ExpandoObject 的真正好处是什么? [英] What are the true benefits of ExpandoObject?

问题描述

ExpandoObject 类添加到 .NET 4 后，您可以在运行时将属性任意设置到对象上.

The ExpandoObject class being added to .NET 4 allows you to arbitrarily set properties onto an object at runtime.

与使用 Dictionary<string 相比，这有什么优势吗?object>，甚至是 哈希表?据我所知，这只不过是一个哈希表，您可以使用更简洁的语法访问它.

Are there any advantages to this over using a Dictionary<string, object>, or really even a Hashtable? As far as I can tell, this is nothing but a hash table that you can access with slightly more succinct syntax.

例如，这是为什么:

dynamic obj = new ExpandoObject();
obj.MyInt = 3;
obj.MyString = "Foo";
Console.WriteLine(obj.MyString);

确实比:

var obj = new Dictionary<string, object>();
obj["MyInt"] = 3;
obj["MyString"] = "Foo";

Console.WriteLine(obj["MyString"]);

使用 ExpandoObject 而不是仅使用任意字典类型可以获得哪些真正优势，除了不明显您使用的是将在运行时确定的类型.

What real advantages are gained by using ExpandoObject instead of just using an arbitrary dictionary type, other than not being obvious that you're using a type that's going to be determined at runtime.

推荐答案

既然我写了你所指的 MSDN 文章，我想我必须回答这个问题.

Since I wrote the MSDN article you are referring to, I guess I have to answer this one.

首先，我预料到了这个问题，这就是为什么我写了一篇博客文章，展示了 ExpandoObject 或多或少的真实用例:C# 4.0 中的动态:ExpandoObject 简介.

First, I anticipated this question and that's why I wrote a blog post that shows a more or less real use case for ExpandoObject: Dynamic in C# 4.0: Introducing the ExpandoObject.

很快，ExpandoObject 可以帮助您创建复杂的分层对象.例如，假设您在字典中有一个字典:

Shortly, ExpandoObject can help you create complex hierarchical objects. For example, imagine that you have a dictionary within a dictionary:

Dictionary<String, object> dict = new Dictionary<string, object>();
Dictionary<String, object> address = new Dictionary<string,object>();
dict["Address"] = address;
address["State"] = "WA";
Console.WriteLine(((Dictionary<string,object>)dict["Address"])["State"]);

层次越深，代码越丑.使用 ExpandoObject，它保持优雅和可读性.

The deeper is the hierarchy, the uglier is the code. With ExpandoObject it stays elegant and readable.

dynamic expando = new ExpandoObject();
expando.Address = new ExpandoObject();
expando.Address.State = "WA";
Console.WriteLine(expando.Address.State);

其次，正如已经指出的那样，ExpandoObject 实现了 INotifyPropertyChanged 接口，它使您可以比字典更好地控制属性.

Second, as it was already pointed out, ExpandoObject implements INotifyPropertyChanged interface which gives you more control over properties than a dictionary.

最后，您可以像这样向 ExpandoObject 添加事件:

Finally, you can add events to ExpandoObject like here:

class Program
{
   static void Main(string[] args)
   {
       dynamic d = new ExpandoObject();

       // Initialize the event to null (meaning no handlers)
       d.MyEvent = null;

       // Add some handlers
       d.MyEvent += new EventHandler(OnMyEvent);
       d.MyEvent += new EventHandler(OnMyEvent2);

       // Fire the event
       EventHandler e = d.MyEvent;

       e?.Invoke(d, new EventArgs());
   }

   static void OnMyEvent(object sender, EventArgs e)
   {
       Console.WriteLine("OnMyEvent fired by: {0}", sender);
   }

   static void OnMyEvent2(object sender, EventArgs e)
   {
       Console.WriteLine("OnMyEvent2 fired by: {0}", sender);
   }
}

另外，请记住，没有什么可以阻止您以动态方式接受事件参数.换句话说，您可以使用 EventHandler 而不是使用 EventHandler，这会导致处理程序的第二个参数为 dynamic.

Also, keep in mind that nothing is preventing you from accepting event arguments in a dynamic way. In other words, instead of using EventHandler, you can use EventHandler<dynamic> which would cause the second argument of the handler to be dynamic.

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