是返回null缺少的屬性，而不是一個RunTimeBinderException .NET DynamicObject實施

Question

我希望能夠做到像下面這樣：

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

但拋出

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

你知道動態對象的實現將返回null爲缺少的定義，或如何創建一個教程？非常感謝！

Answer 1

是這樣的？

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是相當比這更復雜，但如果這是你所需要的...