是返回null缺少的属性，而不是一个RunTimeBinderException .NET DynamicObject实施

Question

我希望能够做到像下面这样：

dynamic a = new ExpandoObject(); 
Console.WriteLine(a.SomeProperty ?? "No such member"); 

但抛出

RunTimeBinderException: 'System.Dynamic.ExpandoObject' does not contain a definition for 'Throw' 

你知道动态对象的实现将返回null为缺少的定义，或如何创建一个教程？非常感谢！

Answer 1

是这样的？

using System; 
using System.Collections.Generic; 
using System.Dynamic; 

public class NullingExpandoObject : DynamicObject 
{ 
    private readonly Dictionary<string, object> values 
     = new Dictionary<string, object>(); 

    public override bool TryGetMember(GetMemberBinder binder, out object result) 
    { 
     // We don't care about the return value... 
     values.TryGetValue(binder.Name, out result); 
     return true; 
    } 

    public override bool TrySetMember(SetMemberBinder binder, object value) 
    { 
     values[binder.Name] = value; 
     return true; 
    } 
} 

class Test 
{ 
    static void Main() 
    { 
     dynamic x = new NullingExpandoObject(); 
     x.Foo = "Hello"; 
     Console.WriteLine(x.Foo ?? "Default"); // Prints Hello 
     Console.WriteLine(x.Bar ?? "Default"); // Prints Default 
    } 
} 

我希望真正的ExpandoObject是相当比这更复杂，但如果这是你所需要的...