objective-c - CKQueryOperation 处理大批量

Question

我在使用大批量数据创建 CKQuery 操作时遇到问题。我的查询适用于 100 个结果，但在更多结果查询失败后，因为一个线程调度错误或其他原因(libdispatch.dylib`dispatch_group_leave:) 我迷路了……有什么想法吗？

+ (void) fetchAnswersWithRecordId:(CKRecordID *)recordId completionHandler:(CloudKitCompletionHandler)handler {
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"ANSrecordID == %@", recordId];
CKQuery *query = [[CKQuery alloc] initWithRecordType:ckAnswers predicate:predicate];

CKQueryOperation *operation = [[CKQueryOperation alloc] initWithQuery:query];
CKQueryOperation * __weak weakSelf = operation;
operation.resultsLimit = 300;
NSMutableArray *tmp = [[NSMutableArray alloc] init];


operation.recordFetchedBlock = ^(CKRecord *record) {
    [tmp addObject:record];
};

operation.queryCompletionBlock = ^(CKQueryCursor *cursor, NSError *error) {
    if (!handler)
        return;

    NSArray *array = [NSArray arrayWithArray:tmp];
    if(cursor != nil) {
        CKQueryOperation *newOperation = [[CKQueryOperation alloc] initWithCursor:cursor];
        newOperation.recordFetchedBlock = weakSelf.recordFetchedBlock;
        newOperation.completionBlock = weakSelf.completionBlock;
        [[self publicCloudDatabase] addOperation:newOperation];
    } else {
        NSLog(@"Results: %lu", [array count]);
        dispatch_async(dispatch_get_main_queue(), ^{
            handler(array, error);
        });
    }
};

[[self publicCloudDatabase] addOperation:operation];}

Answer 1

我认为您的问题在于 __weak 操作以及您在另一个操作中创建操作的方式。这是一个示例(快速)，说明我如何做类似的事情，即获得额外的结果，但在获取而不是查询中。注意第一次使用实例变量初始化，通过GCD dispatch_aync使用半递归:

private func _fetchRecordChangesFromCloud() {
    if !_fetching {
        // this is the first and only time this code is called in GCD recusion

        // we clean the caches we use to collect the results of the fetch
        // so we can then save the record in the correct order so references can be created
        _fetchedModifiedRecords = []
        _fetchedDeletedRecordIDs = []

        // mark fetching has started
        _fetching = true
    }

    let operation = CKFetchRecordChangesOperation(recordZoneID: _customRecordZoneID, previousServerChangeToken: _serverChangeToken)

    operation.recordChangedBlock = { (record: CKRecord?) in
        if let record = record {
            println("Received record to save: \(record)")
            self._fetchedModifiedRecords.append(record)
        }
    }

    operation.recordWithIDWasDeletedBlock = { (recordID: CKRecordID?) in
        if let recordID = recordID {
            println("Received recordID to delete: \(recordID)")
            self._fetchedDeletedRecordIDs.append(recordID)
        }
    }

    operation.fetchRecordChangesCompletionBlock = {
        (serverChangeToken: CKServerChangeToken?, clientChangeToken: NSData?, error: NSError?) -> Void in

        if let error = error {
            println("Error in fetching record changes: \(error)")
            // try again next sync
            self._fetchAfterNextSuccessfullSync = true
            self._fetching = false
            return
        }

        // fetched records successfuly
        println("fetched records successfuly")

        if let serverChangeToken = serverChangeToken {
            self._serverChangeToken = serverChangeToken
        }

        if operation.moreComing {
            // we need to create another operation object and do it again
            dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)) {
                self._fetchRecordChangesFromCloud()
            }
        } else {
            // we are finally done

            // process the fetched records
            self._processFetchedRecords()

            // save all changes back to persistent store
            self._saveBackgroundContext()

            // we are done
            self._fetching = false
        }
    }

    self._privateDatabase.addOperation(operation)
}