我正在使用'AFNetworking', '2.0.0' 下载数据。
我需要下载大文件。当用户锁定屏幕或按下主页按钮时，它应该暂停（或在后台继续下载），如果我返回应用程序，它应该恢复。
我还需要显示下载进度。
我搜索了很多示例，但没有找到任何东西 'AFNetworking', '2.0.0'。
我为 iOS 6.0+ 版本创建应用程序，所以我不能使用 AFHTTPSessionManager 或 AFURLSessionManager。
【问题讨论】：
标签： ios objective-c afnetworking-2
为了在 iOS 7 或更高版本的后台下载，我使用NSURLSession 和他们的NSURLSessionDownloadTask。
在 ProjectNavigator->YourProject->YourTarget->Capabilities (tab)->Background Modes 中打开 BackgroundMode
将NSURLSessin 的初始化器添加到您的 AppDelegate 方法 - (BOOL)application:(UIApplication* )application didFinishLaunchingWithOptions:(NSDictionary* )launchOptions 和下一个代码：
NSURLSessionConfiguration *sessionConfiguration;
NSString *someUniqieIdentifierForSession = @"com.etbook.background.DownloadManager";
if ([[[[[UIDevice currentDevice] systemVersion] componentsSeparatedByString:@"."] firstObject] integerValue] >= 8) {
//This code for iOS 8 and greater
sessionConfiguration = [NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:someUniqieIdentifierForSession];
} else {
this code for iOS 7
sessionConfiguration = [NSURLSessionConfiguration backgroundSessionConfiguration:someUniqieIdentifierForSession];
}
sessionConfiguration.HTTPMaximumConnectionsPerHost = 5;
self.session = [NSURLSession sessionWithConfiguration:sessionConfiguration
delegate:self
delegateQueue:[NSOperationQueue mainQueue]];
当然，不要忘记声明session 属性：
@property (nonatomic, strong) NSURLSession session;
还添加完成处理属性（如果您想在应用程序终止或崩溃后获取后台下载过程的回调，则需要它）：
@property (nonatomic, copy) void(^backgroundTransferCompletionHandler)();
在 AppDelegate 中添加委托方法：
-(void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location{
NSError *error;
NSFileManager *fileManager = [NSFileManager defaultManager];
NSString *destinationFilename = downloadTask.originalRequest.URL.lastPathComponent;
NSURL *destinationURL = [[[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject] URLByAppendingPathComponent:destinationFilename];
if ([fileManager fileExistsAtPath:[destinationURL path]]) {
[fileManager removeItemAtURL:destinationURL error:nil];
}
[fileManager copyItemAtURL:location
toURL:destinationURL
error:&error];
}
-(void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error{
if (error != nil) {
NSLog(@"Download completed with error: %@", [error localizedDescription]);
}
else{
NSLog(@"Download finished successfully.");
}
-(void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite{
if (totalBytesExpectedToWrite == NSURLSessionTransferSizeUnknown) {
NSLog(@"Unknown transfer size");
}
else{
NSLog(@"progress = %lld Mb of %lld Mb", totalBytesWritten/1024/1024, totalBytesExpectedToWrite/1024/1024);
}
}
-(void)URLSessionDidFinishEventsForBackgroundURLSession:(NSURLSession *)session{
ETBAppDelegate *appDelegate = [UIApplication sharedApplication].delegate;
// Check if all download tasks have been finished.
[self.session getTasksWithCompletionHandler:^(NSArray *dataTasks, NSArray *uploadTasks, NSArray *downloadTasks) {
if ([downloadTasks count] == 0) {
if (appDelegate.backgroundTransferCompletionHandler != nil) {
// Copy locally the completion handler.
void(^completionHandler)() = appDelegate.backgroundTransferCompletionHandler;
// Make nil the backgroundTransferCompletionHandler.
appDelegate.backgroundTransferCompletionHandler = nil;
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
// Call the completion handler to tell the system that there are no other background transfers.
completionHandler();
// Show a local notification when all downloads are over.
UILocalNotification *localNotification = [[UILocalNotification alloc] init];
localNotification.alertBody = @"All files have been downloaded!";
[[UIApplication sharedApplication] presentLocalNotificationNow:localNotification];
}];
}
}
}];
}
//Background download support (THIS IMPORTANT METHOD APPLICABLE ONLY IN YOUR AppDelegate.m FILE!!!)
-(void)application:(UIApplication *)application handleEventsForBackgroundURLSession:(NSString *)identifier completionHandler:(void (^)())completionHandler{
self.backgroundTransferCompletionHandler = completionHandler;
}
并声明您的类（在我的示例中的 AppDelegate.h 文件中）符合协议NSURLSessionDelegate，如下所示：
@interface AppDelegate : UIResponder <UIApplicationDelegate, NSURLSessionDelegate>
然后在某处添加下载任务：
NSURLSessionDownloadTask *task = [self.session downloadTaskWithURL:[NSURL URLWithString:urlString]];
task.taskDescription = [NSString stringWithFormat:@"Downloading file %@", [urlString lastPathComponent]];
[task resume];
因此，当您的应用程序在终止后启动时，您的会话将被恢复并且委托方法将被触发。此外，如果您的应用程序将从后台唤醒到前台，您的应用程序委托方法也将被触发。
【讨论】：
当您的应用程序进入后台暂停/停止下载操作时，当进入前台时恢复您在 NSOperation 队列中暂停的下载操作。 阅读这几行代码可能会对您有所帮助：
AFDownloadRequestOperation *operation = [[AFDownloadRequestOperation alloc] initWithRequest:request targetPath:filePath shouldResume:YES];
[operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
//handel completion
[operations removeObjectForKey:audioItem.filename];
}failure:^(AFHTTPRequestOperation *operation, NSError *error) {
//handel failure
operation = [operations objectForKey:audioItem.filename];
[operation cancel];
[operations removeObjectForKey:audioItem.filename];
if (error.code != NSURLErrorCancelled) {
[self showErrorAlert];
NSLog(@"Error: %@", error);
}
}];
[operation setProgressiveDownloadProgressBlock:^(NSInteger bytesRead, long long totalBytesRead, long long totalBytesExpected, long long totalBytesReadForFile, long long totalBytesExpectedToReadForFile) {
//handel progress
NSNumber *progress = [NSNumber numberWithFloat:((float)totalBytesReadForFile / (float)totalBytesExpectedToReadForFile)];
float progress=progress.floatValue;
[self performSelectorOnMainThread:@selector(updateProgressBar:) withObject:[NSArray arrayWithObjects:audioItem, progress, nil] waitUntilDone: YES];
}];
[operation setShouldExecuteAsBackgroundTaskWithExpirationHandler:^{
// TODO: Clean up operations
NSLog(@"App has been in background too long, need to clean up any connections!");
}];
[operations setValue:operation forKey:@"key"]; // store the NSOperation for further use in application to track its status.
[downloadQueue addOperation:operation];//here downloadQueue is NSOperationQueue instance that manages NSOperations.
要暂停下载操作，请使用：
[operation pause];
要恢复使用这种行：
[operation resume];
【讨论】：
也许您最好使用 DTDownload： https://github.com/Cocoanetics/DTDownload
据我所知，它没有任何可报告的进度。
编辑：AppCoda 上有一个很好的教程，关于使用 NSURLSessionTask： http://www.appcoda.com/background-transfer-service-ios7/
【讨论】：