iphone - 使用 Parse 同步数据,而不是下载数据

标签 iphone ios cocoa-touch afnetworking parse-platform

我一直在关注 RayWenderlinch.com 的 How To Synchronize Core Data with a Web Service – Part 1 我正在尝试将其自定义到我的应用程序,但使用 AFNetworking 从 Parse 实际下载数据时遇到问题

应用程序应该连接解析,查看两个类“Club”和“IronSet”检查是否有新记录(或在初始运行时,抓取所有内容)并仅下载新添加的内容。

然后它将这些记录保存到核心数据中,然后从 Cache/JSONRecords/Club(或 IronSet)中删除文件。似乎我从未真正从 Parse 中获取数据,尽管它连接成功,并且在从缓存中删除文件之前不会引发错误。

我收到“所有操作已完成”,这表明 SyncEngine 应该已完成,并在 downloadDataForRegisteredObjects 中下载。

错误

2013-08-26 19:39:03.981 WGT Golf Calculator[3287:c07] All operations completed
2013-08-26 19:39:03.991 WGT Golf Calculator[3287:c07] Unable to delete JSON records at Club -- file://localhost/Users/**/Library/Application%20Support/iPhone%20Simulator/6.1/Applications/4B72F57E-264D-44F7-981D-3D921B0CC2A4/Library/Caches/JSONRecords/, reason Error Domain=NSCocoaErrorDomain Code=4 "The operation couldn’t be completed. (Cocoa error 4.)" UserInfo=0x75610f0 {NSUnderlyingError=0x75615e0 "The operation couldn’t be completed. No such file or directory", NSFilePath=/Users/**/Library/Application Support/iPhone Simulator/6.1/Applications/4B72F57E-264D-44F7-981D-3D921B0CC2A4/Library/Caches/JSONRecords/Club, NSUserStringVariant=(
    Remove
)}

MLVAppDelegate.m
#import "MLVAppDelegate.h"
#import "MLVSyncEngine.h"
#import "Club.h"
#import "IronSet.h"

@implementation MLVAppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    [[MLVSyncEngine sharedEngine] registerNSManagedObjectClassToSync:[Club class]];
    [[MLVSyncEngine sharedEngine] registerNSManagedObjectClassToSync:[IronSet class]];

    return YES;
}    

MLVAFParseAPIClient.h
#import "AFHTTPClient.h"

@interface MLVAFParseAPIClient : AFHTTPClient

+ (MLVAFParseAPIClient *)sharedClient;

- (NSMutableURLRequest *)GETRequestForClass:(NSMutableString *)className parameters:(NSDictionary *)parameters;

- (NSMutableURLRequest *)GETRequestForAllRecordsOfClass:(NSString *)className updatedAfterDate:(NSDate *)updatedDate;

@end

MLVAFParseAPIClient.m
#import "MLVAFParseAPIClient.h"
#import "AFJSONRequestOperation.h"

static NSString * const kSDFParseAPIBaseURLString = @"https://api.parse.com/1/";
static NSString * const kSDFParseAPIApplicationId = @"APP ID REMOVED";
static NSString * const kSDFParseAPIKey = @"API KEY REMOVED";

@implementation MLVAFParseAPIClient

+ (MLVAFParseAPIClient *)sharedClient
{
    static MLVAFParseAPIClient *sharedClient = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{sharedClient = [[MLVAFParseAPIClient alloc] initWithBaseURL:[NSURL URLWithString:kSDFParseAPIBaseURLString]];
    });

    return sharedClient;
}

- (id)initWithBaseURL:(NSURL *)url {
    self = [super initWithBaseURL:url];
    if (self) {
        [self registerHTTPOperationClass:[AFJSONRequestOperation class]];
        [self setParameterEncoding:AFJSONParameterEncoding];
        [self setDefaultHeader:@"X-Parse-Application-Id" value:kSDFParseAPIApplicationId];
        [self setDefaultHeader:@"X-Parse-REST-API-Key" value:kSDFParseAPIKey];
    }

    return self;
}

- (NSMutableURLRequest *)GETRequestForClass:(NSMutableString *)className parameters:(NSDictionary *)parameters
{
    NSMutableURLRequest *request = nil;
    request = [self requestWithMethod:@"GET" path:[NSString stringWithFormat:@"classes/%@", className] parameters:parameters ];
    return request;
}

