iOS：Singleton返回null

Question

我有一个单身人士，我将数据传递给它，但它返回null，请你在我的情况下帮助我。在此先感谢：）

这是我的代码

Card.h

@property (weak,nonatomic) NSString *email;
@property (weak,nonatomic) NSString *fName;
@property (weak,nonatomic) NSString *lName;
@property (weak,nonatomic) NSString *category;

+(Card *)getCard;

Card.m

@synthesize email;
@synthesize fName;
@synthesize lName;
@synthesize category;

static csCard *instance;

+(Card *) getCard
{
    @synchronized (self)
    {
        if(instance == nil)
        {
            instance = [[Card alloc]init];
        }
    }
    return instance;
}

- (id) init{

    self.email = [[NSUserDefaults standardUserDefaults]stringForKey:@"email"];
    self.fName = [[NSUserDefaults standardUserDefaults]stringForKey:@"firstName"];
    self.lName = [[NSUserDefaults standardUserDefaults]stringForKey:@"lastName"];
    self.category = @"TestCategory";

    return self;
}

这是我的测试代码，看看它是否正常工作

Test.m

Card *card = [Card getCard];
    [card setEmail:self.emailField.text];
    NSLog(@"%@",card.email);

但是这段代码给了我（null）

Answer 1

像这样修改你的课程。

<强> Card.h

@property (strong,nonatomic) NSString *email; //Let the modal be strong property
@property (strong,nonatomic) NSString *fName;
@property (strong,nonatomic) NSString *lName;
@property (strong,nonatomic) NSString *category;

+(Card *)getCard;

<强> Card.m

static Card *instance;

+(Card *) getCard
{
    @synchronized (self)
    {
        if(instance == nil)
        {
            instance = [[Card alloc]init];
        }
    }
    return instance;
}
- (NSString)email{
return [[NSUserDefaults standardUserDefaults]stringForKey:@"email"];
}

- (void)setEmail:(NSString)email{
[[NSUserDefaults standardUserDefaults] setString:email forkey:@"email"];
}

无需覆盖init

在您的测试类中

Card *card = [Card getCard];
    [card setEmail:self.emailField.text];
    NSLog(@"%@",card.email);

Answer 2

static csCard *instance;

+(csCard *) getCard
{
@synchronized (self)
{
    if(instance == nil)
    {
        instance = [[csCard alloc]init];
    }
}
return instance;
}

将其替换为此代码

static Card *instance;

 +(Card *) getCard
{
@synchronized (self)
{
    if(instance == nil)
    {
        instance = [[Card alloc]init];
    }
}
return instance;
}

实例对象的类名是错误的，在单例方法中，返回数据类型也是错误的。我想你会明白我在说什么。

Answer 3

在βhargavḯsujjested的帮助下，你可以修改你的代码，如下所示 在static csCard *instance;行csCard我正在使用 #import "Card.h" static dispatch_once_t onceDispach; @implementation Card @synthesize email = _email; @synthesize fName; @synthesize lName; @synthesize category; static Card *instance = nil; //change this to Card because this instance which is of type Card +(Card *)getCard { dispatch_once(&onceDispach, ^{ instance = [[self alloc] init];//careate Card shared object named instance }); return instance; } - (id) init { self.email = [[NSUserDefaults standardUserDefaults]stringForKey:@"email"]; self.fName = [[NSUserDefaults standardUserDefaults]stringForKey:@"firstName"]; self.lName = [[NSUserDefaults standardUserDefaults]stringForKey:@"lastName"]; self.category = @"TestCategory"; return self; } @end - (NSString *)email { return _email; } - (void)setEmail:(NSString *)email { _email = email; NSUserDefaults *userDefault = [NSUserDefaults standardUserDefaults]; [userDefault setObject:email forKey:@"email"]; } 我认为这是错误的，所以你可以做得更好，

  - (void)actionMathodCalled
   {
     Card *card = [Card getCard];
     NSLog(@"before saving to defaults->%@",card.email);
     [card setEmail:@"happyCoding@ymail.com"];
     NSLog(@"after savng to defaults->%@",card.email);

   }

在您正在使用此共享实例的类中使用，如下所示

{{1}}

Answer 4

+ (Card *)instance {
    static Card *sharedInstance = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        sharedInstance = [[Card alloc] init];
    });
    return sharedInstance;
}

应该是工作