首页 > 代码库 > IOS网络访问之NSURLSession
IOS网络访问之NSURLSession
NSURLSession是IOS7中新添加的网络访问接口，作用与NSURLConnection一致，在程序在前台时，NSURLSession与NSURLConnection可以互为替代工作。如果用户强制将程序关闭，NSURLSession会断掉。
NSURLSession中关键类有下面几种
1：NSURLSessionConfiguration：用于配置NSURLSession工作模式以及网络设置
工作模式分为下面三种：
普通模式（default）：可以使用缓存
+ (NSURLSessionConfiguration *)defaultSessionConfiguration;
瞬时模式（ephemeral）：不使用缓存
+ (NSURLSessionConfiguration *)ephemeralSessionConfiguration;
后台模式（background）：当按下home键后仍然可以在后台进行上传下载操作，需要通过唯一的identity标示
+ (NSURLSessionConfiguration *)backgroundSessionConfiguration:(NSString *)identifier;
网络设置：
@property BOOL allowsCellularAccess 允许使用蜂窝数据
@property (getter=isDiscretionary) BOOL discretionary YES时表示任务后台运行时自动选择最佳的网络选择（综合考虑网络，电量）
2：NSURLSession：获取NSURLSession有下面几种方式
+ (NSURLSession *)sharedSession 共享的会话，使用全局的Cookie，缓存数据
+ (NSURLSession *)sessionWithConfiguration:(NSURLSessionConfiguration *)configuration 使用配置好的NSURLSessionConfiguration获得会话
+ (NSURLSession *)sessionWithConfiguration:(NSURLSessionConfiguration *)configuration delegate:(id <NSURLSessionDelegate>)delegate delegateQueue:(NSOperationQueue *)queue 与第2中相似，但是指定了委托
3：NSURLSessionTask：会话任务，通过NSURLSession创建，有下面3种常用子类
NSURLSessionDataTask：最普通的网络访问，与NSURLConnection使用方式相似，多用来获取xml或者json，可以通过NSURLSession的以下方法创建
- (NSURLSessionDataTask *)dataTaskWithRequest:(NSURLRequest *)request;
- (NSURLSessionDataTask *)dataTaskWithURL:(NSURL *)url
同时还可以通过block指定回调
- (NSURLSessionDataTask *)dataTaskWithRequest:(NSURLRequest *)request completionHandler:(void (^)(NSData *data, NSURLResponse *response, NSError *error))completionHandler;
- (NSURLSessionDataTask *)dataTaskWithURL:(NSURL *)url completionHandler:(void (^)(NSData *data, NSURLResponse *response, NSError *error))completionHandler;
NSURLSessionDownLoadTask：用来处理下载任务
- (NSURLSessionDownloadTask *)downloadTaskWithRequest:(NSURLRequest *)request;
- (NSURLSessionDownloadTask *)downloadTaskWithURL:(NSURL *)url;
- (NSURLSessionDownloadTask *)downloadTaskWithResumeData:(NSData *)resumeData;
上面3种方法均可通过block设置回调，第三种方法可以实现断点续传
NSURLSessionUploadTask：用来处理上传任务，NSURLSessionDataTask的子类
- (NSURLSessionUploadTask *)uploadTaskWithRequest:(NSURLRequest *)request fromFile:(NSURL *)fileURL
- (NSURLSessionUploadTask *)uploadTaskWithRequest:(NSURLRequest *)request fromData:(NSData *)bodyData
- (NSURLSessionUploadTask *)uploadTaskWithStreamedRequest:(NSURLRequest *)request
上面3种方法同样可以通过block设置回调
创建后的NSURLSessionTask需要调用resume才会执行
4：NSURLSessionDelegate和NSURLSessionTaskDelegate协议
在网络请求的各个阶段都会触发协议的不同方法，具体使用方法可以参照后面例子
示例1：通过NSSessionDataTask访问网络数据
-(void)viewDidLoad { [super viewDidLoad]; NSString *urlStr = @"http://localhost/iostest.php"; urlStr = [urlStr stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]; //创建request NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:urlStr]]; request.HTTPMethod = @"POST"; request.HTTPBody = [@"name=zanglitao&gender=male" dataUsingEncoding:NSUTF8StringEncoding]; //创建NSURLSession NSURLSession *session = [NSURLSession sharedSession]; //创建任务 NSURLSessionDataTask *task = [session dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) { NSLog(@"%@",[[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding]); }]; //开始任务 [task resume];}
示例2：通过NSSessionUploadTask上传文件，流程和NSURLConnection基本一致，关键点也是设置请求头参数和请求体拼接