- (NSMutableURLRequest *)GETRequestForAllRecordsOfClass:(NSString *)className updatedAfterDate:(NSDate *)updatedDate
{
    NSMutableURLRequest *request = nil;
    NSDictionary *parameters = nil;

    if (updatedDate) {
        NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
        [dateFormatter setDateFormat:@"yyyy-MM-dd'T'HH:mm:ss.'999Z'"];
        [dateFormatter setTimeZone:[NSTimeZone timeZoneWithName:@"GMT"]];

        NSString *jsonString = [NSString stringWithFormat:@"{\"updatedAt\":{\"$gte\":{\"__type\":\"Date\",\"iso\":\"%@\"}}}", [dateFormatter stringFromDate:updatedDate]];

        parameters = [NSDictionary dictionaryWithObject:jsonString forKey:@"where"];
    }

    request = [self GETRequestForClass:className parameters:parameters];
    return request;
}


@end

MLVCoreDataController.m
#import "MLVCoreDataController.h"

@interface MLVCoreDataController ()

@property (strong, nonatomic) NSManagedObjectContext *masterManagedObjectContext;
@property (strong, nonatomic) NSManagedObjectContext *backgroundManagedObjectContext;
@property (strong, nonatomic) NSManagedObjectModel *managedObjectModel;
@property (strong, nonatomic) NSPersistentStoreCoordinator *persistentStoreCoordinator;

@end

@implementation MLVCoreDataController

@synthesize masterManagedObjectContext = _masterManagedObjectContext;
@synthesize backgroundManagedObjectContext = _backgroundManagedObjectContext;
@synthesize managedObjectModel = _managedObjectModel;
@synthesize persistentStoreCoordinator = _persistentStoreCoordinator;

+ (id)sharedInstance {
    static dispatch_once_t once;
    static MLVCoreDataController *sharedInstance;
    dispatch_once(&once, ^{
        sharedInstance = [[self alloc] init];
    });

    return sharedInstance;
}

#pragma mark - Core Data stack

// Used to propegate saves to the persistent store (disk) without blocking the UI
- (NSManagedObjectContext *)masterManagedObjectContext {
    if (_masterManagedObjectContext != nil) {
        return _masterManagedObjectContext;
    }

    NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
    if (coordinator != nil) {
        _masterManagedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
        [_masterManagedObjectContext performBlockAndWait:^{
            [_masterManagedObjectContext setPersistentStoreCoordinator:coordinator];
        }];

    }
    return _masterManagedObjectContext;
}

// Return the NSManagedObjectContext to be used in the background during sync
- (NSManagedObjectContext *)backgroundManagedObjectContext {
    if (_backgroundManagedObjectContext != nil) {
        return _backgroundManagedObjectContext;
    }

    NSManagedObjectContext *masterContext = [self masterManagedObjectContext];
    if (masterContext != nil) {
        _backgroundManagedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
        [_backgroundManagedObjectContext performBlockAndWait:^{
            [_backgroundManagedObjectContext setParentContext:masterContext];
        }];
    }

    return _backgroundManagedObjectContext;
}

// Return the NSManagedObjectContext to be used in the background during sync
- (NSManagedObjectContext *)newManagedObjectContext {
    NSManagedObjectContext *newContext = nil;
    NSManagedObjectContext *masterContext = [self masterManagedObjectContext];
    if (masterContext != nil) {
        newContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
        [newContext performBlockAndWait:^{
            [newContext setParentContext:masterContext];
        }];
    }

    return newContext;
}

- (void)saveMasterContext {
    [self.masterManagedObjectContext performBlockAndWait:^{
        NSError *error = nil;
        BOOL saved = [self.masterManagedObjectContext save:&error];
        if (!saved) {
            // do some real error handling
            NSLog(@"Could not save master context due to %@", error);
        }
    }];
}

- (void)saveBackgroundContext {
    [self.backgroundManagedObjectContext performBlockAndWait:^{
        NSError *error = nil;
        BOOL saved = [self.backgroundManagedObjectContext save:&error];
        if (!saved) {
            // do some real error handling
            NSLog(@"Could not save background context due to %@", error);
        }
    }];
}

// Returns the managed object model for the application.
// If the model doesn't already exist, it is created from the application's model.
- (NSManagedObjectModel *)managedObjectModel
{
    if (_managedObjectModel != nil) {
        return _managedObjectModel;
    }
    NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"WGTCalculator" withExtension:@"momd"];
    _managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
    return _managedObjectModel;
}

