如何防止恢复重复的NSURLSessionTask

Question

我正在尝试在我的项目中使用NSURLSession。情况是这样的，我想检查是否已经存在具有相同请求的任务。因此，我使用getTasksWithCompletionHandler进行检查，如果没有，则恢复块中的任务。但当我这样做时，数组中总是没有其他任务。

我错过了什么吗？

下面是我的代码：

#import "HttpRequestHelper.h"


@implementation HttpRequestHelper

+(NSURLSession *)sharedDefaultSession{
static dispatch_once_t once;
static NSURLSession * defaultSession;
dispatch_once(&once, ^{
    NSURLSessionConfiguration * configure = [NSURLSessionConfiguration defaultSessionConfiguration];
    configure.HTTPMaximumConnectionsPerHost = 5;
    configure.timeoutIntervalForRequest = kTimeOutInterval;
    configure.timeoutIntervalForResource = kTimeOutInterval;
    defaultSession = [NSURLSession sessionWithConfiguration:configure delegate:nil delegateQueue:[NSOperationQueue mainQueue]];
});

return defaultSession;
}

+(void)resultFromRequest:(NSURLRequest *)request withCompleter:(downloadCompleter)completer{

NSURLSessionDataTask * dataTask = [[self sharedDefaultSession] dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
//            NSLog(@"response %@",response);
//            NSLog(@"url:%@\nData:%@",request.URL,[[NSString alloc]initWithData:data encoding:NSUTF8StringEncoding]);
    if (!error) {
        NSHTTPURLResponse * httpResponse = (NSHTTPURLResponse *)response;
        if (httpResponse.statusCode == 200) {
            completer([self jsonObjectFromData:data]);
        } else {
            completer(nil);
            // handle http error
        }
    } else {
        completer(nil);
        NSLog(@"network error %@",error.localizedDescription);
        // handle network error
    }
}];

NSLog(@"check %@",dataTask);
[self checkAndResumeTask:dataTask];
}

+(void)checkAndResumeTask:(NSURLSessionTask *)task{
[[self sharedDefaultSession] getTasksWithCompletionHandler:^(NSArray *dataTasks, NSArray *uploadTasks, NSArray *downloadTasks) {
    BOOL isNewTask = (![self containTask:task inTaskArray:dataTasks]&&![self containTask:task inTaskArray:downloadTasks]);
    NSLog(@"isNewTask : %d %@",isNewTask,[self sharedDefaultSession] );
    if (isNewTask) {
        if (!IS_LOWER_IOS8) {
            task.priority = NSURLSessionTaskPriorityHigh;
        }
        NSLog(@"%@ resume",task);
        [task resume];
    } else {
        [task cancel];
    }
}];
}

+(BOOL)containTask:(NSURLSessionTask *)task inTaskArray:(NSArray *)taskArray{
NSString * taskIndepentId = [task.originalRequest valueForHTTPHeaderField:IndependentID]?:@"";
NSString * taskUrlString = task.originalRequest.URL.absoluteString;
for (NSURLSessionTask * oldTask in taskArray) {
    if (!IS_LOWER_IOS8) {
        oldTask.priority = NSURLSessionTaskPriorityDefault;
    }

    NSString * oldTaskIndepentId = [oldTask.originalRequest valueForHTTPHeaderField:IndependentID]?:@"";
    NSString * oldTaskUrlString = oldTask.originalRequest.URL.absoluteString;
    if ([taskIndepentId isEqualToString:oldTaskIndepentId] && [taskUrlString isEqualToString:oldTaskUrlString] && oldTask!=task) {
        return YES;
    }
}
return NO;
}

+(id)jsonObjectFromData:(NSData*)data{

NSError * dataError;
NSDictionary * dic =   [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&dataError];
if (dataError) {
    NSLog(@"json data error : %@",dataError);
}
return dic;
}

+(void)cancelTaskForRequest:(NSURLRequest *)request{
[[self sharedDefaultSession] getTasksWithCompletionHandler:^(NSArray *dataTasks, NSArray *uploadTasks, NSArray *downloadTasks) {
    [self cancelRequest:request ForArrayTasks:dataTasks];
    [self cancelRequest:request ForArrayTasks:uploadTasks];
    [self cancelRequest:request ForArrayTasks:downloadTasks];
}];
}

+(void)cancelRequest:(NSURLRequest *)request ForArrayTasks:(NSArray *)arrayTasks{
for (NSURLSessionTask * task in arrayTasks) {
    NSLog(@"task %@",task);
    NSURLRequest * requestTask = task.originalRequest;
    BOOL isSameURL = [requestTask.URL.absoluteString isEqualToString:request.URL.absoluteString];
    BOOL isSameID = [[requestTask valueForHTTPHeaderField:IndependentID] isEqualToString:[request valueForHTTPHeaderField:IndependentID]];
    if (isSameURL && isSameID) {
        [task cancel];
    }
}
}

@end

我已经尝试在检查checkAndResumeTask:之前添加[dataTask resume];，任务将在getTasksWithCompletionHandler中的数组中，但我如何在恢复之前进行检查？

