今天調(diào)查了下IOS 4.0 支持的多任務(wù)的事宜，系統(tǒng)是4.2， 初步結(jié)果如下：



Ios 4.0 多任務(wù)不是傳統(tǒng)意義上的多任務(wù)。只是把程序的狀態(tài)保存起來，程序掛起。因?yàn)锳pple還沒準(zhǔn)備好多任務(wù)同時(shí)運(yùn)行，

主要是因?yàn)閎attery和memory這兩個(gè)問題還沒有解決。



現(xiàn)在IOS 4多任務(wù)支持的類型（官網(wǎng)）：

<!--[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(dāng)用戶掛起程序時(shí)，如果還有task沒完成，可以把改task完成。



但這個(gè)是有限制的，時(shí)間的限制，就是說你的后臺(tái)程序不能執(zhí)行超過某個(gè)時(shí)間。

我剛才打log看了，系統(tǒng)返回500s，既是8分鐘，8分鐘如果還沒執(zhí)行完，就會(huì)自動(dòng)把我們程序結(jié)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(jié)

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