Three ways Swift defines a single case

The first type: Use GCD. Customize a class to inherit the classes you want to inherit, define a static optional variable, declare a dispatch_once_t, and assign an initial value of 0 (0 means it has not been instantiated, if the instance is over its value is always 1), the remainder is similar to the OC definition Singleton

1 classNetworktools:afhttpsessionmanager {2 3     //MARK:-Single case4     Staticvar instance:networktools?5     Staticvar once_t:dispatch_once_t =06     7     classFunc shareinstance ()Networktools8     {9Dispatch_once (&once_t) { Ten              OneInstance =Networktools () A         } -          -         returninstance! the     } -}

The second kind: directly define a static immutable constant, and then define a class method return value for the class you want to Singleton, return this variable directly

1     static Let Networktool = networktools ()2     3     class func Shareinstance () networktools {45         return  networktool  6     }

Third: Similar to the second one, except that defining constants is directly implemented in a lazy-loading manner

1 StaticLet Networktool:networktools = {2        3Let Networktool = Networktools (BaseURL:NSURL.init (string:"https://api.weibo.com/"))4         5NetworkTool.responseSerializer.acceptableContentTypes = (Nsset (objects:"Application/json","Text/json","Text/javascript","Text/plain") as! Set<string>)6 7         returnNetworktool8     }()9     Ten     classFunc shareinstance ()Networktools One     { A         returnNetworktool -}

Three ways Swift defines a single case