URLSessionDidFinishEventsForBackgroundURLSession 未调用-Objective-C
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【中文标题】URLSessionDidFinishEventsForBackgroundURLSession 未调用-Objective-C【英文标题】:URLSessionDidFinishEventsForBackgroundURLSession Not Calling- Objective-C 【发布时间】:2015-09-20 06:07:11 【问题描述】:NSURLSession
委托方法 URLSessionDidFinishEventsForBackgroundURLSession
没有调用?
我已经在项目功能设置中启用了后台模式。
这里是代码
AppDelegate.h方法
@interface AppDelegate : UIResponder <UIApplicationDelegate>
@property (strong, nonatomic) UIWindow *window;
@property (nonatomic, copy) void(^backgroundTransferCompletionHandler)();
@end
AppDelegate.m方法
-(void)application:(UIApplication *)application handleEventsForBackgroundURLSession:(NSString *)identifier completionHandler:(void (^)())completionHandler
self.backgroundTransferCompletionHandler = completionHandler;
ViewController.m方法
- (void)viewDidLoad
[super viewDidLoad];
//Urls
[self initializeFileDownloadDataArray];
NSArray *URLs = [[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask];
self.docDirectoryURL = [URLs objectAtIndex:0];
NSURLSessionConfiguration *sessionConfiguration = [NSURLSessionConfiguration backgroundSessionConfiguration:@"com.GACDemo"];
sessionConfiguration.HTTPMaximumConnectionsPerHost = 5;
self.session = [NSURLSession sessionWithConfiguration:sessionConfiguration
delegate:self
delegateQueue:nil];
NSUrlSession 方法
-(void)URLSessionDidFinishEventsForBackgroundURLSession:(NSURLSession *)session
AppDelegate *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];
];
];
我可以一一下载所有文件,但是下载完所有文件后,URLSessionDidFinishEventsForBackgroundURLSession
方法没有调用。
仅在下载所有文件后,我必须执行一些操作方法。
【问题讨论】:
顺便说一句,我觉得getTasksWithCompletionHandler
的使用很奇怪,因为URLSessionDidFinishEvents...
只有在任务完成时才会被调用。这对我来说似乎是多余的(尽管可能与您手头的问题无关)。如果这种情况发生,调用handleEventsForBackgroundURLSession
,然后调用URLSessionDidFinish...
,你就有了一条不调用completionHandler
的路径。我认为这条路永远不会实现,但如果实现了,你就会引入一个新问题。
其实这是我第一次使用 NSUrlSession 类。我的实际要求是一旦下载(所有图像)完成,那么只有我可以从文档目录中检索图像并且我可以在 UICollectionVeiw 中显示
我正在关注 APPCODA 的本教程。这是链接appcoda.com/background-transfer-service-ios7
我看了那个教程,我认为它总体上很好,尽管我不同意URLSessionDidFinishEventsForBackgroundURLSession
的实现,正如我上面提到的。但我认为这不是你的问题。
【参考方案1】:
在以下情况下不会调用这些委托方法:
任务完成时应用程序已经在运行;
通过双击设备的主页按钮并手动将其终止,应用程序被终止;或
如果您无法启动具有相同标识符的后台NSURLSession
。
所以,显而易见的问题是:
应用程序是如何终止的?如果没有终止,或者如果终止不正确(例如,您通过双击主页按钮手动终止它),这将阻止调用这些委托方法。
你看到handleEventsForBackgroundURLSession
被调用了吗?
您是在物理设备上执行此操作吗?这在模拟器上表现不同。
归根结底,这里不足以诊断确切的问题,但这些是可能无法调用委托方法的常见原因。
你后来说:
其实这是我第一次使用
NSURLSession
类。我的实际要求是一旦下载(所有图像)完成,那么只有我可以从文档目录中检索图像,我可以显示在UICollectionView
。我正在学习 APPCODA 的本教程。这是链接http://appcoda.com/background-transfer-service-ios7
如果这是您的要求,那么后台 NSURLSession
可能会过大。它比标准的NSURLSession
慢,而且更复杂。如果您确实需要在应用暂停/终止后在后台继续进行大量下载,请仅使用后台会话。
您参考的那个教程似乎是对一个相当复杂的主题的通俗介绍(尽管我不同意 URLSessionDidFinish...
实现,如 cmets 中所讨论的那样)。我会这样做:
- (void)URLSessionDidFinishEventsForBackgroundURLSession:(NSURLSession *)session
// log message so we can see completion in device log; remove this once you're done testing the app
NSLog(@"%s", __FUNCTION__);
// Since you may be testing whether the terminated app is awaken when the
// downloads are done, you might want to post local notification.
// (Otherwise, since you cannot use the debugger, you're just staring
// at the device console hoping you see your log messages.) Local notifications
// are very useful in testing this, so you can see when this method is
// called, even if the app wasn't running. Obviously, you have to register
// for local notifications for this to work.
