创建方式一： GCD创建
static id _instance = nil;
+ (instancetype)sharedInstance {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
_instance = [[self alloc] init];
});
return _instance;
}
+ (instancetype)allocWithZone:(struct _NSZone *)zone {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
_instance = [super allocWithZone:zone];
});
return _instance;
}
- (id)copyWithZone:(NSZone *)zone {
return _instance;
}
- (id)mutableCopyWithZone:(NSZone *)zone {
return _instance;
}
创建方式二： 互斥锁创建
static id _instance = nil;
+ (instancetype)allocWithZone:(struct _NSZone *)zone {
@synchronized(self) {
if (_instance == nil) {
_instance = [super allocWithZone:zone];
}
}
return _instance;
}
+ (instancetype)sharedInstance {
@synchronized(self) {
if (_instance == nil) {
_instance = [[self alloc] init];
}
}
return _instance;
}
- (id)copyWithZone:(NSZone *)zone {
return _instance;
}
- 单例创建之后我们还需要将原本的创建初始化方法屏蔽掉
方法一:在.h文件中声明禁止方法
+(instancetype) alloc __attribute__((unavailable("call other method instead")));
-(instancetype) init __attribute__((unavailable("call other method instead")));
+(instancetype) new __attribute__((unavailable("call other method instead")));
方法二：重载init、new
- (instancetype)init {
[self doesNotRecognizeSelector:_cmd];
return nil;
}
// -----或----- //
- (instancetype)init {
return [self.class sharedInstance];
}
//------加------//
- (instancetype)new {
return [self.class sharedInstance];
}
