用GCD实现单例模式的步骤：
步骤1. 创建头文件 XZSingleton.h，里面代码如下：
// .h文件 #define XZSingletonH(name) + (instancetype)shared##name; // .m文件 #if __has_feature(objc_arc) #define XZSingletonM(name) \ static id _instace; \ \ + (id)allocWithZone:(struct _NSZone *)zone \ { \ static dispatch_once_t onceToken; \ dispatch_once(&onceToken, ^{ \ _instace = [super allocWithZone:zone]; \ }); \ return _instace; \ } \ \ + (instancetype)shared##name \ { \ static dispatch_once_t onceToken; \ dispatch_once(&onceToken, ^{ \ _instace = [[self alloc] init]; \ }); \ return _instace; \ } \ \ - (id)copyWithZone:(NSZone *)zone \ { \ return _instace; \ } #else #define XZSingletonM(name) \ static id _instace; \ \ + (id)allocWithZone:(struct _NSZone *)zone \ { \ static dispatch_once_t onceToken; \ dispatch_once(&onceToken, ^{ \ _instace = [super allocWithZone:zone]; \ }); \ return _instace; \ } \ \ + (instancetype)shared##name \ { \ static dispatch_once_t onceToken; \ dispatch_once(&onceToken, ^{ \ _instace = [[self alloc] init]; \ }); \ return _instace; \ } \ \ - (id)copyWithZone:(NSZone *)zone \ { \ return _instace; \ } \ \ - (oneway void)release { } \ - (id)retain { return self; } \ - (NSUInteger)retainCount { return 1;} \ - (id)autorelease { return self;} #endif
步骤2. 要实现的单例类，比如 XZDataTool，XZDataTool.h XZDataTool.m代码分别 如下：
#import <Foundation/Foundation.h> @interface XZDataTool : NSObject XZSingletonH(DataTool) @end
#import "XZDataTool.h" @implementation XZDataTool XZSingletonM(DataTool) @end