Implementing Dynamic Interfaces

名词解释

DLR: dynamic language runtime.

refer to this article:http://msdn.microsoft.com/en-us/vstudio/ff800651.aspx

下面是一个简单的实现，会动态的创建需要的属性：

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

            try
            {
                Console.WriteLine(dynamicProperties.Marker);
            }
            catch (Microsoft.CSharp.RuntimeBinder.RuntimeBinderException)
            {
                Console.WriteLine("There is no such a property.");
            }

            dynamicProperties.Date = DateTime.Now;
            dynamicProperties.Name = "Bill Wagner";
            dynamicProperties.Title = "Effective C#";
            dynamicProperties.Content = "Building a dynamic dictionary";

            Console.WriteLine(dynamicProperties);
            Console.ReadLine();
        }
    }

    class MyDynamicObject : DynamicObject
    {
        private Dictionary<string, object> storage = new Dictionary<string, object>();
        public override bool TryGetMember(GetMemberBinder binder, out object result)
        {
            if (storage.ContainsKey(binder.Name))
            {
                result = storage[binder.Name];
                return true;
            }
            result = null;
            return false;
        }

        public override bool TrySetMember(SetMemberBinder binder, object value)
        {
            string key = binder.Name;
            if (storage.ContainsKey(key))
                storage[key] = value;
            else
                storage.Add(key, value);

            return true;
        }

        public override string ToString()
        {
            var sb = new StringBuilder();
            foreach (var item in storage)
                sb.AppendLine(string.Format("{0}:\t{1}", item.Key, item.Value));

            return sb.ToString();
        }
    }

更比较通用的是ExpandoObject类，可以在运行是动态的添加或删除成员，包括属性，事件等等。

例如，

1. 添加新属性：

dynamic sampleObject = new ExpandoObject();

sampleObject.test = "Dynamic Property";
Console.WriteLine(sampleObject.test);
Console.WriteLine(sampleObject.test.GetType());

2. 添加事件(lambda或event)：

// 2.1 add lambda expression

sampleObject.number = 10;
sampleObject.Increment = (Action)(() => { sampleObject.number++; });
// Before calling the Increment method.
Console.WriteLine(sampleObject.number);
sampleObject.Increment();
// After calling the Increment method.
Console.WriteLine(sampleObject.number);

// 2.2 add event

// Create a new event and initialize it with null. must declare it first.
sampleObject.sampleEvent = null;

 // Add an event handler.
sampleObject.sampleEvent += new EventHandler(SampleHandler);
 // Raise an event for testing purposes.
sampleObject.sampleEvent(sampleObject, new EventArgs());
 // Event handler.
 static void SampleHandler(object sender, EventArgs e)
 {
        Console.WriteLine("SampleHandler for {0} event", sender);
}

3. 作为参数传递

dynamic employee = new ExpandoObject();
employee.Name = "John Smith";
employee.Age = 33;

WritePerson(employee);

private static void WritePerson(dynamic person)

{
        Console.WriteLine("{0} is {1} years old.", person.Name, person.Age);

}
4. 枚举成员：

因为该类实现了IDictionary<string, object>接口，所以可以枚举它的成员。

dynamic employee = new ExpandoObject();
employee.Name = "John Smith";
employee.Age = 33;

foreach (var property in (IDictionary<String, Object>)employee)
{
    Console.WriteLine(property.Key + ": " + property.Value);
}
// This code example produces the following output:
// Name: John Smith
// Age: 33

// 删除某个成员
dynamic employee = new ExpandoObject();
employee.Name = "John Smith";
((IDictionary<String, Object>)employee).Remove("Name");

5. 通知机制
// Add "using System.ComponentModel;" line
// to the beginning of the file.
class Program
{
    static void Test()
    {
        dynamic employee = new ExpandoObject();
        ((INotifyPropertyChanged)employee).PropertyChanged +=
            new PropertyChangedEventHandler(HandlePropertyChanges);
        employee.Name = "John Smith";
    }

    private static void HandlePropertyChanges(
        object sender, PropertyChangedEventArgs e)
    {
        Console.WriteLine("{0} has changed.", e.PropertyName);
    }
}