//自定义一个boundary#define boundary @"zanglitao"@interface ZViewController()@end@implementation ZViewController-(void)viewDidLoad { [super viewDidLoad]; NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL:[NSURL URLWithString:@"http://localhost/iostest.php"]]; //必须使用POST request.HTTPMethod = @"POST"; //设置请求体 request.HTTPBody = [self getDataBody]; //设置请求头 [request setValue:[NSString stringWithFormat:@"%d",[self getDataBody].length] forHTTPHeaderField:@"Content-Length"]; [request setValue:[NSString stringWithFormat:@"multipart/form-data; boundary=%@",boundary] forHTTPHeaderField:@"Content-Type"]; NSURLSession *session = [NSURLSession sharedSession]; NSURLSessionUploadTask *task = [session uploadTaskWithRequest:request fromData:[self getDataBody] completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) { NSLog(@"%@",[[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding]); }]; [task resume];}//获取请求体内容-(NSData *)getDataBody { NSMutableData *data =http://www.mamicode.com/ [NSMutableData data]; NSString *top = [NSString stringWithFormat:@"--%@\nContent-Disposition: form-data; name=\"file\"; filename=\"1.png\"\nContent-Type: image/png\n\n",boundary]; NSString *bottom = [NSString stringWithFormat:@"\n--%@--\n\n",boundary]; NSData *content = [NSData dataWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"1" ofType:@"png"]]; [data appendData:[top dataUsingEncoding:NSUTF8StringEncoding]]; [data appendData:content]; [data appendData:[bottom dataUsingEncoding:NSUTF8StringEncoding]]; return data;}@end
示例3：使用NSURLSessionDownLoadTask下载文件
-(void)viewDidLoad { [super viewDidLoad]; NSURLSession *session = [NSURLSession sharedSession]; NSURLSessionDownloadTask *task = [session downloadTaskWithURL:[NSURL URLWithString:@"http://g.hiphotos.baidu.com/image/pic/item/e61190ef76c6a7efc0a0e1ebfffaaf51f2de667c.jpg"] completionHandler:^(NSURL *location, NSURLResponse *response, NSError *error) { //下载完成后文件位于location处，我们需要移到沙盒中 NSString *dirPath = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) firstObject]; NSString *path = [dirPath stringByAppendingPathComponent:@"1.jpg"]; NSFileManager *manager = [NSFileManager defaultManager]; if ([manager fileExistsAtPath:path isDirectory:NO]) { [manager removeItemAtPath:path error:nil]; } [manager moveItemAtPath:[location path] toPath:path error:nil]; }]; //开始任务 [task resume];}
执行后我们看到沙盒中多了一张名为1.jpg的图片，这是我们下载的图片
上面的代码还有一点问题，就是下载过程中没有进度提示只能干等，我们可以通过设置委托获取下载进度
示例4：使用委托查看下载进度
@interface ZViewController()<NSURLSessionDelegate>@end@implementation ZViewController-(void)viewDidLoad { [super viewDidLoad]; NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration]; //使用配置的NSURLSessionConfiguration获取NSSession，并且设置委托 NSURLSession *session = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:nil]; NSURLSessionDownloadTask *task = [session downloadTaskWithURL:[NSURL URLWithString:@"http://g.hiphotos.baidu.com/image/pic/item/e61190ef76c6a7efc0a0e1ebfffaaf51f2de667c.jpg"] ]; //开始任务 [task resume];}- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWrittentotalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite { float percent = (float)totalBytesWritten/totalBytesExpectedToWrite; NSLog(@"%f",percent);}- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTaskdidFinishDownloadingToURL:(NSURL *)location { NSString *dirPath = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) firstObject]; NSString *path = [dirPath stringByAppendingPathComponent:@"1.jpg"]; NSFileManager *manager = [NSFileManager defaultManager]; if ([manager fileExistsAtPath:path isDirectory:NO]) { [manager removeItemAtPath:path error:nil]; } [manager moveItemAtPath:[location path] toPath:path error:nil];}//任务结束- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)taskdidCompleteWithError:(NSError *)error { NSLog(@"%s",__func__);}@end
2014-11-08 14:11:44.146 IOS网络请求[2366:3507] 0.020172
2014-11-08 14:11:44.147 IOS网络请求[2366:3507] 0.100307
2014-11-08 14:11:44.148 IOS网络请求[2366:3507] 0.153730
2014-11-08 14:11:44.148 IOS网络请求[2366:3507] 0.180442
