背后的故事之快樂的Lambda表達式二

1、背后的故事之-快樂的Lambda表達式（二）Lambda表達式玩轉(zhuǎn)姜態(tài)Lambda如何實現(xiàn)賽態(tài)？我們用抽象類和虛方法了，為什么還要用Lambda這個玩意？且看 下面的代碼：C#class MyBaseClasspublic Action SomeAction get, protected set, public MyBaseClassOSome A chon = 0 =>/Do somethingi,class MyliiheritedClass MyBaseClasspublic MylnhentedClassOSome A chon = 0 => /Do sometlung d

2、ifferent!,class MyBaseClasspublic Action SomeAction get, protected set, public MyBaseClassOSome A chon = 0 =>/Do somethingi;class MylnheritedClass MyBaseClasspublic MylnhmtedClassOSomeAction = 0 => /Do sometliing different!,我們的基類不是抽象類，也沒有虎方法，但是把屬性通過委托的方式暴露出來，然后在子類 中匝新為我們的SomeAction 予一個新的表達式。這就

3、是我們實現(xiàn)多態(tài)的過程，當然父類 中的SomeAction的set fj' protected的保護級別，不然就會被外部隨易修改了。但是這還不 完美，父類的SomeAction在子類中被覆蓋之后，我們徹底訪問不到它了，要知道真實情況 是我們町以通過base來訪問父類原來的方法的。接卜來就是實現(xiàn)這個了C# class MyBaseClasspublic Action SomeAction get, pnvate set, Stack<Action> previous Actions,protected void AddSomeAction(Action newMethod) p

4、reviousActions Push(S omeAction)t SomeAction = newMethod,protected void RemoveSomeActionOif(previousActions Count = 0)return,SomeAction = previousActions.PopO,public MyBaseClassQpreviousActions = new Stack<Action>0>Some Action = 0 => /Do sometliing!,class MyBaseClasspublic Action Some Ac

5、tion get, pnvate set, Stack<Action> previous Actionsfprotected void AddSomeAction(Action newMethod)previousActions Push(S ome Action),SomeAction = newMethod,protected void RemoveSomeActionOif(previousActions Count = 0)return,SomeAction = previousActions PopO,public MyBaseClassOpreviousActions

6、= new Stack<Action>0»SomeAction = 0 =/Do somethingi»上面的代碼中，我們通過AddSomeAction來實現(xiàn)覆溢的同時，將原來的方法保存在 previousActions中。這樣我們就可以保持兩者同時存在了。人家知道子類是不能覆蓋父類的靜態(tài)方法的，但是假設(shè)我們想實現(xiàn)靜態(tài)方法的覆蓋呢？C# void MainQvar mother = HotD aughtei' Activ atorO Messa ge,/mother =111 am the mother1var create = new HotDaugh

7、tei*0,var daughter = HotDaughter Activ atorO Message,/daughter = BI am the daughter1class CoolMotherpublic static Fuiic<Coolhlotlier> Activator get, protected set, /We are only doing this to avoid NULL references!static CoolMotherOActivator = 0 => new CoolMotherO,public CoolMotherO/Message

8、of eveiy motherMessage = "I am tlie mother1,public string Message get, protected set, class HotDaughtei' Coolhlotherpublic HotDaughtei'O/Once this constructor has been touched1 we set the Activator Activator = 0 => new HotDaughterO,/Message of eveiy daughtei*Message = MI am tlie daug

9、hter*,voidMainOvar mother = HotD aughtei* Activ atorO Message,/mother =111 am the mother"var create = new HotDaughtei'O,var daughter = HotDaughter Activ atorO Message,/daugliter = BI am the daughter*class CooMotherpublic static Func<Coolhfotlier> Activator get. protected set, /We are

10、only doing tins to avoid NULL refei'encesistatic CoolMotherOActivator = 0 => new CoolMotherO,public CoolMotherO/Message of eveiy motherMessage = "I am the mother-,public string Message get, protected set, class HotDaughtei* Coolhlotherpublic HotDaughtei'O/Once this constructor has be

11、en "touched* we set the Activator .Activator = 0 => new HotDaughtei'O,/Message of eveiy daughterhlessage = "I am tlie daughter",這里還是利用了將Lambda表達式作為屬性，町以隨時重新賦值的特點。當然這只是一個簡 單的示例，真實項目中并不建議人家這么去做。方法字典實際上這個模式我們在上一篇的返回方法中已經(jīng)講到了，只是沒有這樣一個名字而已，就算 是一個總結(jié)吧。故事是這樣的，你是不是經(jīng)常會寫到switch-case語句的時候覺得

