C#高级编程9-第12章 动态语言扩展

C#高级编程9-第12章 动态语言扩展

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dynamic t = new ExpandoObject();
t.Abc = "abc";
t.Value = ;
Console.WriteLine(t.Abc);
t.Abc = "";
Console.WriteLine(t.Abc);

dynamic动态类型的值是可读可写的，它是编译型语言，而Javascript是解释性语言.因此JavaScript定义后可以引用它。而dynamic定义后，无法引用它，无法获知它的类型是什么.只有编译运行时才能获得它的类型.
因此当我们无法获知它的类型时就会出现未知的异常，比如说类型转换异常、序列化异常、对象或属性不存在等等。因此对于使用dynamic时常常需要处理系统异常。

对于dynamic动态类型,它仅仅是一种类型，对于var类型它可以是一种序列化的字符串.

 dynamic t = new ExpandoObject();
 t.Abc = "abc";
 t.Value = ;
 Console.WriteLine(t.Abc);
 t.Abc = "";
 Console.WriteLine(t.Abc);

 Console.WriteLine(t.ToString());

 var t2 = new { Abc = "abc", Value =  };
 Console.WriteLine(t2.ToString());

对于var而言它可以声明后立即使用它，但是它的优点是如果var声明的成员它是只读的。但是声明成员值是可以修改的.

var t2 = new { Abc = "abc", Value = new { Item= new Person() } };

对于dynamic 而言，它声明后也可以立即使用它，它的成员可读可写，但是它是没有类型的需要编码者判断其来源和属性。

DynamicObejct 是所有动态类的基类，可以从其继承以实现自己的动态对象。ExpandoObject 是一个sealed 类，已经封装好了所有方法。

static void Main(string[] args)

        {

            dynamic dynamicObject = new MyDynamicObject();

            dynamicObject.FirstName = "Alan";

            dynamicObject.LastName = "Yang";

            dynamicObject.Age = ;

            Action<dynamic> show = (item) => Console.WriteLine("My name is " + item.FirstName + " " + item.LastName

                                                               + ". I'm " + item.Age + " years old.");

            dynamicObject.Show = show;

            dynamicObject.Show(dynamicObject);

            Console.Read();

        }

public class MyDynamicObject : DynamicObject

    {

        Dictionary<string, object> _dynamicData = new Dictionary<string, object>();

        public override bool TryGetMember(GetMemberBinder binder, out object result)

        {

            bool success = false;

            result = null;

            if (_dynamicData.ContainsKey(binder.Name))

            {

                result = _dynamicData[binder.Name];

                success = true;

            }

            else

            {

                result = "Property Not Found!";

                success = false;

            }

            return success;

        }

        public override bool TrySetMember(SetMemberBinder binder, object value)

        {

            _dynamicData[binder.Name] = value;

            return true;

        }

        public override bool TryInvokeMember(InvokeMemberBinder binder,

        object[] args,

        out object result)

        {

            result = true;

            dynamic method = _dynamicData[binder.Name];

            method(args[]);

            return true;

        }

    }

ExpandoObject

static void Main(string[] args)

       {

           dynamic dynamicObject = new ExpandoObject();

           dynamicObject.FirstName = "Alan";

           dynamicObject.LastName = "Yang";

           dynamicObject.Age = ;

           Action<dynamic> show = (item) => Console.WriteLine("My name is " + item.FirstName + " " + item.LastName

                                                              + ". I'm " + item.Age + " years old.");

           dynamicObject.Show = show;

           dynamicObject.Show(dynamicObject);

           Console.Read();

       }

ViewBag

public dynamic ViewBag

      {

          get

          {

              if (_dynamicViewData == null)

              {

                  _dynamicViewData = new DynamicViewDataDictionary(() => ViewData);

              }

              return _dynamicViewData;

          }

      }

DynamicViewDataDictionary 类的定义为：

using System.Collections.Generic;

using System.Diagnostics;

using System.Dynamic;

namespace System.Web.Mvc

{

    internal sealed class DynamicViewDataDictionary : DynamicObject

    {

        private readonly Func<ViewDataDictionary> _viewDataThunk;

        public DynamicViewDataDictionary(Func<ViewDataDictionary> viewDataThunk)

        {

            _viewDataThunk = viewDataThunk;

        }

        private ViewDataDictionary ViewData

        {

            get

            {

                ViewDataDictionary viewData = _viewDataThunk();

                Debug.Assert(viewData != null);

                return viewData;

            }

        }

        // Implementing this function improves the debugging experience as it provides the debugger with the list of all

        // the properties currently defined on the object

        public override IEnumerable<string> GetDynamicMemberNames()

        {

            return ViewData.Keys;

        }

        public override bool TryGetMember(GetMemberBinder binder, out object result)

        {

            result = ViewData[binder.Name];

            // since ViewDataDictionary always returns a result even if the key does not exist, always return true

            return true;

        }

        public override bool TrySetMember(SetMemberBinder binder, object value)

        {

            ViewData[binder.Name] = value;

            // you can always set a key in the dictionary so return true

            return true;

        }

    }

}