2014-11-08 14:11:44.149 IOS网络请求[2366:3507] 0.207153
2014-11-08 14:11:44.150 IOS网络请求[2366:3507] 0.236461
2014-11-08 14:11:44.156 IOS网络请求[2366:3507] 0.263173
2014-11-08 14:11:44.160 IOS网络请求[2366:3507] 0.289884
2014-11-08 14:11:44.160 IOS网络请求[2366:3507] 0.316596
2014-11-08 14:11:44.161 IOS网络请求[2366:3507] 0.343307
2014-11-08 14:11:44.162 IOS网络请求[2366:3507] 0.370019
2014-11-08 14:11:44.162 IOS网络请求[2366:3507] 0.476865
2014-11-08 14:11:44.163 IOS网络请求[2366:3507] 0.557000
2014-11-08 14:11:44.169 IOS网络请求[2366:3803] 0.610423
2014-11-08 14:11:44.170 IOS网络请求[2366:3803] 0.663846
2014-11-08 14:11:44.171 IOS网络请求[2366:3803] 0.690558
2014-11-08 14:11:44.175 IOS网络请求[2366:3803] 0.717269
2014-11-08 14:11:44.176 IOS网络请求[2366:3803] 0.743981
2014-11-08 14:11:44.176 IOS网络请求[2366:3803] 0.797404
2014-11-08 14:11:44.177 IOS网络请求[2366:3803] 0.850827
2014-11-08 14:11:44.178 IOS网络请求[2366:3803] 0.877539
2014-11-08 14:11:44.179 IOS网络请求[2366:3803] 0.904250
2014-11-08 14:11:44.180 IOS网络请求[2366:3803] 0.930962
2014-11-08 14:11:44.180 IOS网络请求[2366:3803] 0.957674
2014-11-08 14:11:44.180 IOS网络请求[2366:3803] 0.984385
2014-11-08 14:11:44.181 IOS网络请求[2366:3803] 1.000000
2014-11-08 14:11:44.182 IOS网络请求[2366:3803] -[ZViewController URLSession:task:didCompleteWithError:]
下载是个漫长的过程，尤其是对于比较大的文件，所以我们还需要一个取消下载的按钮
示例5：示例4添加取消下载功能
@interface ZViewController()<NSURLSessionDelegate>@property(nonatomic,strong)NSURLSessionDownloadTask *task;@end@implementation ZViewController-(void)viewDidLoad { [super viewDidLoad]; NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration]; //使用配置的NSURLSessionConfiguration获取NSSession，并且设置委托 NSURLSession *session = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:nil]; _task = [session downloadTaskWithURL:[NSURL URLWithString:@"http://yinyueshiting.baidu.com/data2/music/46729925/13125209147600128.mp3?xcode=10d30604371d01ea5cfa24abb2db23a644b52c81891b10c8"] ]; //开始任务 [_task resume];}- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWrittentotalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite { float percent = (float)totalBytesWritten/totalBytesExpectedToWrite; NSLog(@"%f",percent);}- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTaskdidFinishDownloadingToURL:(NSURL *)location { NSString *dirPath = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) firstObject]; NSString *path = [dirPath stringByAppendingPathComponent:@"1.mp3"]; NSFileManager *manager = [NSFileManager defaultManager]; if ([manager fileExistsAtPath:path isDirectory:NO]) { [manager removeItemAtPath:path error:nil]; } [manager moveItemAtPath:[location path] toPath:path error:nil];}//任务结束- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)taskdidCompleteWithError:(NSError *)error { NSLog(@"%s",__func__);}- (IBAction)cancelDownload:(id)sender { [_task cancel];}@end
2014-11-08 14:25:28.351 IOS网络请求[2451:3803] 0.000917
2014-11-08 14:25:28.359 IOS网络请求[2451:3507] 0.008676
2014-11-08 14:25:28.370 IOS网络请求[2451:1303] 0.010250
2014-11-08 14:25:28.379 IOS网络请求[2451:5407] 0.018904
2014-11-08 14:25:28.393 IOS网络请求[2451:3507] 0.022838
2014-11-08 14:25:28.393 IOS网络请求[2451:3507] 0.023625
2014-11-08 14:25:28.405 IOS网络请求[2451:3507] 0.030705
2014-11-08 14:25:28.405 IOS网络请求[2451:3507] 0.034639
2014-11-08 14:25:28.409 IOS网络请求[2451:1303] 0.035032
2014-11-08 14:25:28.414 IOS网络请求[2451:5407] 0.035426
2014-11-08 14:25:28.436 IOS网络请求[2451:3507] 0.035819
2014-11-08 14:25:28.479 IOS网络请求[2451:3507] -[ZViewController URLSession:task:didCompleteWithError:]
当按下取消按钮时下载停止，同时任务结束的方法被触发
当然现实中更常见的方式是任务停止下载后还能恢复下载
示例6：暂停与恢复
- (IBAction)pauseDownload:(id)sender { [_task suspend];}- (IBAction)continueDownload:(id)sender { [_task resume];}
