详解IOS 单例的两种方式

#pragma mark - #pragma mark sharedSingleton methods  //单例函数 static RtDataModel *sharedSingletonManager = nil;  + (RtDataModel *)sharedManager {   @synchronized(self) {     if (sharedSingletonManager == nil) {       sharedSingletonManager = [[self alloc] init];     }   }   return sharedSingletonManager; }  + (id)allocWithZone:(NSZone *)zone {   @synchronized(self) {     if (sharedSingletonManager == nil) {       sharedSingletonManager = [super allocWithZone:zone];       return sharedSingletonManager; // assignment and return on first allocation     }   }   return nil; //on subsequent allocation attempts return nil }  - (id)copyWithZone:(NSZone *)zone {   return sharedSingletonManager; }  - (id)retain {   return sharedSingletonManager; }  - (NSUInteger)retainCount {   return UINT_MAX; //denotes an object that cannot be released }  - (oneway void)release {   //do nothing }  - (id)autorelease {   return sharedSingletonManager; }  //单例函数结束 

#import <Foundation/Foundation.h>  @interface RtTestDataModel : NSObject {   NSMutableArray      * _buyDataTArray;   NSMutableArray      * _sellDataTArray; }  + (RtTestDataModel *)sharedManager;  - (void)addOptionBuyDataArrayModel: (NSMutableArray *)DataArray; - (NSMutableArray *)getOptionBuyDataArrayModel;  @end 

#import "RtTestDataModel.h"  @implementation RtTestDataModel  + (RtTestDataModel *)sharedManager {   static RtTestDataModel *sharedManager = nil;   static dispatch_once_t predicate;      dispatch_once(&predicate,^{     sharedManager = [[RtTestDataModel alloc]init];   });    return sharedManager; }  - (void)dealloc {   [_buyDataTArray removeAllObjects];   [_buyDataTArray release];      [super dealloc]; }  - (id)init {   self = [super init];      if (self != nil) {     _buyDataTArray = [[NSMutableArray alloc] initWithCapacity:8];   }   return self; }  - (void)addOptionBuyDataArrayModel: (NSMutableArray *)DataArray{      if (DataArray != nil) {          [_buyDataTArray removeAllObjects];     [_buyDataTArray addObjectsFromArray:DataArray];   } }  - (NSMutableArray *)getOptionBuyDataArrayModel{      return _buyDataTArray; } @end