NSInternalInconsistencyException運行後臺提取循環

Question

我有這段代碼試圖爲HealthKit數據做後臺提取。當我第一次運行應用程序時，代碼工作正常，但如果我手動執行後臺提取（使用調試命令），我會得到一個異常拋出，並說錯誤，說reason: 'this request has been neutered - you can't call -sendResponse: twice nor after encoding it'，我不知道爲什麼。

這裏是獲取數據的代碼：

- (void)fetchNewDataWithCompletionHandler:(void (^)(UIBackgroundFetchResult))completionHandler { 

    if (!self.healthStore) { 
     self.healthStore = [HKHealthStore new]; 
    } 

    dataTypes = [NSDictionary dictionaryWithObjectsAndKeys: 
       [NSNumber numberWithInt:1], HKQuantityTypeIdentifierStepCount, 
       [NSNumber numberWithInt:2], HKQuantityTypeIdentifierFlightsClimbed, 
       [NSNumber numberWithInt:3], HKQuantityTypeIdentifierDistanceWalkingRunning, 
       [NSNumber numberWithInt:4], HKQuantityTypeIdentifierDistanceCycling, nil]; 
    achievementData = [NSMutableDictionary new]; 

    NSCalendar *calendar = [NSCalendar currentCalendar]; 
    NSDate *startDate = [calendar startOfDayForDate:[NSDate date]]; 
    NSDate *endDate = [calendar dateByAddingUnit:NSCalendarUnitDay value:1 toDate:startDate options:0]; 
    NSPredicate *predicate = [HKQuery predicateForSamplesWithStartDate:startDate endDate:endDate options:HKQueryOptionNone]; 

    for (NSString *key in dataTypes) { 

     HKSampleType *sampleType = [HKSampleType quantityTypeForIdentifier:key]; 

     HKSampleQuery *query = [[HKSampleQuery alloc] initWithSampleType:sampleType predicate:predicate limit:HKObjectQueryNoLimit sortDescriptors:nil resultsHandler:^(HKSampleQuery *query, NSArray *results, NSError *error) { 

      if (!error) { 

       if (!results) { 

        NSLog(@"No results were returned form query"); 

        completionHandler(UIBackgroundFetchResultNoData); 

       } else { 

        dispatch_async(dispatch_get_main_queue(), ^{ 

         [self processNewDataWithResults:results andType:key]; 

         completionHandler(UIBackgroundFetchResultNewData); 

        }); 

       } 

      } else { 

       NSLog(@"Error: %@ %@", error, [error userInfo]); 

       completionHandler(UIBackgroundFetchResultFailed); 

      } 

     }]; 

     [self.healthStore executeQuery:query]; 

    } 

} 

然後，我有一個單獨的函數處理，你可以看到結果時，發現被調用的數據。如果你想我可以把它粘貼在這裏，但它很長，不知道它是否與它有任何關係。

我已經嘗試把斷點放在看看什麼時候完成處理程序被調用，但從我可以告訴它只被調用一次，除非我在這裏丟失了一些愚蠢的東西。

如果有人有任何建議，請讓我知道:)謝謝！

編輯 以下是錯誤消息是什麼樣子：

2015-05-13 10:11:54.467 appName[379:169163] *** Assertion failure in -[UIFetchContentInBackgroundAction sendResponse:], /SourceCache/BaseBoard/BaseBoard-98.3/BaseBoard/BSAction.m:221 
2015-05-13 10:11:54.470 appName[379:169163] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'this request has been neutered - you can't call -sendResponse: twice nor after encoding it' 
*** First throw call stack: 
(0x28ed4137 0x36e30c77 0x28ed400d 0x29bd2bc9 0x2dbde865 0x397ed5 0x2dbde7cf 0x2ca82a3d 0x39019b 0x390187 0x393e9d 0x28e99889 0x28e97fa9 0x28de39a1 0x28de37b3 0x305951a9 0x2c56e695 0xdff29 0x373d8aaf) 
libc++abi.dylib: terminating with uncaught exception of type NSException 

Answer 1

從看着你發佈的代碼，我沒有看到比背景提取完成處理任何其他方式將被準確地稱爲由於for循環而導致4次。

在HKSampleQuery每個實例的resultHandlers的代碼路徑將在任何情況下completionHandler(UIBackgroundFetchResult...)通話結束了，你總是實例他們四人，所以這是斷言'you can't call -sendResponse: twice'抱怨IMO。

通過註釋dataTypes字典中的3個查詢，應該很容易檢查這是否是問題。

編輯：作爲意見要求，這裏有一個可能的解決方案（..just了我的頭頂，所以把它與鹽糧..）：

它（一）使用將異步查詢結果回調變爲「同步」調用的信號量鎖（b）使用調度組等待所有4個查詢在執行完成處理程序之前完成。

// NOTE: This example assumes that the fetch has "new data" if any of the queries returned something 
//  Also it skips the 'NSError' part (which could work exactly like the 'result' var) 

// Define one or more block-global result variables for queries can put their end state into 
UIBackgroundFetchResult __block result = UIBackgroundFetchResultNoData; 

// Create a dispatch group that will manage all the concurrent queries 
dispatch_queue_t queue = dispatch_queue_create([@"my.query.queue" UTF8String], DISPATCH_QUEUE_CONCURRENT); 
dispatch_group_t queries = dispatch_group_create(); 

// For each dataType dispatch a group block containing the query to run on the concurrent queue 
for (NSString *key in dataTypes) { 
    dispatch_group_async(queries, queue, ^{ 
     // To work around the asynchronous callback, I'll use a lock to wait for the query to return their result, so.. 

     // ..like above, a block-global var will hold the result of the query 
     BOOL __block success = NO; 

     // ..create a one-time lock.. 
     dispatch_semaphore_t lock = dispatch_semaphore_create(0); 
     HKSampleQuery *query = [[HKSampleQuery alloc] initWithSampleType:sampleType predicate:predicate limit:HKObjectQueryNoLimit sortDescriptors:nil resultsHandler:^(HKSampleQuery *query, NSArray *results, NSError *error) { 
      success = YES; // ..or however you define success.. ;) 

      dispatch_semaphore_signal(lock); // ..open lock to signal result available.. 
     }]; 
     dispatch_semaphore_wait(lock, DISPATCH_TIME_FOREVER); // ..wait for callback result lock to open.. 

     // ..determine & set result. 
     if (success) { 
      result = UIBackgroundFetchResultNewData; 
     } 
    }); 
} 

// Schedule a final block to execute (on the main queue) when all the other group blocks have finished running 
dispatch_group_notify(queries, dispatch_get_main_queue(), ^{ 
    // Determine final result and call completion handler 
    completionHandler(result); 
});