ios后臺更新和下載

- (BOOL)application:(UIApplication )application didFinishLaunchingWithOptions:(NSDictionary )launchOptions {
    [application setMinimumBackgroundFetchInterval:UIApplicationBackgroundFetchIntervalMinimum];
    NSLog(@"Launched in background %d",UIApplicationStateBackground == application.applicationState);
    return YES;
}
// 1.利用Background Fetch


(void)application:(UIApplication )application performFetchWithCompletionHandler:(void (^)(UIBackgroundFetchResult))completionHandler {
  NSURLSessionConfiguration sessionConfiguration = [NSURLSessionConfiguration defaultSessionConfiguration];
  NSURLSession session = [NSURLSession sessionWithConfiguration:sessionConfiguration];
  NSURL url = [[NSURL alloc] initWithString:@"http://127.0.0.1/data.json"];
  NSURLSessionDataTask *task = [session  dataTaskWithURL:url
                                   completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
                                       if (error) {
                                           completionHandler(UIBackgroundFetchResultFailed);
                                           return;
                                       }
                                       completionHandler(UIBackgroundFetchResultNewData);
                                   }];

  [task resume];
}
// 2.利用Remote Notification
/
推送的內容
{
"aps" : {
"content-available" : 1
},
"content-id" : 42
}/
(void)application:(UIApplication )application
didReceiveRemoteNotification:(NSDictionary )userInfo
fetchCompletionHandler:(void (^)(UIBackgroundFetchResult))completionHandler
{
  NSLog(@"Received remote notification with userInfo %@", userInfo);
NSNumber contentID = userInfo[@"content-id"];
  NSString downloadURLString = [NSString stringWithFormat:@"http://yourserver.com/downloads/%d.mp3", [contentID intValue]];
  NSURL* downloadURL = [NSURL URLWithString:downloadURLString];
NSURLRequest request = [NSURLRequest requestWithURL:downloadURL];
  NSURLSessionDownloadTask task = [[self backgroundURLSession] downloadTaskWithRequest:request];
  task.taskDescription = [NSString stringWithFormat:@"Podcast Episode %d", [contentID intValue]];
  [task resume];
  completionHandler(UIBackgroundFetchResultNewData);
}

(NSURLSession )backgroundURLSession
{
  static NSURLSession session = nil;
  static dispatch_once_t onceToken;
  dispatch_once(&onceToken, ^{

  NSString *identifier = @"io.objc.backgroundTransferExample";
  NSURLSessionConfiguration* sessionConfig = [NSURLSessionConfiguration backgroundSessionConfiguration:identifier];
  session = [NSURLSession sessionWithConfiguration:sessionConfig
                                          delegate:self
                                     delegateQueue:[NSOperationQueue mainQueue]];

});
  return session;
}
</pre>