有时候我们暂停了任务然后退出了程序，如果希望下次进入程序后还能继续下载，那就需要实现断点下载功能，在NSURLConnection中可以利用请求头的Range参数实现断点下载，在NSURLSession中实现断点下载更加简单
示例7：断点下载
@interface ZViewController()<NSURLSessionDelegate>@property (strong, nonatomic)NSURLSessionDownloadTask *task;//存储已下载的数据@property(nonatomic,strong)NSData *data;@end@implementation ZViewController-(void)viewDidLoad { [super viewDidLoad]; NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration]; //使用配置的NSURLSessionConfiguration获取NSSession，并且设置委托 NSURLSession *session = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:nil]; _task = [session downloadTaskWithURL:[NSURL URLWithString:@"http://yinyueshiting.baidu.com/data2/music/46729925/13125209147600128.mp3?xcode=10d30604371d01ea5cfa24abb2db23a644b52c81891b10c8"] ]; //开始任务 [_task resume];}- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWrittentotalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite { float percent = (float)totalBytesWritten/totalBytesExpectedToWrite; NSLog(@"%f",percent);}- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTaskdidFinishDownloadingToURL:(NSURL *)location { NSString *dirPath = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) firstObject]; NSString *path = [dirPath stringByAppendingPathComponent:@"1.mp3"]; NSFileManager *manager = [NSFileManager defaultManager]; if ([manager fileExistsAtPath:path isDirectory:NO]) { [manager removeItemAtPath:path error:nil]; } [manager moveItemAtPath:[location path] toPath:path error:nil];}//任务结束- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)taskdidCompleteWithError:(NSError *)error { NSLog(@"%s",__func__);}- (IBAction)pauseDownload:(id)sender { [_task cancelByProducingResumeData:^(NSData *resumeData) { _task = nil; _data = resumeData; }];}- (IBAction)continueDownload:(id)sender { NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration]; NSURLSession *session = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:nil]; _task = [session downloadTaskWithResumeData:_data]; [_task resume];}@end
示例8：后台下载
@implementation ZViewController-(void)viewDidLoad { [super viewDidLoad]; NSURLSession *session = [self session]; NSURLSessionDownloadTask *task = [session downloadTaskWithURL:[NSURL URLWithString:@"http://yinyueshiting.baidu.com/data2/music/46729925/13125209147600128.mp3?xcode=10d30604371d01ea5cfa24abb2db23a644b52c81891b10c8"] ]; //开始任务 [task resume];}//后台会话(保证只有一个后台会话)-(NSURLSession *)session { static NSURLSession *session; static dispatch_once_t token; dispatch_once(&token, ^{ //后台下载 NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration backgroundSessionConfiguration:@"zang"]; configuration.discretionary = YES; //使用配置的NSURLSessionConfiguration获取NSSession，并且设置委托 session = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:nil]; }); return session;}- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWrittentotalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite { float percent = (float)totalBytesWritten/totalBytesExpectedToWrite; NSLog(@"%f",percent);}- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTaskdidFinishDownloadingToURL:(NSURL *)location { NSString *dirPath = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) firstObject]; NSString *path = [dirPath stringByAppendingPathComponent:@"1.mp3"]; NSFileManager *manager = [NSFileManager defaultManager]; if ([manager fileExistsAtPath:path isDirectory:NO]) { [manager removeItemAtPath:path error:nil]; } [manager moveItemAtPath:[location path] toPath:path error:nil];}//任务结束- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)taskdidCompleteWithError:(NSError *)error { NSLog(@"%s",__func__);}@end
