iOS:单例返回null

我有一个单例，我将数据传递给它，但它返回null。在我的情况下，你能帮助我吗。提前感谢：）

这是我的密码

卡片.h

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

+(Card *)getCard;

@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;

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;
}

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

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"];
}

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

这是我的测试代码，看看它是否工作

测试.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;
}

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

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"];
}

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

但是这个代码给我（null）

将其替换为此代码

static Card *instance;

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

---

实例对象的类名错误，在singleton方法中，返回的数据类型也错误。我想你会明白我在说什么

在什么帮助下ḯ Sujjesu可以如下修改您的代码，因为 行

静态csCard*实例你正在使用
csCard
我认为这是打字错误，所以你最好这样做



  #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"];
  }



在您使用此共享实例的类中，使用如下所示

  - (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);

   }

像这样修改您的类

卡片.h

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

+(Card *)getCard;

@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;

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;
}

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

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"];
}

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

不需要重写init

在你的测试课上

它应该是work
Ok。现在在测试类中，您在哪个位置编写代码（例如：单击按钮）？我认为你正在用任何一种视图循环方法编写测试类的代码，即在viewDidLoad或ViewWillDisplay上，原因是当时textfield值将为null，因为用户没有输入值。谢谢！这么强是我唯一的问题：）顺便说一句，感谢setter和getter方法提示，它真的很有用：D+100000