远程推送和后台数据获取

详情：https://www.objc.io/issues/5-ios7/multitasking/

Background Fetch

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    [application setMinimumBackgroundFetchInterval:UIApplicationBackgroundFetchIntervalMinimum];

    return YES;
}

- (void)application:(UIApplication *)application performFetchWithCompletionHandler:(void (^)(UIBackgroundFetchResult))completionHandler
{
    NSURLSessionConfiguration *sessionConfiguration = [NSURLSessionConfiguration defaultSessionConfiguration];
    NSURLSession *session = [NSURLSession sessionWithConfiguration:sessionConfiguration];

    NSURL *url = [[NSURL alloc] initWithString:@"http://yourserver.com/data.json"];
    NSURLSessionDataTask *task = [session dataTaskWithURL:url 
                                        completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {

        if (error) {
            completionHandler(UIBackgroundFetchResultFailed);
            return;
        }

        // Parse response/data and determine whether new content was available
        BOOL hasNewData = ...
        if (hasNewData) {
            completionHandler(UIBackgroundFetchResultNewData);
        } else {
            completionHandler(UIBackgroundFetchResultNoData);
        }
    }];

    // Start the task
    [task resume];
}

远程推送

推送内容结构

{
    "aps" : {
        "content-available" : 1
    },
    "content-id" : 42
}

实现

SELECT ALL
- (void)application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)userInfo fetchCompletionHandler:(void (^)(UIBackgroundFetchResult))completionHandler
{
    NSLog(@"Remote Notification userInfo is %@", userInfo);

    NSNumber *contentID = userInfo[@"content-id"];
    // Do something with the content ID
    completionHandler(UIBackgroundFetchResultNewData);
}

后台网络请求

- (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;
}

- (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);
}

当网络请求完成的时候，如果app还处于后台状态，需要实现下面代码

- (void)application:(UIApplication *)application 
  handleEventsForBackgroundURLSession:(NSString *)identifier completionHandler:(void (^)())completionHandler
{
    // You must re-establish a reference to the background session, 
    // or NSURLSessionDownloadDelegate and NSURLSessionDelegate methods will not be called
    // as no delegate is attached to the session. See backgroundURLSession above.
    NSURLSession *backgroundSession = [self backgroundURLSession];

    NSLog(@"Rejoining session with identifier %@ %@", identifier, backgroundSession);

    // Store the completion handler to update your UI after processing session events
    [self addCompletionHandler:completionHandler forSession:identifier];
}

- (void)URLSessionDidFinishEventsForBackgroundURLSession:(NSURLSession *)session
{
    NSLog(@"Background URL session %@ finished events.\n", session);

    if (session.configuration.identifier) {
        // Call the handler we stored in -application:handleEventsForBackgroundURLSession:
        [self callCompletionHandlerForSession:session.configuration.identifier];
    }
}

- (void)addCompletionHandler:(CompletionHandlerType)handler forSession:(NSString *)identifier
{
    if ([self.completionHandlerDictionary objectForKey:identifier]) {
        NSLog(@"Error: Got multiple handlers for a single session identifier.  This should not happen.\n");
    }

    [self.completionHandlerDictionary setObject:handler forKey:identifier];
}

- (void)callCompletionHandlerForSession: (NSString *)identifier
{
    CompletionHandlerType handler = [self.completionHandlerDictionary objectForKey: identifier];

    if (handler) {
        [self.completionHandlerDictionary removeObjectForKey: identifier];
        NSLog(@"Calling completion handler for session %@", identifier);

        handler();
    }
}