有没有办法在 dynamic/expando 中执行链式空检查？

Question

C# 也有有用的 Null Conditional Operator. Well explained in this answer。

我想知道当我的对象是 dynamic/expando 对象时是否可以像这样进行类似的检查。让我给你看一些代码：

鉴于此 class 层次结构

public class ClsLevel1
{
    public ClsLevel2 ClsLevel2 { get; set; }
    public ClsLevel1()
    {
        this.ClsLevel2 = new ClsLevel2(); // You can comment this line to test
    }        
}

public class ClsLevel2
{
    public ClsLevel3 ClsLevel3 { get; set; }
    public ClsLevel2()
    {
        this.ClsLevel3 = new ClsLevel3();
    }       
}

public class ClsLevel3
{
    // No child
    public ClsLevel3()
    {
    }
}

如果我执行这种链式 null 检查，它会起作用

ClsLevel1 levelRoot = new ClsLevel1();
if (levelRoot?.ClsLevel2?.ClsLevel3 != null)
{
     // will enter here if you DO NOT comment the content of the ClsLevel1 constructor
}
else
{
     // will enter here if you COMMENT the content of the ClsLevel1 
}

现在，我将尝试使用动力学 (ExpandoObjects) 重现此行为

dynamic dinRoot = new ExpandoObject();
dynamic DinLevel1 = new ExpandoObject();
dynamic DinLevel2 = new ExpandoObject();
dynamic DinLevel3 = new ExpandoObject();

dinRoot.DinLevel1 = DinLevel1;
dinRoot.DinLevel1.DinLevel2 = DinLevel2;
//dinRoot.DinLevel1.DinLevel2.DinLevel3 = DinLevel3; // You can comment this line to test

if (dinRoot?.DinLevel1?.DinLevel2?.DinLevel3 != null)
{
     // Obviously it will raise an exception because the DinLevel3 does not exists, it is commented right now.
}

有没有办法用动力学来模拟这种行为？我的意思是，检查一长串成员中的空值？

Answer 1

编辑：已修复，因为 ExpandoObjects 和扩展方法不能很好地协同工作。稍微不太好，但希望仍然可用。

辅助方法：

public static class DynamicExtensions
{
    public static Object TryGetProperty(ExpandoObject obj, String name)
    {
        return name.Split('.')
                   .Aggregate((Object)obj, (o, s) => o != null
                                                      ? TryGetPropertyInternal(o, s)
                                                      : null);
    }

    private static Object TryGetPropertyInternal(Object obj, String name)
    {
        var dict = obj as IDictionary<String, Object>;
        return (dict?.ContainsKey(name) ?? false) ? dict[name] : null;
    }
}

用法：

if (DynamicExtensions.TryGetProperty(dinRoot, "DinLevel1.DinLevel2.DinLevel3") != null)

Answer 2

如果您想以更自然的方式支持它，您可以继承 DynamicObject 并提供自定义实现：

class MyExpando : DynamicObject
    {
        private readonly Dictionary<string, object> _dictionary = new Dictionary<string, object>();

        public override bool TryGetMember(GetMemberBinder binder, out object result)
        {
            var name = binder.Name.ToLower();
            result = _dictionary.ContainsKey(name) ? _dictionary[name] : null;
            return true;
        }

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

测试：

 private static void Main(string[] args)
        {
            dynamic foo = new MyExpando();
            if (foo.Boo?.Lol ?? true)
            {
                Console.WriteLine("It works!");
            }
            Console.ReadLine();
        }

输出将是 "It works!"。由于 Boo 不存在，我们得到一个空引用，以便 Null 条件运算符可以工作。

我们这里做的就是return一个null引用TryGetMember的输出参数每次属性未找到，我们始终 return 为真。

有没有办法在 dynamic/expando 中执行链式空检查？

Is there a way to perform a chained null check in a dynamic/expando?

c#

.net

dynamic

expandoobject