// Returns the persistent store coordinator for the application.
// If the coordinator doesn't already exist, it is created and the application's store added to it.
- (NSPersistentStoreCoordinator *)persistentStoreCoordinator
{
    if (_persistentStoreCoordinator != nil) {
        return _persistentStoreCoordinator;
    }

    NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"WGTCalcul.sqlite"];

    NSError *error = nil;
    _persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
    if (![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error]) {

        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }

    return _persistentStoreCoordinator;
}

#pragma mark - Application's Documents directory

// Returns the URL to the application's Documents directory.
- (NSURL *)applicationDocumentsDirectory
{
    return [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
}


@end

MLVSyncEngine.h
#import <Foundation/Foundation.h>

typedef enum {
    MLVObjectSynced = 0,
    MLVObjectCreated,
    MLVObjectDeleted,
} MLVObjectSyncStatus;

@interface MLVSyncEngine : NSObject
@property (atomic, readonly) BOOL syncInProgress;


+ (MLVSyncEngine *)sharedEngine;

- (void)registerNSManagedObjectClassToSync:(Class)aClass;
- (void)startSync;

@end

MLVSyncEngine.m
#import "MLVSyncEngine.h"

#import "MLVCoreDataController.h"
#import "MLVAFParseAPIClient.h"
#import "AFHTTPRequestOperation.h"
#import "AFJSONRequestOperation.h"

NSString * const kMLVSyncEngineInitialCompleteKey = @"MLVSyncEngineInitialSyncCompleted";
NSString * const kMLVSyncEngineSyncCompletedNotificationName = @"MLVSyncEngineSyncCompleted";

@interface MLVSyncEngine ()
@property (nonatomic, strong) NSMutableArray *registeredClassesToSync;
@property (nonatomic, strong) NSDateFormatter *dateFormatter;

@end

@implementation MLVSyncEngine

@synthesize registeredClassesToSync = _registeredClassesToSync;
@synthesize syncInProgress = _syncInProgress;
@synthesize dateFormatter = _dateFormatter;


+ (MLVSyncEngine *)sharedEngine
{
    static MLVSyncEngine *sharedEngine = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        sharedEngine = [[MLVSyncEngine alloc] init];
    });

    return sharedEngine;
}

- (void)registerNSManagedObjectClassToSync:(Class)aClass
{
    if (!self.registeredClassesToSync) {
        self.registeredClassesToSync = [NSMutableArray array];
    }

    if ([aClass isSubclassOfClass:[NSManagedObject class]]) {
        if (![self.registeredClassesToSync containsObject:NSStringFromClass(aClass)]) {
            [self.registeredClassesToSync addObject:NSStringFromClass(aClass)];
        } else {
            NSLog(@"Unable to register %@ as it is already registered", NSStringFromClass(aClass));
        }
    } else {
        NSLog(@"Unable to reguster %@ as it is not a subclass of NSManagedObject", NSStringFromClass(aClass));
    }
}

- (BOOL)initialSyncComplete{
    return [[[NSUserDefaults standardUserDefaults] valueForKey:kMLVSyncEngineInitialCompleteKey] boolValue];
}

- (void)setInitialSyncCompleted{
    [[NSUserDefaults standardUserDefaults] setValue:[NSNumber numberWithBool:YES] forKey:kMLVSyncEngineInitialCompleteKey];
    [[NSUserDefaults standardUserDefaults] synchronize];
}

- (void)executeSyncCompletedOperations {
    dispatch_async(dispatch_get_main_queue(), ^{
        [self setInitialSyncCompleted];

        NSError *error = nil;
        [[MLVCoreDataController sharedInstance] saveBackgroundContext];
        if (error) {
            NSLog(@"Error saving background context after creating objects on server: %@", error);
        }

        [[MLVCoreDataController sharedInstance] saveMasterContext];

        [[NSNotificationCenter defaultCenter]
         postNotificationName:kMLVSyncEngineSyncCompletedNotificationName
         object:nil];
        [self willChangeValueForKey:@"syncInProgress"];
        _syncInProgress = NO;
        [self didChangeValueForKey:@"syncInProgress"];
    });
}

- (void)startSync
{
    if (!self.syncInProgress) {
        [self willChangeValueForKey:@"syncInProgress"];
        _syncInProgress = YES;
        [self didChangeValueForKey:@"syncInProgress"];

        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{[self downloadDataForRegisteredObjects:YES];
        });
    }
}


