今天調查了下IOS 4.0 支持的多任務的事宜，系統是4.2， 初步結果如下：



Ios 4.0 多任務不是傳統意義上的多任務。只是把程序的狀態保存起來，程序掛起。因為Apple還沒準備好多任務同時運行，

主要是因為battery和memory這兩個問題還沒有解決。



現在IOS 4多任務支持的類型（官網）：

<!--[if !supportLists]-->§ <!--[endif]-->Background audio

<!--[if !supportLists]-->§ <!--[endif]-->Voice over IP

<!--[if !supportLists]-->§ <!--[endif]-->Background location

<!--[if !supportLists]-->§ <!--[endif]-->Push notifications

<!--[if !supportLists]-->§ <!--[endif]-->Local notifications

<!--[if !supportLists]-->§ <!--[endif]-->Task finishing - If your app is in mid-task when your customer leaves it, the app can now keep running to finish the task.

<!--[if !supportLists]-->§ <!--[endif]-->Fast app switching - All developers should take advantage of fast app switching, which allows users to leave your app and come right back to where they were when they left - no more having to reload the app.



我使用的是Task finishing， 既當用戶掛起程序時，如果還有task沒完成，可以把改task完成。



但這個是有限制的，時間的限制，就是說你的后臺程序不能執行超過某個時間。

我剛才打log看了，系統返回500s，既是8分鐘，8分鐘如果還沒執行完，就會自動把我們程序結束。



代碼如下 #pragma mark -

#pragma mark Background Task Handle

- (void)applicationDidEnterBackground:(UIApplication *)application {


// Request permission to run in the background. Provide an

// expiration handler in case the task runs long.

NSAssert(self->bgTask == UIBackgroundTaskInvalid, nil);

self->bgTask = [application beginBackgroundTaskWithExpirationHandler: ^{

// Synchronize the cleanup call on the main thread in case

// the task catully finished at around the same time.

dispatch_async(dispatch_get_main_queue(), ^{

if (UIBackgroundTaskInvalid != self->bgTask) {

[application endBackgroundTask:self->bgTask];

self->bgTask = UIBackgroundTaskInvalid;

}

});

}];

// Start the long-running task and return immediately.

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0),

^{

// Do the work assoicated with the task.

for(int i = 0; i < 1000; i++) {

//request network.

NSLog(@"hahah %d, Time Remain = %f", i, [application backgroundTimeRemaining]);

}

// Synchronize the cleanup all on the main thread in case

// the task catully finished at around the same time.

dispatch_async(dispatch_get_main_queue(), ^{


if (UIBackgroundTaskInvalid != self->bgTask) {


[application endBackgroundTask:self->bgTask];

self->bgTask = UIBackgroundTaskInvalid;

}

});

});

}

#pragma mark -

#pragma mark Local Notifications

- (void)scheduleAlarmForDate:(NSDate *)theDate {

UIApplication *app = [UIApplication sharedApplication];

NSArray *oldNotifications = [app scheduledLocalNotifications];

// Clear out the old notification before scheduling a new one.

if (0 < [oldNotifications count]) {

[app cancelAllLocalNotifications];

}

// Create a new notification

UILocalNotification *alarm = [[UILocalNotification alloc] init];

if (alarm) {


alarm.fireDate = theDate;

alarm.timeZone = [NSTimeZone defaultTimeZone];

alarm.repeatInterval = 0;

alarm.soundName = @"ping.caf";//@"default";

alarm.alertBody = [NSString stringWithFormat:@"Time to wake up!Now is\n[%@]",

[NSDate dateWithTimeIntervalSinceNow:10]];

[app scheduleLocalNotification:alarm];

[alarm release];

}

}

總結

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