'AFNetworking'，'2.0.0'来下载数据。'AFNetworking'，'2.0.0'的内容。AFHTTPSessionManager或AFURLSessionManager。若要在 iOS 7 或更高版本上下载背景中的内容，我使用 NSURLSession 和它的 NSURLSessionDownloadTask。
打开 ProjectNavigator->YourProject->YourTarget->Capabilities（选项卡）->Background Modes 中的 BackgroundMode
在您的 AppDelegate 方法 - (BOOL)application:(UIApplication* )application didFinishLaunchingWithOptions:(NSDictionary* )launchOptions 中添加一个用于 NSURLSessin 的初始化器，代码如下：
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]];
session属性:@property (nonatomic, strong) NSURLSession session;
还需添加完成处理程序属性（如果您希望在应用程序终止或崩溃后获取后台下载进程的回调，则需要此属性）：
@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;
}
声明你的类（例如在AppDelegate.h文件中）符合协议NSURLSessionDelegate，像这样：
@interface AppDelegate : UIResponder <UIApplicationDelegate, NSURLSessionDelegate>
然后在某个地方添加下载任务：
NSURLSessionDownloadTask *task = [self.session downloadTaskWithURL:[NSURL URLWithString:urlString]];
task.taskDescription = [NSString stringWithFormat:@"Downloading file %@", [urlString lastPathComponent]];
[task resume];
当您的应用程序在终止后重新启动时，您的会话将被恢复并触发委托方法。同样，如果您的应用程序从后台唤醒到前台，您的应用程序委托方法也将被触发。
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，请使用以下内容：
[operation pause];
[operation resume];