Question

* 我肯定需要休息一下......原因很简单 - 数组没有分配...感谢您的帮助。由于这个令人尴尬的错误，我标记了我的帖子以删除它。我觉得它对用户没用;）*

我刚尝试在iOS中创建一个单例类，但我可能犯了一个错误。代码（无需ARC）：

#import "PeopleDatabase.h"
#import "Person.h"

#import <Foundation/Foundation.h>

@interface PeopleDatabase : NSObject{objetive
    NSMutableArray* _arrayOfPeople;
}

+(PeopleDatabase *) getInstance;

@property (nonatomic, retain) NSMutableArray* arrayOfPeople;


@end

-

    @implementation PeopleDatabase
    @synthesize arrayOfPeople = _arrayOfPeople;

    static PeopleDatabase* instance = nil;

    -(id)init{
        if(self = [super init]) {
            Person* person = [[[Person alloc] initWithName:@"John" sname:@"Derovsky" descr:@"Some kind of description" iconName:@"johnphoto.png" title:Prof] retain];

            [_arrayOfPeople addObject:person];
            NSLog(@"array count = %d", [_arrayOfPeople count]); // <== array count = 0 
            [person release];
        }
        return self;
    }

    +(PeopleDatabase *)getInstance {
        @synchronized(self)
        {
            if (instance == nil)
                NSLog(@"initializing");
                instance = [[[self alloc] init] retain];
                NSLog(@"Address: %p", instance);
        }
        return(instance);
    }

    -(void)dealloc {

        [instance release];
        [super dealloc];
    }
@end

像这里一样调用getInstance：

PeopleDatabase *database = [PeopleDatabase getInstance];
NSLog(@"Adress 2: %p", database);

地址2的值与getInstance中的值相同。

Answer 1

创建单身的标准方法就像......

Singleton.h

@interface MySingleton : NSObject

+ (MySingleton*)sharedInstance;

@end

Singleton.m

#import "MySingleton.h"

@implementation MySingleton

#pragma mark - singleton method

+ (MySingleton*)sharedInstance
{
    static dispatch_once_t predicate = 0;
    __strong static id sharedObject = nil;
    //static id sharedObject = nil;  //if you're not using ARC
    dispatch_once(&predicate, ^{
        sharedObject = [[self alloc] init];
        //sharedObject = [[[self alloc] init] retain]; // if you're not using ARC
    });
    return sharedObject;
}

@end

Answer 2

检查此Apple doc如何创建单例实例：

https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/CocoaFundamentals/CocoaObjects/CocoaObjects.html

Answer 3

    @synchronized(self)
    {
        if (instance == nil)
            NSLog(@"initializing");
            instance = [[[self alloc] init] retain];
            NSLog(@"Address: %p", instance);
    }

您似乎错过了if声明的大括号。如上所述，当instance == nil发出日志消息时，您唯一做的就是不同。

Answer 4

在网络阅读和个人练习之后，我目前的单身实施是：

@interface MySingleton

@property myProperty;
+(instancetype) sharedInstance;

@end


@implementation MySingleton

+ (instancetype) sharedInstance
{
    static dispatch_once_t pred= 0;
    __strong static MySingleton *singletonObj = nil;
    dispatch_once (&pred, ^{
        singletonObj = [[super allocWithZone:NULL]init];
        singletonObj.myProperty = initialize ;
    });

    return singletonObj;
}

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

-(id)copyWithZone:(NSZone *)zone
{
    return self;
}

这是一个线程安全的实现，通过调用＆＃34; alloc init＆＃34;来避免创建新对象的风险。在你的班上属性初始化必须在块内部进行，而不是在＆＃34; init＆＃34;内部进行。因类似原因而改写。

Answer 5

在这个函数中+(PeopleDatabase *)getInstance我认为你需要正确放置花括号：像这样

+(PeopleDatabase *)getInstance {
    @synchronized(self)
    {
        if (instance == nil)
        {
            NSLog(@"initializing");
            instance = [[[self alloc] init] retain];
            NSLog(@"Address: %p", instance);
        }
        return instance ;
    }
}

Answer 6

这是一个错误，可以通过一些解压缩的约定来避免，它总是使用大括号后跟if和else。

+(PeopleDatabase *)getInstance {
    @synchronized(self)
    {
        if (instance == nil)
            NSLog(@"initializing");
            instance = [[[self alloc] init] retain];
            NSLog(@"Address: %p", instance);
    }
    return(instance);
}

如果instance为nil则为下一个语句，只执行该语句。这就是nslog而不是分配。然后无论如何都要分配实例，无论之前是否使用过。这将为您在每次通话时提供新的单身人士。 BTW导致泄漏。

+(PeopleDatabase *)getInstance {
    @synchronized(self)
    {
        if (instance == nil) {
            NSLog(@"initializing");
            instance = [[[self alloc] init] retain];
            NSLog(@"Address: %p", instance);
        }
    }
    return(instance);
}

但是这个错误在调试时出现了。它可能会让您感到困惑，但无法解决原始问题。请添加一个alloc和init，并保留_arrayOfPeople。

-(id)init{
    if(self = [super init]) {
        Person* person = [[[Person alloc] initWithName:@"John" sname:@"Derovsky" descr:@"Some kind of description" iconName:@"johnphoto.png" title:Prof] retain];

        _arrayOfPeople = [[[NSMutableArray alloc] init] retain]; //dont forget the release
        [_arrayOfPeople addObject:person];
        NSLog(@"array count = %d", [_arrayOfPeople count]); // <== array count = 1 !!!  
        [person release];
    }
    return self;
}

在你的代码中，_arrayOfPeople为nil，addObject被发送到nil，这不会导致中止但也不会执行任何操作。然后将count发送到nil，返回0 / nil。

Objective C - 示例Singleton实现

6 个答案: