iOS 4闹钟应用程序，支持多任务处理

Question

I'm making an alarm clock app with multitasking support. However, I'm stuck with some limitations of the sdk.

I need to play selected alarm sound whenever the alarm time comes with some properties set by the user. These properties: - Alarm sound can be a music from the user's iPod library, and also some sound files in application bundle. - Alarm sound can be set to play as progressive.

Moreover, alarm sound must be played in background in a loop until the user cancels or wakes the app.

First logical thing that came to my mind was to use local notifications, but with local notifications you can play sound files that are only in app bundle(not iPod music) and that are at most 30 seconds long. Also you are not get notified when the user cancels the notification alert, iOS just stops playing your sound.

Now I'm thinking of using background audio playing option and play silence until the alarm time, and then play the alarm sound while also showing a local notification without sound. But again how will I know if user cancelled the local notification alert and stop playing audio. However according to Apple's documentation iPod music playing(and use of shared resources) is still not allowed for an app that is playing background audio.

I also can't understand how some other apps are doing some of these features. For example, Night Stand HD can play iPod music while in the background, and an app named "Progressive Alarm Clock" can play progressive sound while in the background.

Any ideas and suggestions on these issues? Any of your help will be greatly appreciated

Answer 1

I would say what you want to do is not possible with the current restrictions of iOS. That said you can probably fake a progressive alarm by doing what the developer of Progressive Alarm Clock do to play the progressive alarm. By scheduling many local notifications, one after each other. He has divided the alarm sounds into chunks of say 10 s each with progressive volume levels. This is a very crude example to show how the progressive alarm can be faked.

UILocalNotification *notif1 = [[UILocalNotification alloc] init];
notif1.fireDate = [NSDate dateWithTimeIntervalSinceNow:15];
notif1.soundName = UILocalNotificationDefaultSoundName;
notif1.alertBody = @"Alarm";
[[UIApplication sharedApplication] scheduleLocalNotification:notif1];
[notif1 release];

UILocalNotification *notif2 = [[UILocalNotification alloc] init];
notif2.fireDate = [NSDate dateWithTimeIntervalSinceNow:20];
notif2.soundName = UILocalNotificationDefaultSoundName;
[[UIApplication sharedApplication] scheduleLocalNotification:notif2];
[notif2 release];

This will first display a notification and play the default sound after 15 seconds. After 5 seconds more the sound will be played again. By having a bunch of sound files where the volume is increasing the progressive sound can be faked just by scheduling more local notifications. This will of course only work if you have an alarm sound that can be easily divided into chunks, just like the bells in Progressive Alarm Clock. Unfortunately you can't cancel the alarm by tapping cancel in the notification. You have to start the application to do that.

Answer 2

Whatever the Progressive Alarm Clock developer is doing, it's not what Robert Höglund is describing, AFAIK, since the alarm will sound even if the phone is in silent, and UILocalNotification doesn't seem to have any way to allow for this. In addition, if you kill the app manually while an alarm is pending, the app will notify you that it needs to relaunch. This seems to suggest that it must be somehow running in the background.