Swift 利用类名动态创建实例对象

OC 通过字符串创建实例对象

在OC中我们可以通过下列方法轻松创建实例对象

NSString *className = @"UIView";
Class class = NSClassFromString(className);
UIView *view = [[class alloc] init];

Swift 中通过字符串创建实例对象

1. 获取命名空间

   func currentNameSpace() -> String? {
        guard let spaceName = Bundle.main.infoDictionary!["CFBundleExecutable"] as? String else {
            print("获取命名空间失败")
            return nil
        }
        return spaceName
    }
   

2. 获取类名并创建实例对象

   func registerAdapters<T>() -> [T]? where T: Adapter {
        guard let spaceName = currentNameSpace() else {
            return nil
        }
        var adapters: [T] = []
        for adapter in adaptersName {
            let fullName = spaceName + "." + adapter
            guard let metaClass = NSClassFromString(fullName) as? T.Type else {
                print("获取元类型失败")
                continue
            }
   
            adapters.append(metaClass.init(name: adapter))
        }
        return adapters
    }
   

   通过 NSClassFromString 获取到的元类型需要转成确定的类型，这里使用了范型 T: Adapter。 Adapter 为声明的协议。

   protocol Adapter {
    init(name: String)
    func showing()
   }
   

3. 失败的尝试

   • 首先声明 3 个遵循 Adapter 协议的类

     • 注意：因为Adapter协议中声明了 init(name: String) 方法，所以实现init方法时，要加 required 关键字，代表其子类也要实现此 init 方法。
     • DESIGNATED，CONVENIENCE 和 REQUIRED

       class FirstAdapter: Adapter {
           var name: String!
           required init(name: String) {
               super.init(name: name)
               self.name = name
               print(name + " is loading")
           }
       
           func showing() {
               print(name + " is showing")
           }
       }
       
       class SecondAdapter: Adapter {
           var name: String!
           required init(name: String) {
               super.init(name: name)
               self.name = name
               print(name + " is loading")
           }
       
           func showing() {
               print(name + " is showing")
           }
       }
       
       class ThirdAdapter: Adapter {
           var name: String!
           required init(name: String) {
               super.init(name: name)
               self.name = name
               print(name + " is loading")
           }
       
           func showing() {
               print(name + " is showing")
           }
       }
       

   • demo 报错信息
     报错信息 Generic parameter 'T' could not be inferred 不能推导出范型的具体类型。

4. 做的改进

   • 声明一个 FatherAdapter 类，遵循 Adapter 协议

     class FatherAdapter: Adapter {
     required init(name: String) {}
     
     func showing() {}
     }
     

   • FirstAdapter, SecondAdapter, ThirdAdapter 都继承 FatherAdapter
     • 添加 super.init(name: name)
     • showing() 添加 override

    class FirstAdapter: FatherAdapter {
        var name: String!
        required init(name: String) {
            super.init(name: name)
            self.name = name
            print(name + " is loading")
        }
   
        override func showing() {
            print(name + " is showing")
        }
    }
   
    class SecondAdapter: FatherAdapter {
        var name: String!
        required init(name: String) {
            super.init(name: name)
            self.name = name
            print(name + " is loading")
        }
   
        override func showing() {
            print(name + " is showing")
        }
    }
   
    class ThirdAdapter: FatherAdapter {
        var name: String!
        required init(name: String) {
            super.init(name: name)
            self.name = name
            print(name + " is loading")
        }
   
        override func showing() {
            print(name + " is showing")
        }
    }
   

   • 改进 demo
     • let adapters: [FatherAdapter] = register.registerAdapters() 范型直接使用 FaterAdapter

   class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = UIColor.blue
   
        let register = Register(adaptersName: ["FirstAdapter", "SecondAdapter", "ThirdAdapter"])
        guard let adapters: [FatherAdapter] = register.registerAdapters() else {
            return
        }
        guard adapters.count > 0 else {
            return
        }
        for adapter in adapters {
            adapter.showing()
        }
    }
   }
   

   • 运行结果