silent.
		// I don't know exactly, if this affects battery life, but it can't hurt.
		[self.audioPlayer setVolume:0.0];
	}
    return self;
}

Now we implement -playPreventSleepSound:

- (void)playPreventSleepSound {
	[self.audioPlayer play];
}

This should be self explanatory.

Now -startPreventSleep (this is the method we will call, if we want the iPhone to stay awake):

- (void)startPreventSleep {
	// We need to play a sound at least every 10 seconds to keep the iPhone awake.
	// We create a new repeating timer, that begins firing now and then every ten seconds.
	// Every time it fires, it calls -playPreventSleepSound
	self.preventSleepTimer = [[NSTimer alloc] initWithFireDate:[NSDate dateWithTimeIntervalSinceNow:0]
												  interval:10.0
												target:self
												  selector:@selector(playPreventSleepSound)
												  userInfo:nil
												   repeats:YES];
	// We add this timer to the current run loop
	NSRunLoop *runLoop = [NSRunLoop currentRunLoop];
	[runLoop addTimer:self.preventSleepTimer forMode:NSDefaultRunLoopMode];
}

-stopPreventSleep stops the sleep preventing.

- (void)stopPreventSleep {
	[self.preventSleepTimer invalidate];
	self.preventSleepTimer = nil;
}

Finally -dealloc to clean up our mess:

- (void)dealloc {
	// memory management
	[preventSleepTimer release];
	[audioPlayer release];
	[super dealloc];
}
// Don't forget the matching @end to our @implementation
@end

Use the DeepSleepPreventer Class

Now switch to “iPhoneInsomniaAppDelegate.h”. We will add a property if the type or our class DeepSleepPreventer to the application delegate now. Modify “iPhoneInsomniaAppDelegate.h”, to look like this:

#import <UIKit/UIKit.h>

@class iPhoneInsomniaViewController;
@class DeepSleepPreventer;

@interface iPhoneInsomniaAppDelegate : NSObject  {
    UIWindow *window;
    iPhoneInsomniaViewController *viewController;
    DeepSleepPreventer *deepSleepPreventer;
}
@property (nonatomic, retain) IBOutlet UIWindow *window;
@property (nonatomic, retain) IBOutlet iPhoneInsomniaViewController *viewController;
@property (nonatomic, retain) DeepSleepPreventer *deepSleepPreventer;

@end

Now move on to “iPhoneInsomniaAppDelegate.m”. We will instantiate and use our DeepSleepPreventer class in -applicationDidFinishLaunching:. In your own app, you would do this in a place, where it fits best.

First we need to import our class header file and synthesize our new property:

#import "iPhoneInsomniaAppDelegate.h"
#import "iPhoneInsomniaViewController.h"
#import "DeepSleepPreventer.h"

@implementation iPhoneInsomniaAppDelegate

@synthesize window;
@synthesize viewController;
@synthesize deepSleepPreventer;

Now modify -applicationDidFinishLaunching: to look like this:

- (void)applicationDidFinishLaunching:(UIApplication *)application {
	// Here we create our deepSleepPreventer and get it to keep our iPhone from deep sleeping
	self.deepSleepPreventer = [[DeepSleepPreventer alloc] init];
	[self.deepSleepPreventer startPreventSleep];

    [window addSubview:viewController.view];
    [window makeKeyAndVisible];
}

And finally the rest of “iPhoneInsomniaAppDelegate.m”. Release our property in -dealloc:

- (void)dealloc {
    [deepSleepPreventer release];
    [viewController release];
    [window release];
    [super dealloc];
}

// Don't forget the matching @end to our @implementation
@end

Well, that’s it! We are done! :)

Use This in Your Own App

Just add the two frameworks “AVFoundation.framework” and “AudioToolbox.framework” to your own app, add the sound file “noSound.wav” and the files “DeepSleepPreventer.h” and “DeepSleepPreventer.m” to it and instantiate and use an object of the “DeepSleepPreventer” class where it fits best, and you’re ready to go.

Issues and Epilog

I couldn’t start my MPMusicPlayer in my music alarm clock app, while I was playing the silent sound with the AVAudioPlayer. So I’m guessing, it’s not possible to play other sounds while this sound plays, at least not via the MPMediaPlayer class.

As I didn’t use any other sounds in my applications yet, I don’t know if this assumption is correct. If you have any more experience with this or any more other useful or relevant information, please leave a comment. I will then update this how-to.

Also, as Shabbir Vijapura pointed out in a comment to my previous post there might be an easier way, to run timers on the iPhone, while it is asleep. I haven’t tested this myself, yet, though, so I cannot guarantee, that this really works. I will test it in the the next couple of days and then update this post, if I find the time.
Update: Appearantly this method, doesn’t work, as Shabbir pointed out in the comments.

Furthermore, if you have any experience yourself, dealing with the iPhone’s deep sleep behaviour and would like to share, or if you have any other suggestions or questions, please feel free to leave a comment.

Thanks for reading. I hope this is useful to someone out there.

Downloads

You can download this project, including all source code and the silent sound file. Feel free, to use it in your own apps.

iPhoneInsomnia @ Github

• Previous Entry: Timers and Locked Screen/Sleep Issues