启动程序后按下home键发现下载进度信息不再更新，静候片刻再进入程序发现沙盒中多了1.mp3，使用backgroundSessionConfiguration可以使我们的下载任务运行在后台
我们也可以通过委托在文件下载完后进行界面更新
示例9：后台下载任务监控
当在后台下载完成后会触发AppDelegate的
- (void)application:(UIApplication *)application handleEventsForBackgroundURLSession:(NSString *)identifier completionHandler:(void (^)())completionHandler方法
- (void)application:(UIApplication *)application handleEventsForBackgroundURLSession:(NSString *)identifier completionHandler:(void (^)())completionHandler { NSLog(@"%@:download complete",identifier); self.handler = completionHandler;}
此方法包含一个competionHandler（此操作表示应用完成所有处理工作），通常我们会保存此对象；直到最后一个任务完成，此时会重新通过会话标识（上面sessionConfig中设置的）找到对应的会话并调用NSURLSession的-(void)URLSessionDidFinishEventsForBackgroundURLSession:(NSURLSession *)session代理方法，在这个方法中通常可以进行UI更新，并调用completionHandler通知系统已经完成所有操作
@implementation ZViewController-(void)viewDidLoad { [super viewDidLoad]; NSURLSession *session = [self session]; NSURLSessionDownloadTask *task = [session downloadTaskWithURL:[NSURL URLWithString:@"http://yinyueshiting.baidu.com/data2/music/46729925/13125209147600128.mp3?xcode=10d30604371d01ea5cfa24abb2db23a644b52c81891b10c8"] ]; //开始任务 [task resume];}//后台会话(保证只有一个后台会话)-(NSURLSession *)session { static NSURLSession *session; static dispatch_once_t token; dispatch_once(&token, ^{ //后台下载 NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration backgroundSessionConfiguration:@"zang"]; configuration.discretionary = YES; //使用配置的NSURLSessionConfiguration获取NSSession，并且设置委托 session = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:nil]; }); return session;}- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWrittentotalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite { float percent = (float)totalBytesWritten/totalBytesExpectedToWrite; NSLog(@"%f",percent);}- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTaskdidFinishDownloadingToURL:(NSURL *)location { NSLog(@"%s",__func__); NSString *dirPath = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) firstObject]; NSString *path = [dirPath stringByAppendingPathComponent:@"1.mp3"]; NSFileManager *manager = [NSFileManager defaultManager]; if ([manager fileExistsAtPath:path isDirectory:NO]) { [manager removeItemAtPath:path error:nil]; } [manager moveItemAtPath:[location path] toPath:path error:nil];}//任务结束- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)taskdidCompleteWithError:(NSError *)error { NSLog(@"%s",__func__);}- (void)URLSessionDidFinishEventsForBackgroundURLSession:(NSURLSession *)session { NSLog(@"%s",__func__); ZLTAppDelegate *appDelegate = (ZLTAppDelegate *)[UIApplication sharedApplication].delegate; void(^handler)() = appDelegate.handler; appDelegate.handler = nil; handler();}@end
2014-11-08 16:35:38.553 IOS网络请求[5149:1303] 0.018046
2014-11-08 16:35:38.554 IOS网络请求[5149:1303] 0.018117
2014-11-08 16:35:38.632 IOS网络请求[5149:3d07] 0.036427
2014-11-08 16:35:38.633 IOS网络请求[5149:3d07] 0.036606
2014-11-08 16:35:38.719 IOS网络请求[5149:4707] 0.054916
2014-11-08 16:35:38.719 IOS网络请求[5149:4707] 0.055094
2014-11-08 16:35:38.813 IOS网络请求[5149:1303] 0.073583
2014-11-08 16:35:38.814 IOS网络请求[5149:1303] 0.092072
2014-11-08 16:35:38.881 IOS网络请求[5149:3d07] 0.110560
2014-11-08 16:35:46.697 IOS网络请求[5149:607] zang:download complete
2014-11-08 16:35:46.701 IOS网络请求[5149:1303] -[ZViewController URLSession:downloadTask:didFinishDownloadingToURL:]
2014-11-08 16:35:46.703 IOS网络请求[5149:1303] -[ZViewController URLSession:task:didCompleteWithError:]
2014-11-08 16:35:46.703 IOS网络请求[5149:1303] -[ZViewController URLSessionDidFinishEventsForBackgroundURLSession:]
执行程序后按下home键，静静等待下载完成后发现虽然程序处于后台，但委托的3个方法均得到了执行
IOS网络访问之NSURLSession