变更记录

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 ```objective-c

2. (BOOL)application:(UIApplication )application didFinishLaunchingWithOptions:(NSDictionary )launchOptions { [[UIApplication sharedApplication] registerForRemoteNotifications]; return YES; } ```

3. 处理一个推送通知 ```objective-c

4. (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; }

5. (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); } ```

6. 通过实现NSURLSessionDownloadDelegate的委托方法完成下载任务 ```objective-c

   Pragma Mark - NSURLSessionDownloadDelegate

7. (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 }

8. (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。

4. 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
```objective-c
- (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

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