iOS设计模式

iOS设计模式 - 单例

原理图

源码

https://github.com/YouXianMing/iOS-Design-Patterns

//
//  Singleton.h
//  SingletonPattern
//
//  Created by YouXianMing on 15/8/6.
//  Copyright (c) 2015年 YouXianMing. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface Singleton : NSObject

+ (Singleton *)sharedInstance;

@end

//
//  Singleton.m
//  SingletonPattern
//
//  Created by YouXianMing on 15/8/6.
//  Copyright (c) 2015年 YouXianMing. All rights reserved.
//

#import "Singleton.h"

static Singleton *_sharedSingleton = nil;

@implementation Singleton

- (instancetype)init {
    
    [NSException raise:@"SingletonPattern"
                format:@"Cannot instantiate singleton using init method, sharedInstance must be used."];
    
    return nil;
}

- (id)copyWithZone:(NSZone *)zone {

    [NSException raise:@"SingletonPattern"
                format:@"Cannot copy singleton using copy method, sharedInstance must be used."];
    
    return nil;
}

+ (Singleton *)sharedInstance {

    if (self != [Singleton class]) {
        
        [NSException raise:@"SingletonPattern"
                    format:@"Cannot use sharedInstance method from subclass."];
    }
    
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        
        _sharedSingleton = [[Singleton alloc] initInstance];
    });

    return _sharedSingleton;
}

#pragma mark - private method

- (id)initInstance {

    return [super init];
}

@end