使用单例类的全局变量 NSMuteableArray

问题描述

我在创建一种将集合传递给不同视图控制器的好方法时遇到了麻烦.例如，我创建了一个名为 Message 的自定义类，其中包含一堆属性.我想要一个全局的 NSMutableArray 存储在一个名为消息的全局变量中，我可以添加到任何地方或从任何地方获取.Stackoverflow 上的每个人都说不要使用你的 delagate 类来存储全局变量，所以我创建了一个名为 Shared 的单例类.在那里，我为 NSMutableArray 创建了一个名为 messages 的属性，如下所示:

I'm having trouble creating a nice way of passing a collection around to different view controllers. For example, I created a custom class called Message with a bunch of attributes. I want to have a global NSMutableArray of those stored in a global variable of sorts called messages that I can add to or get from anywhere. Everyone on Stackoverflow says not to use your delagate class to store global variables so I created a singleton class called Shared. In there I created a property for the NSMutableArray called messages like this:

@interface Shared : NSObject {

}

@property (nonatomic, retain) NSMutableArray *messages;

+(Shared *) sharedInstance;

@end

而我的 .h 文件是(重要的部分):

And my .h file is (the important part):

#import "Shared.h"
static Shared* sharedInstance;

@implementation Shared

@synthesize messages;

static Shared *sharedInstance = nil;

-(id) init {
    self = [super init];
    if (self != nil){

    }
    return self;
}

-(void) initializeSharedInstance {

}

+ (Shared *) sharedInstance{
    @synchronized(self) {
        if (sharedInstance == nil){
            sharedInstance = [[self alloc] init];
            [sharedInstance initializeSharedInstance];

        }
        return (sharedInstance);
    }
}

在我的另一个视图控制器中，我首先导入Shared.h"，然后试试这个:

In my other view controller, I first import "Shared.h", then try this:

[[Shared sharedInstance].messages addObject:m];

NSLog([NSString stringWithFormat:@"Shared messages = %@", [Shared sharedInstance].messages]);

它一直打印 null 而不是 m 个对象的集合.有什么想法吗?

It keeps printing null instead of the the collection of m objects. Any thoughts?

推荐答案

你需要有一个静态变量.

You need to have a static variable.

在.h中:

@interface Shared : NSObject
{
    NSMutableArray *messages;
}

@property (nonatomic, retain) NSMutableArray *messages;

+ (Shared*)sharedInstance;

@end

在.m:

static Shared* sharedInstance;

@implementation Shared

@synthesize messages;


+ (Shared*)sharedInstance
{
    if ( !sharedInstance)
    {
        sharedInstance = [[Shared alloc] init];

    }
    return sharedInstance;
}

- (id)init
{
    self = [super init];
    if ( self )
    {
        messages = [[NSMutableArray alloc] init];
    }
    return self;
}

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