- (NSDate *)mostRecentUpdatedAtDateForEntityWithName:(NSString *)entityName {
    __block NSDate *date = nil;
    //
    // Create a new fetch request for the specified entity
    //
    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:entityName];
    //
    // Set the sort descriptors on the request to sort by updatedAt in descending order
    //
    [request setSortDescriptors:[NSArray arrayWithObject:
                                 [NSSortDescriptor sortDescriptorWithKey:@"updatedAt" ascending:NO]]];
    //
    // You are only interested in 1 result so limit the request to 1
    //
    [request setFetchLimit:1];
    [[[MLVCoreDataController sharedInstance] backgroundManagedObjectContext] performBlockAndWait:^{
        NSError *error = nil;
        NSArray *results = [[[MLVCoreDataController sharedInstance] backgroundManagedObjectContext] executeFetchRequest:request error:&error];
        if ([results lastObject])   {
            //
            // Set date to the fetched result
            //
            date = [[results lastObject] valueForKey:@"updatedAt"];
        }
    }];

    return date;
}

- (void)newManagedObjectWithClassName:(NSString *)className forRecord:(NSDictionary *)record {
    NSManagedObject *newManagedObject = [NSEntityDescription insertNewObjectForEntityForName:className inManagedObjectContext:[[MLVCoreDataController sharedInstance] backgroundManagedObjectContext]];
    [record enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {
        [self setValue:obj forKey:key forManagedObject:newManagedObject];
    }];
    [record setValue:[NSNumber numberWithInt:MLVObjectSynced] forKey:@"syncStatus"];
}

- (void)updateManagedObject:(NSManagedObject *)managedObject withRecord:(NSDictionary *)record {
    [record enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {
        [self setValue:obj forKey:key forManagedObject:managedObject];
    }];
}


- (void)setValue:(id)value forKey:(NSString *)key forManagedObject:(NSManagedObject *)managedObject {
    if ([key isEqualToString:@"createdAt"] || [key isEqualToString:@"updatedAt"]) {
        NSDate *date = [self dateUsingStringFromAPI:value];
        [managedObject setValue:date forKey:key];
    } else if ([value isKindOfClass:[NSDictionary class]]) {
        if ([value objectForKey:@"__type"]) {
            NSString *dataType = [value objectForKey:@"__type"];
            if ([dataType isEqualToString:@"Date"]) {
                NSString *dateString = [value objectForKey:@"iso"];
                NSDate *date = [self dateUsingStringFromAPI:dateString];
                [managedObject setValue:date forKey:key];
            } else if ([dataType isEqualToString:@"File"]) {
                NSString *urlString = [value objectForKey:@"url"];
                NSURL *url = [NSURL URLWithString:urlString];
                NSURLRequest *request = [NSURLRequest requestWithURL:url];
                NSURLResponse *response = nil;
                NSError *error = nil;
                NSData *dataResponse = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];
                [managedObject setValue:dataResponse forKey:key];
            } else {
                NSLog(@"Unknown Data Type Received");
                [managedObject setValue:nil forKey:key];
            }
        }
    } else {
        [managedObject setValue:value forKey:key];
    }
}

- (NSArray *)managedObjectsForClass:(NSString *)className withSyncStatus:(MLVObjectSyncStatus)syncStatus {
    __block NSArray *results = nil;
    NSManagedObjectContext *managedObjectContext = [[MLVCoreDataController sharedInstance] backgroundManagedObjectContext];
    NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:className];
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"syncStatus = %d", syncStatus];
    [fetchRequest setPredicate:predicate];
    [managedObjectContext performBlockAndWait:^{
        NSError *error = nil;
        results = [managedObjectContext executeFetchRequest:fetchRequest error:&error];
    }];

    return results;
}

- (NSArray *)managedObjectsForClass:(NSString *)className sortedByKey:(NSString *)key usingArrayOfIds:(NSArray *)idArray inArrayOfIds:(BOOL)inIds {
    __block NSArray *results = nil;
    NSManagedObjectContext *managedObjectContext = [[MLVCoreDataController sharedInstance] backgroundManagedObjectContext];
    NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:className];
    NSPredicate *predicate;
    if (inIds) {
        predicate = [NSPredicate predicateWithFormat:@"objectId IN %@", idArray];
    } else {
        predicate = [NSPredicate predicateWithFormat:@"NOT (objectId IN %@)", idArray];
    }

