.net DynamicObject 实现，为缺少的属性返回 null 而不是 RunTimeBinderException

Question

我希望能够执行以下操作：

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

但这会引发

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

您是否知道 DynamicObject 的一种实现，它会因缺少定义而返回 null，或者有关如何创建定义的教程？非常感谢！

Answer 1

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 比这更复杂，但如果这就是你所需要的......