單例模式

單例模式在項目中用的比較多主要用于數據的存儲和使用；

單例設計模式有兩種寫法，第一種是不考慮線程安全的懶漢模式，第二種是考慮線程安全的“餓漢模式”，餓漢模式相對于懶漢模式來說是考慮線程安全，懶漢模式是典型的時間換空間，也就是每次獲取實例都會進行判斷，看是否需要創建實例，浪費判斷的時間。

餓漢模式：當類加載到OC運行時環境中（內存），就會調用+ (void)load一次（一個類只會加載1次）

懶漢模式：每調用一次就會加載；

iOS4之后項目中使用餓漢模式較多

項目中常用到主要有五種類型的數據 NSNumber，NSMutableDictionary，NSString，BOOL，NSInteger

#define USE_INFO [Singleton shareInstance]#import <Foundation/Foundation.h>@interface Singleton : NSObject@PRoperty (atomic, strong) NSNumber *logined;@property (atomic) NSInteger timeOut;@property (nonatomic, retain) NSMutableDictionary *userItems;@property (atomic, assign) BOOL isEle;@property (nonatomic, strong) NSString *username;//單例實例化+ (instancetype)shareInstance;@end

#import "Singleton.h"static Singleton *bankUser = nil;@implementation Singleton#pragma mark - init with singleton//餓漢模式//+ (instancetype)shareInstance//{////    static Singleton *bankUser = nil;//    static dispatch_once_t onceToken;//    //    dispatch_once(&onceToken, ^{//        bankUser = [[Singleton alloc]init];//        bankUser -> _userItems = [NSMutableDictionary dictionary];//        bankUser -> _timeOut = 0;//        bankUser -> _logined = [NSNumber numberWithBool:NO];//        bankUser -> _username = @"";//        bankUser -> _isEle = NO;////    });//    //    return bankUser;//}/*懶漢模式*/+ (instancetype)shareInstance{    @synchronized (self)    {        if (bankUser == nil)            {                bankUser = [[self alloc] init];                bankUser -> _userItems = [NSMutableDictionary dictionary];            }       }        return bankUser;}@end

調用取值如下：

  USE_INFO.username = @"ssdddf";    USE_INFO.logined = @1;    [USE_INFO.userItems setObject:@"usernumber" forKey:@"usernumber"];    USE_INFO.isEle = YES;    USE_INFO.timeOut = 1;    NSLog(@"username==%@ logined==%@userItems==%@isEle=%dtimeOut==%ld",USE_INFO.username,USE_INFO.logined,[USE_INFO.userItems objectForKey:@"usernumber"],!USE_INFO.isEle,(long)USE_INFO.timeOut);