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）：
§ Background
audio
§ Voice
over IP
§ Background
location
§ Push
notifications
§ Local
notifications
§ Task
finishing - If your app is in mid-task when your customer leaves it,
the app can now keep running to finish the task.
§ 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];
}
}
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