C#有用Null Conditional Operator。在this answer也做了很好的解释。
当我的对象是动态/ expando对象时,我想知道是否可以像这样进行类似的检查。让我给你看一些代码:
鉴于此类层次结构
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空检查,它可以正常工作
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,我将尝试使用动态(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.
}
有没有办法用动态模拟这种行为?我的意思是,检查长链成员中的空值?
答案 0 :(得分:4)
如果您想以更自然的方式支持它,您可以从DynamicObject继承并提供自定义实现:
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。
我们在这里做的是每次找不到属性时都会返回 TryGetMember 的输出参数的 null 引用,并且我们总是返回true。
答案 1 :(得分:0)
编辑:修复,因为ExpandoObjects和扩展方法不能很好地协同工作。稍微不那么好,但希望仍然有用。
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)