    [fetchRequest setPredicate:predicate];
    [fetchRequest setSortDescriptors:[NSArray arrayWithObject:
                                      [NSSortDescriptor sortDescriptorWithKey:@"objectId" ascending:YES]]];
    [managedObjectContext performBlockAndWait:^{
        NSError *error = nil;
        results = [managedObjectContext executeFetchRequest:fetchRequest error:&error];
    }];

    return results;
}


- (void)downloadDataForRegisteredObjects:(BOOL)useUpdatedAtDate {
    NSMutableArray *operations = [NSMutableArray array];

    for (NSString *className in self.registeredClassesToSync) {
        NSDate *mostRecentUpdatedDate = nil;
        if (useUpdatedAtDate) {
            mostRecentUpdatedDate = [self mostRecentUpdatedAtDateForEntityWithName:className];
        }
        NSMutableURLRequest *request = [[MLVAFParseAPIClient sharedClient]
                                        GETRequestForAllRecordsOfClass:className
                                        updatedAfterDate:mostRecentUpdatedDate];
        AFHTTPRequestOperation *operation = [[MLVAFParseAPIClient sharedClient] HTTPRequestOperationWithRequest:request success:^(AFHTTPRequestOperation *operation, id responseObject) {
            if ([responseObject isKindOfClass:[NSDictionary class]]) {
            [self writeJSONResponse:responseObject toDiskForClassWithName:className];
                NSLog(@"Response for %@: %@", className, responseObject);

            }
        } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
            NSLog(@"Request for class %@ failed with error: %@", className, error);
        }];

        [operations addObject:operation];
    }

    [[MLVAFParseAPIClient sharedClient] enqueueBatchOfHTTPRequestOperations:operations progressBlock:^(NSUInteger numberOfCompletedOperations, NSUInteger totalNumberOfOperations) {

    } completionBlock:^(NSArray *operations) {
        NSLog(@"All operations completed");

[self processJSONDataRecordsIntoCoreData];
    }];
}

- (void)processJSONDataRecordsIntoCoreData {
    NSManagedObjectContext *managedObjectContext = [[MLVCoreDataController sharedInstance] backgroundManagedObjectContext];
    //
    // Iterate over all registered classes to sync
    //
    for (NSString *className in self.registeredClassesToSync) {
        if (![self initialSyncComplete]) {
            NSDictionary *JSONDictionary = [self JSONDictionaryForClassWithName:className];
            NSArray *records = [JSONDictionary objectForKey:@"results"];
            for (NSDictionary *record in records) {
                [self newManagedObjectWithClassName:className forRecord:record];
            }
        } else {

            NSArray *downloadedRecords = [self JSONDataRecordsForClass:className sortedByKey:@"objectId"];
            if ([downloadedRecords lastObject]) {

                NSArray *storedRecords = [self managedObjectsForClass:className sortedByKey:@"objectId" usingArrayOfIds:[downloadedRecords valueForKey:@"objectId"] inArrayOfIds:YES];
                int currentIndex = 0;

                for (NSDictionary *record in downloadedRecords) {
                    NSManagedObject *storedManagedObject = nil;

                    if ([storedRecords count] > currentIndex) {
                        storedManagedObject = [storedRecords objectAtIndex:currentIndex];
                    }

                    if ([[storedManagedObject valueForKey:@"objectId"] isEqualToString:[record valueForKey:@"objectId"]]) {

                        [self updateManagedObject:[storedRecords objectAtIndex:currentIndex] withRecord:record];
                    } else {

                        [self newManagedObjectWithClassName:className forRecord:record];
                    }
                    currentIndex++;
                }
            }
        }

        [managedObjectContext performBlockAndWait:^{
            NSError *error = nil;
            if (![managedObjectContext save:&error]) {
                NSLog(@"Unable to save context for class %@", className);
            }
        }];


        [self deleteJSONDataRecordsForClassWithName:className];
        [self executeSyncCompletedOperations];
    }
}



- (void)initializeDateFormatter {
    if (!self.dateFormatter) {
        self.dateFormatter = [[NSDateFormatter alloc] init];
        [self.dateFormatter setDateFormat:@"yyyy-MM-dd'T'HH:mm:ss'Z'"];
        [self.dateFormatter setTimeZone:[NSTimeZone timeZoneWithName:@"GMT"]];
    }
}

