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如何在swift中实现监听器模式

design-patterns swift ios

user2930077 · 技术社区 · 6 年前

我是刚从爪哇搬到斯威夫特的。一些设计模式的实现让我困惑。

例如,我有java代码中的presudo模式观察器(回调)(下面有一个示例)。也就是说,UI将自己的侦听器传递给Manager类,侦听回调isConnected和isDisconnected。如果执行回调,UI类将显示某些消息“isConnected”或“isDisconnected”

    public class UI{
        private Manager mManager;
        void createManager(){
            mManager = new Manager(mManagerLister);
        }
        public void showMessage(String aMsg){
            print(aMsg)
        }
        private final IManagerListener mManagerLister = new IManagerListener{
            void isConnected(){
                this.showMessage("isConnected") 
            }
            void isDisconnected(){
                this.showMessage("isConnected")
            }
        }
    }

    public class Manager{
        interface IManagerListener{
            void isConnected();
            void isDisconnected();
        }
        private final mListener; 
        public Manager(IManagerListener aListener){
            mListener = aListener;
        }
    }

如何将此java代码正确地移植到swift代码?我尝试移植但出现错误消息 “UI”类型的值没有成员“showMessage” 显示

  public class UI{
    var manager: Manager?
    var managerListener: IManagerListener?
    func createManager(){
        managerListener = ManagerListenerImp(self)  
        manager = Manager(managerListener)
    }
    public func showMessage(msg: String){
        print(msg)
    }
    class ManagerListenerImp: IManagerListener{
        weak var parent: UI 
        init(parent : UI ){
            self.parent = parent
        }
        func isConnected(){
            parent.showMessage("isConnected") 
            // Value of type 'UI' has no member 'showMessage'
            }
        ..........
    } 
}

也许存在一种更优雅的方法来使用回调,而我的方法不正确?

2 回复 | 直到 6 年前

Sandeep Bhandari 6 年前

有多种方法可以实现这一目标。

委托模式(使用只不过是接口的协议在Java中)
使用块/闭包
使用KVO

因为您使用了接口,所以我将在下面详细介绍委托模式。

按以下方式修改代码

声明协议

@objc protocol ManagerListenerImp {
    func isConnected()
}

在Manager类中声明变量

class Manager {
    weak var delegate : ManagerListenerImp? = nil
}

确认至 ManagerListenerImp 在UI类中

extension UI : ManagerListenerImp {
    func isConnected () {
        //your isConnected implementation here
    }
}

将UI实例(swift中的self和JAVA中的this传递给manager类)

func createManager(){
    manager = Manager()
    manager?.delegate = self
}

最后,只要你想触发 isConnected 从…起 Manager 课堂简单地说

self.delegate?.isConnected()

在你的经理课上

希望有帮助

Arjo Nagelhout 3 年前

我对哪个类引用哪个类有点困惑,但在下面的示例中,这应该不会太难改变。

您可能正在寻找观察者模式。这可以使多个对象侦听相同的更改:

1、ManagerStateListener协议

由应对管理器状态更改作出反应的任何类实现的协议

protocol ManagerStateListener: AnyObject {
    func stateChanged(to state: Manager.State)
}

2、经理类

Manager类包含:

其状态
包含侦听器的列表
用于添加、删除和调用侦听器的方法
实现ManagerStateListener协议的示例类


class Manager {
    
    /// The possible states of the Manager
    enum State {
        case one
        case two
        case three
    }
    
    /// The variable that stores the current state of the manager
    private var _currentState: State = .one
    var currentState: State {
        get {
            return _currentState
        }
        set {
            _currentState = newValue
            
            /// Calls the function that will alert all listeners
            /// that the state has changed
            invoke()
        }
    }
    
    /// The list with all listeners
    var listeners: [ManagerStateListener] = []
    
    /// A specific listener that gets initialised here
    let someListener = SomeListener()
    
    init() {
        addListener(someListener) /// Add the listener to the list
    }
    
    /// Method that invokes the stateChanged method on all listeners
    func invoke() {
        for listener in listeners {
            listener.stateChanged(to: currentState)
        }
    }
    
    /// Method for adding a listener to the list of listeners
    func addListener(_ listener: ManagerStateListener) {
        listeners.append(listener)
    }
    
    /// Method for removing a specific listener from the list of listeners
    func removeListener(_ listener: ManagerStateListener) {
        if let index = listeners.firstIndex(where: { $0 === listener }) {
            listeners.remove(at: index)
        }
    }
}

3、SomeListener类

实现ManagerStateListener协议的示例侦听器,由Manager类持有

class SomeListener : ManagerStateListener {
    
    func stateChanged(to state: Manager.State) {
        /// Do something based on the newly received state
        switch state {
            case .one:
                print("State changed to one")
            case .two:
                print("State changed to two")
            case .three:
                print("State changed to three")
        }
    }
}

我希望这能有所帮助。