12、不夠優(yōu)雅？ 但是你又不想去整個什么工廠模式或者策略模式，那怎么樣讓你的代碼看起來高級一點呢？public Action GetFmalizer(sti'ing input)switchcase "random":return ()=>/. / ,case11 dynamic":return ()=>/* . / ,defaultreturn ()=>/. / ,/變身之后Dictionaiy<sfa'ing, Action> finalizers,public void BuildFinalizersOfinalize

13、rs = new Dictionary vstring, Action。, finalizers AddCrandom11, ()=>/ . */ ); finalizers Add("dynamic"t ()=>/* . / ).public Action GetFinahzer(sti'ing input)if(fuializei-s ContainsKey(input) return finalizersinput,return ()=>/ . */ ,public Action GetFmalizer(sti'ing input)s

14、witchcase "random":return ()=>/. / ,case11 dynamic1':return ()=>/* . / ,defaultreturn ()=>/. / ,/變身之后Dictionaiy<sfa'ing> Action> finalizei's,public void BuildFinalizersOfinalizeis = new Dictionaryvstring, Action>0,finalizers AddCrandom11，0 => /* */ ),fma

15、lizers Add("dynamic"t 0 => /*. */ ),public Action GetFinalizer(string input)if(finahzers ContainsKey(input)return fiiializersinput,return 0 => / . */ ,好像看起來是不一樣了，有那么一點味道。但是一想是所有的方法都要放到那個 BuildFinalizei-s里面，這種組織方法實在是難以接受，我們來學學插件開發(fā)的方式，讓它自 己去找所有我們需要的方法。C#static Dictionaryvstnng, Action&

16、gt; finalizers,/在靜態(tài)的構(gòu)造函數(shù)用調(diào)用這個方法public static void BuildFinalizersOfinalizes = new DictionaryVstnng, Action。，/獲得當前運行程序集下所有的類型var types = Assembly GetExecutingAssemb lyO, GetTyp es()»foreacli(vai' type in types)檢查類型，我們町以提前定義接11或抽象類 if(type.IsSubclassOf(typeof(hlyMothei-Class) /獲得默認無參構(gòu)造函數(shù)var m

17、 = type GetConstructor(Type EmptyTypes),/調(diào)用這個默認的無參構(gòu)造函數(shù)if(m i=null) var instance = m Invoke(null) as MyMotlierClass, var nanie = type Name Removed Jdother"), var method = instance Method, finalizers Add(name, method),public Action GetFmalizer(stnng input)if(finalizers ContainsKey(input)return fm

18、alizersinput,return ()=>/*/ ,static Dictionaryvstring, Action> finalizers,/在靜態(tài)的構(gòu)造兩數(shù)用調(diào)用這個方法public static void BuildFinalizersf)finalizers = new Dictionary<sti*ing, Action。，/獲得當前運行程序集F所有的類型var types = Assembly GetExecutingAssemblyO.GetTypesO,foreach(var type in types)/檢查類型，我們可以提前定義接11或抽彖類 if(

19、type IsSubclassOf(typeof(MyMotherClass) /獲得默認無參構(gòu)造函數(shù)varm = type GetConstnjctor(TypeEinptyTypes),/調(diào)用這個默認的無參構(gòu)造函數(shù)if(m != null)var instance = m Invoke(null) as MyMotherClass,var name = type Name Remove(Mother1)»var method = mstance MyMethod, finalizeis Add(name, method),public Action GetFinalizer(st

20、ring input)if(fnializers. C onta insKey (input)return finalizersinput,return ()=>/ . */ ,如果要實現(xiàn)插件化的話，我們不光要能夠加截本程序集卞的方法，還要能隨時甚至運行時去 加載外部的方法，請繼續(xù)往下看：C# internal static void BuildlnitialFinalizersOfinalizes = new Dictionaryvstnng” Action>0>LoadPlugin(Assembly GetExecutingAssemblyO)> public st

21、atic void LoadPlugm(Assembly assembly)var types = assembly GetTypesO, foreacli(vai' type ni types)if(type IsSubclassOf(typeof(MyMothei'Class)var m = type GetConstnictor(Type EmptyTypes), if(m i= null)var instance = m lnvoke(null) as MyblotherClass,var name = type Name Remove(Mother1)»var method = instance MyMethod, fmalizers Add(name, method), int