//
// UILocalNotification *notification = [[UILocalNotification alloc] init];
// notification.fireDate = [NSDate date];
// notification.alertBody = [NSString stringWithFormat:NSLocalizedString(@"Downloads done", nil. nil)];
//
// [[UIApplication sharedApplication] scheduleLocalNotification:notification];
// finally, in `handleEventsForBackgroundURLSession` you presumably
// captured the `completionHandler` (but did not call it). So this
// is where you'd call it on the main queue. I just have a property
// of this class in which I saved the completion handler.
dispatch_async(dispatch_get_main_queue(), ^
if (self.savedCompletionHandler)
self.savedCompletionHandler();
self.savedCompletionHandler = nil;
);
我心中的问题是,如果您只是为收藏视图下载图像,您是否真的需要后台会话。只有在应用程序仍在运行时无法合理下载的图像太多(或太大)时,我才会这样做。
为了完整起见,我将在下面分享后台下载的完整演示:
// AppDelegate.m
#import "AppDelegate.h"
#import "SessionManager.h"
@interface AppDelegate ()
@end
@implementation AppDelegate
// other app delegate methods implemented here
// handle background task, starting session and saving
// completion handler
- (void)application:(UIApplication *)application handleEventsForBackgroundURLSession:(NSString *)identifier completionHandler:(void (^)())completionHandler
[SessionManager sharedSession].savedCompletionHandler = completionHandler;
@end
和
// SessionManager.h
@import UIKit;
@interface SessionManager : NSObject
@property (nonatomic, copy) void (^savedCompletionHandler)();
+ (instancetype)sharedSession;
- (void)startDownload:(NSURL *)url;
@end
和
// SessionManager.m
#import "SessionManager.h"
@interface SessionManager () <NSURLSessionDownloadDelegate, NSURLSessionDelegate>
@property (nonatomic, strong) NSURLSession *session;
@end
@implementation SessionManager
+ (instancetype)sharedSession
static id sharedMyManager = nil;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^
sharedMyManager = [[self alloc] init];
);
return sharedMyManager;
- (instancetype)init
self = [super init];
if (self)
NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:@"foo"];
self.session = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:nil];
return self;
- (void)startDownload:(NSURL *)url
[self.session downloadTaskWithURL:url];
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location
NSLog(@"%s: %@", __FUNCTION__, downloadTask.originalRequest.URL.lastPathComponent);
NSError *error;
NSURL *documents = [[NSFileManager defaultManager] URLForDirectory:NSDocumentDirectory inDomain:NSUserDomainMask appropriateForURL:nil create:false error:&error];
NSAssert(!error, @"Docs failed %@", error);
NSURL *localPath = [documents URLByAppendingPathComponent:downloadTask.originalRequest.URL.lastPathComponent];
if (![[NSFileManager defaultManager] moveItemAtURL:location toURL:localPath error:&error])
NSLog(@"move failed: %@", error);
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error
NSLog(@"%s: %@ %@", __FUNCTION__, error, task.originalRequest.URL.lastPathComponent);
- (void)URLSessionDidFinishEventsForBackgroundURLSession:(NSURLSession *)session
NSLog(@"%s", __FUNCTION__);
// UILocalNotification *notification = [[UILocalNotification alloc] init];
// notification.fireDate = [NSDate date];
// notification.alertBody = [NSString stringWithFormat:NSLocalizedString(@"Downloads done", nil. nil)];
//
// [[UIApplication sharedApplication] scheduleLocalNotification:notification];
if (self.savedCompletionHandler)
self.savedCompletionHandler();
self.savedCompletionHandler = nil;
@end
最后是发起请求的视图控制器代码:
// ViewController.m
#import "ViewController.h"
#import "SessionManager.h"
@implementation ViewController
- (IBAction)didTapButton:(id)sender
NSArray *urlStrings = @[@"http://spaceflight.nasa.gov/gallery/images/apollo/apollo17/hires/s72-55482.jpg",
@"http://spaceflight.nasa.gov/gallery/images/apollo/apollo10/hires/as10-34-5162.jpg",
@"http://spaceflight.nasa.gov/gallery/images/apollo-soyuz/apollo-soyuz/hires/s75-33375.jpg",
@"http://spaceflight.nasa.gov/gallery/images/apollo/apollo17/hires/as17-134-20380.jpg",
@"http://spaceflight.nasa.gov/gallery/images/apollo/apollo17/hires/as17-140-21497.jpg",
@"http://spaceflight.nasa.gov/gallery/images/apollo/apollo17/hires/as17-148-22727.jpg"];
for (NSString *urlString in urlStrings)
NSURL *url = [NSURL URLWithString:urlString];
[[SessionManager sharedSession] startDownload:url];
// explicitly kill app if you want to test background operation
//
// exit(0);
- (void)viewDidLoad
[super viewDidLoad];
// if you're going to use local notifications, you must request permission
UIUserNotificationSettings *settings = [UIUserNotificationSettings settingsForTypes:UIUserNotificationTypeAlert categories:nil];
[[UIApplication sharedApplication] registerUserNotificationSettings:settings];
@end
【讨论】:
其实这是我第一次使用 NSUrlSession 类。我的实际要求是一旦下载(所有图像)完成,那么只有我可以从文档目录中检索图像并且我可以在 UICollectionVeiw 中显示。我正在关注 APPCODA 的本教程。这是链接 appcoda.com/background-transfer-service-ios7 – @Rob 该方法永远不会在模拟器(9.2)中被调用。但是我还没有在设备上测试过。 @RajanMaheshwari 是的,我建议在设备上进行测试。在设备上,它确实会被调用。 这非常有帮助!【参考方案2】:正如苹果所说:
如果 iOS 应用程序被系统终止并重新启动,该应用程序可以使用相同的标识符来创建新的配置对象和会话,并检索终止时正在进行的传输状态。此行为仅适用于系统正常终止应用程序。如果用户从多任务屏幕终止应用程序,系统将取消会话的所有后台传输。此外,系统不会自动重新启动用户强制退出的应用程序。用户必须明确地重新启动应用程序才能重新开始传输。
【讨论】:
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