这是正确的做法吗？

我将感谢任何意见，谢谢。

-编辑

@dgatwood :我确定另一个任务正在运行

+(void)checkAndResumeTask:(NSURLSessionTask *)task{
NSLog(@"\ncheck task %@ \nfor URL %@ \nin thread %@",task,task.originalRequest.URL.absoluteString,[NSOperationQueue currentQueue]);
[[self sharedDefaultSession] getTasksWithCompletionHandler:^(NSArray *dataTasks, NSArray *uploadTasks, NSArray *downloadTasks) {
    NSLog(@"\ncheck task %@ \nfor URL %@ \nin thread %@ \n\n old tasks: %@,\n%@",task,task.originalRequest.URL.absoluteString,[NSOperationQueue currentQueue],dataTasks,downloadTasks);
    BOOL isNewTask = (![self containTask:task inTaskArray:dataTasks]&&![self containTask:task inTaskArray:downloadTasks]);
    NSLog(@"isNewTask : %d %@",isNewTask,[self sharedDefaultSession] );
    if (isNewTask) {
        if (!IS_LOWER_IOS8) {
            task.priority = NSURLSessionTaskPriorityHigh;
        }
        [task resume];
        NSLog(@"\nresume task :%@",task);
    } else {
        [task cancel];
    }
}];
}

我在代码中打印信息，在块之前、块之后和恢复任务之后。

我用同样的请求调用了三个任务。

下面是我的结果

您可以在2015-09-04 01:59:45.216 XXX[26387:1632660] **resume task :<__NSCFLocalDataTask: 0x7fa428e81a40>{ taskIdentifier: 1 } { running }**之后看到此任务正在运行，但在此之后返回的块在数组中仍然没有任务。

这是因为在第一个任务恢复之前，块已经获得了数组吗？或者是我做错了什么？

2015-09-04 01:59:45.130 XXX[26387:1632660] 
check task <__NSCFLocalDataTask: 0x7fa428e81a40>{ taskIdentifier: 1 } { suspended } 
for URL https://XXX/AppApi/api/account/BonusDetails 
in thread <NSOperationQueue: 0x7fa428d05f70>{name = 'NSOperationQueue Main Queue'}
2015-09-04 01:59:45.131 XXX[26387:1632660] 
check task <__NSCFLocalDataTask: 0x7fa42b034e70>{ taskIdentifier: 2 } { suspended } 
for URL https://XXX/AppApi/api/account/BonusDetails 
in thread <NSOperationQueue: 0x7fa428d05f70>{name = 'NSOperationQueue Main Queue'}
2015-09-04 01:59:45.132 XXX[26387:1632660] 
check task <__NSCFLocalDataTask: 0x7fa42b037180>{ taskIdentifier: 3 } { suspended } 
for URL https://XXX/AppApi/api/account/BonusDetails 
in thread <NSOperationQueue: 0x7fa428d05f70>{name = 'NSOperationQueue Main Queue'}
2015-09-04 01:59:45.215 XXX[26387:1632660] 
check task <__NSCFLocalDataTask: 0x7fa428e81a40>{ taskIdentifier: 1 } { suspended } 
for URL https://XXX/AppApi/api/account/BonusDetails 
in thread <NSOperationQueue: 0x7fa428d05f70>{name = 'NSOperationQueue Main Queue'} 

 old tasks: (
),
(
)
2015-09-04 01:59:45.216 XXX1632660] isNewTask : 1 <__NSURLSessionLocal: 0x7fa428e80d80>
2015-09-04 01:59:45.216 XXX[26387:1632660] 
**resume task :<__NSCFLocalDataTask: 0x7fa428e81a40>{ taskIdentifier: 1 } { running }**
2015-09-04 01:59:45.255 XXX[26387:1632660] 
check task <__NSCFLocalDataTask: 0x7fa42b034e70>{ taskIdentifier: 2 } { suspended } 
for URL XXX/AppApi/api/account/BonusDetails 
in thread <NSOperationQueue: 0x7fa428d05f70>{name = 'NSOperationQueue Main Queue'} 

 old tasks: (
),
(
)
2015-09-04 01:59:45.255 XXX[26387:1632660] isNewTask : 1 <__NSURLSessionLocal: 0x7fa428e80d80>
2015-09-04 01:59:45.255 XXX[26387:1632660] 
resume task :<__NSCFLocalDataTask: 0x7fa42b034e70>{ taskIdentifier: 2 } { running }
2015-09-04 01:59:45.256 XXX[26387:1632660] 
check task <__NSCFLocalDataTask: 0x7fa42b037180>{ taskIdentifier: 3 } { suspended } 
for URL https://XXX/AppApi/api/account/BonusDetails 
in thread <NSOperationQueue: 0x7fa428d05f70>{name = 'NSOperationQueue Main Queue'} 

 old tasks: (
),
(
)

Answer 1

是否确定其他任务仍在运行？一旦任务完成，它就不会出现在对getTasksWithCompletionHandler的调用中。如果您需要检查以前的请求是否存在，甚至在它们完成之后，您将需要将原始URL或URL请求存储在NSSet或类似的文件中。