单例的完整写法

iOS

#pragma mark - singleton

static EmailLoginController *sharedInstance = nil;

+ (EmailLoginController*)sharedInstance {

@synchronized (self) {

if (!sharedInstance) {

sharedInstance = [[EmailLoginController alloc] init];

}

}

return sharedInstance;

}

+ (id)allocWithZone:(struct _NSZone *)zone {

@synchronized (self) {

if (!sharedInstance) {

sharedInstance = [super allocWithZone:zone];

}

}

return sharedInstance;

}

- (id)copyWithZone:(NSZone *)zone {

return sharedInstance;

}