C# 有有用的空条件运算符。很好地解释了这个答案 too.
我想知道当我的对象是动态/扩展对象时是否可以进行类似的检查。让我向您展示一些代码:
给定这个类的层次结构
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()
{
}
}
如果我执行这种链接空检查,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,我将尝试用动态(ExpandoObject)重现这种行为
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模拟这种行为?我的意思是,检查一长串成员中是否存在空值?
如果您想以更自然的方式支持这一点,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;
}
}
Testing:
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“它有效!”。由于 Boo 不存在,我们得到一个空引用,以便空条件运算符可以工作。
我们在这里所做的是返回一个null参考输出参数尝试获取会员每次没有找到属性时,我们总是返回 true。
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