在iOS的開發(fā)中，單例設(shè)計(jì)模式（Singleton Pattern）是用得最多的設(shè)計(jì)模式之一了。在iOS的SDK中，很多地方都可以看到它的蹤影。例如UIApplication, 我們可以在任何地方調(diào)用sharedApplication方法來獲取當(dāng)前運(yùn)行的UIApplication實(shí)例。對于這個設(shè)計(jì)模式的優(yōu)缺點(diǎn)我們這里就不討論了，我們著重放在如何實(shí)現(xiàn)。

文章用到的Demo源碼在這里.

Objective-C

在ARC模式下，我們創(chuàng)建一個單例類InfoManager

//InfoManager.h
#import <Foundation/Foundation.h>

NS_ASSUME_NONNULL_BEGIN

@interface InfoManager : NSObject

+(instancetype)shareInstance;

@end

NS_ASSUME_NONNULL_END

//InfoManager.m
#import "InfoManager.h"

static InfoManager *_infoManager = nil;

@implementation InfoManager

+(instancetype)shareInstance{
    
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _infoManager = [[self alloc] init];
    });
    
    return _infoManager;
}

+(instancetype)allocWithZone:(struct _NSZone *)zone{
    
    @synchronized (_infoManager) {
        if (_infoManager == nil) {
            _infoManager = [super allocWithZone:zone];
        }
    }
    return _infoManager;
}

-(instancetype)init{
    
    @synchronized (self) {
        self = [super init];
    }
    
    return self;
}

@end

在NON-ARC模式下，在實(shí)現(xiàn)文件要重寫其他的方法

//InfoManager.m
#import "InfoManager-NonARC.h"

static InfoManager_NonARC *_infoManager = nil;

@implementation InfoManager_NonARC

+(instancetype)shareInstance{
    
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _infoManager = [[self alloc] init];
    });
    
    return _infoManager;
}

+(instancetype)allocWithZone:(struct _NSZone *)zone{
    
    @synchronized (_infoManager) {
        if (_infoManager == nil) {
            _infoManager = [super allocWithZone:zone];
        }
    }
    return _infoManager;
}

-(instancetype)init{
    
    @synchronized (self) {
        self = [super init];
    }
    
    return self;
}

-(instancetype)retain{
    return self;
}

-(NSUInteger)retainCount{
    return UINT_MAX;
}

-(oneway void)release{
    
}

-(instancetype)autorelease{
    return self;
}

@end

如果要給某個類關(guān)閉ARC，如圖在TARGETS -> Build Phases -> Compile Sources 里給相應(yīng)的class加 -fno-objc-arc

WX20180904-143419@2x.png

如何在Swift下創(chuàng)建一個單例

//  LocationManager.swift
import UIKit

class LocationManager: NSObject {
    
    static let shared = LocationManager()
    
    var hasLocation: Bool?
    
    private override init() {
        
    }
    
    func requestForLocation(){

        hasLocation = true
        print("Location granted")
    }

}

我們創(chuàng)建這個單例實(shí)例的話代碼如下

LocationManager.shared.requestForLocation()

如果嘗試使用init的方法就會報(bào)錯

WX20180904-144831@2x.png