c# - 为什么我不能在隐式转换时返回接口(interface)，而 ExpandoObject 可以？

Question

我有一个 DynamicObject我希望它可以转换为 IDictionary，与 ExpandoObject 完全相同.例如，将 ExpandoObject 转换为 IDictionary 是完全有效的:

dynamic ex = new ExpandoObject ();
ex.Field = "Foobar";
IDictionary<string, object> dict = ex as IDictionary<string, object>;
Console.WriteLine (dict["Field"]);

现在我尝试将它实现到我自己的 DynamicObject 中:

public class MyDynamicObject : DynamicObject
{
    public Dictionary<string, object> members = new Dictionary<string, object> ();

    public override bool TryGetMember (GetMemberBinder binder, out object result)
    {
        if (members.ContainsKey (binder.Name)) {
            result = members[binder.Name];
            return true;
        }
        else {
            result = null;
            return false;
        }
    }
    public override bool TrySetMember (SetMemberBinder binder, object value)
    {
        this.members.Add (binder.Name, value);
        return true;
    }
    public static implicit operator IDictionary<string, object> (MyDynamicObject mydo) 
    {
        return (IDictionary<string, object>) mydo.members;
    }
}

但是编译器会在 public static implicit operator IDictionary<string, object> 上失败行，给出错误:“无法转换为接口(interface)类型或从接口(interface)类型转换”。如果我将隐式运算符更改为 Dictionary，我可以毫无问题地将 MyDynamicObject 转换为 Dictionary，但不能转换为 IDictionary。

ExpandoObject 如何做到这一点？

Answer 1

ExpandoObject 简单地实现 IDictionary<string, object> .

如果你想有相同的行为，你还需要实现这个接口(interface)并将所有调用委托(delegate)给你的 members字段。

像这样:

public class MyDynamicObject : DynamicObject, IDictionary<string, object>
{
    public Dictionary<string, object> members = new Dictionary<string, object>();

    public IEnumerator<KeyValuePair<string, object>> GetEnumerator()
    {
        return members.GetEnumerator();
    }

    public void Add(KeyValuePair<string, object> item)
    {
        members.Add(item.Key, item.Value);
    }

    // ...
}