变更记录

序号 录入时间 录入人 备注
1 2015-03-03 Alfred Jiang -
2 2015-12-22 Alfred Jiang -

方案名称

通知 - iOS7 的多任务处理——远程通知（Remote Notifications）

关键字

通知 \ 多任务处理 \ 后台获取数据 \ Background Fetch \ Remote Notification

需求场景

  1. 需要获取服务器的通知时

参考链接

  1. iOS 7系列译文：iOS7的多任务处理

详细内容

  1. 注册推送通知

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    - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
        [[UIApplication sharedApplication] registerForRemoteNotifications];
        return YES;
    }

  2. 处理一个推送通知

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    - (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);
    }

  3. 通过实现NSURLSessionDownloadDelegate的委托方法完成下载任务

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    #Pragma Mark - NSURLSessionDownloadDelegate

    - (void) URLSession:(NSURLSession *)session
    downloadTask:(NSURLSessionDownloadTask *)downloadTask
    didFinishDownloadingToURL:(NSURL *)location
    {
        NSLog(@"downloadTask:%@ didFinishDownloadingToURL:%@", downloadTask.taskDescription, location);
        // Copy file to your app's storage with NSFileManager
        // ...
        // Notify your UI
    }

    - (void) URLSession:(NSURLSession *)session
    downloadTask:(NSURLSessionDownloadTask *)downloadTask
    didResumeAtOffset:(int64_t)fileOffset
    expectedTotalBytes:(int64_t)expectedTotalBytes
    {

    }

    - (void) URLSession:(NSURLSession *)session
    downloadTask:(NSURLSessionDownloadTask *)downloadTask
    didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten
    totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite
    {

    }

任务完成下载时，你会得到一个磁盘上该文件的临时URL。你必须把这个文件移动或复制你的应用程序空间，因为当你从这个委托方法返回时，该文件将从临时存储中删除。

  1. 当后台会话任务完成后，如果需要打开程序，则实现如下代码
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    - (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();
        }
    }

不同于以往的委托回调，该应用程序委托会被调用两次，因为您的会话和任务委托可能会收到一系列消息。应用程序委托的 handleEventsForBackgroundURLSession 方法，在这些 NSURLSession 委托的消息发送前被调用，然后， URLSessionDidFinishEventsForBackgroundURLSession 被调用。在前面的方法中，储存了一个后台完成处理代码（completionHandler），并在后面的方法中调用该代码更新界面。

效果图

（无）

备注

（无）