- (NSDate *)dateUsingStringFromAPI:(NSString *)dateString {
    [self initializeDateFormatter];
    dateString = [dateString substringWithRange:NSMakeRange(0, [dateString length]-5)];

    return [self.dateFormatter dateFromString:dateString];
}

- (NSString *)dateStringForAPIUsingDate:(NSDate *)date {
    [self initializeDateFormatter];
    NSString *dateString = [self.dateFormatter stringFromDate:date];
    dateString = [dateString substringWithRange:NSMakeRange(0, [dateString length]-1)];
    dateString = [dateString stringByAppendingFormat:@".000Z"];

    return dateString;
}

#pragma mark - File Management

- (NSURL *)applicationCacheDirectory
{
    return [[[NSFileManager defaultManager] URLsForDirectory:NSCachesDirectory inDomains:NSUserDomainMask] lastObject];
}

- (NSURL *)JSONDataRecordsDirectory{

    NSFileManager *fileManager = [NSFileManager defaultManager];
    NSURL *url = [NSURL URLWithString:@"JSONRecords/" relativeToURL:[self applicationCacheDirectory]];
    NSError *error = nil;
    if (![fileManager fileExistsAtPath:[url path]]) {
        [fileManager createDirectoryAtPath:[url path] withIntermediateDirectories:YES attributes:nil error:&error];
    }
    return url;
}



-(void)writeJSONResponse:(id)response toDiskForClassWithName:(NSString *)className{
    NSURL *fileURL = [NSURL URLWithString:className relativeToURL:[self JSONDataRecordsDirectory]] ;
    if (![(NSDictionary *)response writeToFile:[fileURL path] atomically:YES]) {
        NSLog(@"Error saving response to disk, will attempt to remove NSNull values and try again.");
        //remove NSNulls and try again...
        NSArray *records = [response objectForKey:@"results"];
        NSMutableArray *nullFreeRecords = [NSMutableArray array];
        for (NSDictionary *record in records) {
            NSMutableDictionary *nullFreeRecord = [NSMutableDictionary dictionaryWithDictionary:record];
            [record enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {
                if ([obj isKindOfClass:[NSNull class]]) {
                    [nullFreeRecord setValue:nil forKey:key];
                }
            }];
            [nullFreeRecords addObject:nullFreeRecord];
        }

        NSDictionary *nullFreeDictionary = [NSDictionary dictionaryWithObject:nullFreeRecords forKey:@"results"];

        if (![nullFreeDictionary writeToFile:[fileURL path] atomically:YES]) {
            NSLog(@"Failed all attempts to save response to disk: %@", response);
        }
    }
}

- (void)deleteJSONDataRecordsForClassWithName:(NSString *)className {
    NSURL *url = [NSURL URLWithString:className relativeToURL:[self JSONDataRecordsDirectory]];

                  NSError *error = nil;
                  BOOL deleted = [[NSFileManager defaultManager] removeItemAtURL:url error:&error];
                  if (!deleted) {
                      NSLog(@"Unable to delete JSON records at %@, reason %@", url, error);
                  }

}

- (NSDictionary *)JSONDictionaryForClassWithName:(NSString *)className {
    NSURL *fileURL = [NSURL URLWithString:className relativeToURL:[self JSONDataRecordsDirectory]];

    return [NSDictionary dictionaryWithContentsOfURL:fileURL];
}

- (NSArray *)JSONDataRecordsForClass:(NSString *)className sortedByKey:(NSString *)key {
    NSDictionary *JSONDictionary = [self JSONDictionaryForClassWithName:className];
    NSArray *records = [JSONDictionary objectForKey:@"results"];
    return [records sortedArrayUsingDescriptors:[NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:key ascending:YES]]];
}
@end

最佳答案

老实说,如果您的数据模型如此简单,并且您在每次加载时都删除了本地持久存储/缓存,那么不使用 Core Data 可能会好得多。

通过根据需要加载数据来保持简单。使用 NSCoding 保存缓存,最初作为占位符加载,而应用程序等待下载新信息。

关于iphone - 使用 Parse 同步数据,而不是下载数据,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/18456166/

相关文章:

ios - iOS 9 内容拦截器是否适用于 UIWebView?

ios - UICollectionView 和 UICollectionViewCell 无法正常工作

objective-c - 为什么我的数据可以成功写入 iPhone 模拟器上的文件,而不是我的设备?

ios - 具有 cocoa touch 的自定义 UI 元素

objective-c - 是否可以在子类中重新声明私有(private) ivar 以使其可访问?

ios - 出现键盘时向上移动 View

iphone - UITableView 节标题和节页脚未更新(重绘问题)

iphone - 在导航栏下添加搜索栏?

ios - NSJSONSerialization解析数据问题

ios - 如何使用导航 Controller 快速重用 View Controller 对象