需要帮助使用单例实现 initWithCoder 和 NSUnarchiver

Question

我无法弄清楚如何在 iOS 5 应用程序中进行存档。我有一个单例 SessionStore，如果它在初始化时存在，我想检索 plist 数据。 SessionStore继承自NSObject，有一个ivar，一个NSMutableArray *allSessions，我想从plist文件中加载它。这是 SessionStore.m 不确定问题是否明显或者您是否需要更多信息...谢谢！ Nathan

#import "SessionStore.h"

static SessionStore *defaultStore = nil;

@implementation SessionStore

+(SessionStore *)defaultStore {
    if (!defaultStore) {
        // Load data.plist if it exists
        NSString *pathInDocuments = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent:@"data.plist"];
    NSFileManager *fileManager = [[NSFileManager alloc] init];
    if ([fileManager fileExistsAtPath:pathInDocuments])
        defaultStore = [NSKeyedUnarchiver unarchiveObjectWithFile:pathInDocuments];   
    } else
        defaultStore = [[super allocWithZone:NULL] init]; 

    return defaultStore;
}


+(id)allocWithZone:(NSZone *)zone {
    return [self defaultStore];
}

-(id)init {
    if (defaultStore)
        return defaultStore;

    self = [super init];

    if (self)
        allSessions = [[NSMutableArray alloc] init];

    return self;
}

-(NSMutableArray *)allSessions {
    if (!allSessions) allSessions = [[NSMutableArray alloc] init];
    return allSessions;
}

-(void)setAllSessions:(NSMutableArray *)sessions {
    allSessions = sessions;
}

-(void)encodeWithCoder:(NSCoder *)aCoder {
    [aCoder encodeObject:allSessions forKey:@"All Sessions"];
}

-(id)initWithCoder:(NSCoder *)aDecoder {
    self = [SessionStore defaultStore];
    [self setAllSessions:[aDecoder decodeObjectForKey:@"All Sessions"]];
    return self;
}

在 AppDelegate.m 中，它在终止时保存 plist 文件：

- (void)applicationWillTerminate:(UIApplication *)application
{
    // Save data to plist file
    NSString *pathInDocuments = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent:@"data.plist"];

    [NSKeyedArchiver archiveRootObject:[SessionStore defaultStore] toFile:pathInDocuments];
}

Answer 1

我通常这样做的方法是拥有一个数据文件，在需要时将数据保存到其中，然后在对象初始化时将它们加载回来。就像这样：

@interface SessionStore
@property (nonatomic, copy) NSMutableArray *allSessions;

- (void)loadData;
- (void)saveData;
@end

static SessionStore *sharedInstance = nil;

static NSString *const kDataFilename = @"data.plist";

@implementation SessionStore

@synthesize allSessions = _allSessions;

#pragma mark -

+ (id)sharedInstance {
    if (sharedInstance == nil)
        sharedInstance = [[self alloc] init];
    return sharedInstance;
}


#pragma mark -

- (id)init {
    if ((self = [super init])) {
        [self loadData];
    }
    return self;
}


#pragma mark -

- (void)loadData {
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSString *path = [documentsDirectory stringByAppendingPathComponent:kDataFilename];

    NSFileManager *fileManager = [NSFileManager defaultManager];
    if ([fileManager fileExistsAtPath:path]) {
        NSMutableData *theData = [NSData dataWithContentsOfFile:path];
        NSKeyedUnarchiver *decoder = [[NSKeyedUnarchiver alloc] initForReadingWithData:theData];
        self.allSessions = [[decoder decodeObjectForKey:@"allSessions"] mutableCopy];
        [decoder finishDecoding];
    }

    if (!_allSessions) {
        self.allSessions = [[NSMutableArray alloc] initWithCapacity:0];
    }
}

- (void)saveData {
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSString *path = [documentsDirectory stringByAppendingPathComponent:kDataFilename];

    NSMutableData *theData = [NSMutableData data];
    NSKeyedArchiver *encoder = [[NSKeyedArchiver alloc] initForWritingWithMutableData:theData];

    [encoder encodeObject:_allSessions forKey:@"allSessions"];
    [encoder finishEncoding];

    [theData writeToFile:path atomically:YES];
}

然后，每当我愿意时，我都会调用 saveData 将数据保存回磁盘。这可能是每次 allSessions 发生变化，或者只是在应用程序终止/进入后台时发生一次。这取决于 allSessions 更改的频率以及确保保存数据的重要性。

请记住，单例的代码绝不是最好的 - 如果您担心 sharedInstancedispatch_once 或类似内容背后的推理。代码> 很花哨。

我认为这比你的方法更好，因为你试图序列化整个单例对象而不仅仅是它的内容，我认为这更容易理解正在发生的事情，然后单例本身处理所有加载和保存，而不是让你的NSKeyedArchiver 像您所做的那样溢出到应用程序委托中。