如何检查对象是否为空的？ [英] How to check if an object is nullable?

问题描述

我如何检查，如果给定对象可为空，换句话说如何实现下面的方法...

How do I check if a given object is nullable in other words how to implement the following method...

bool IsNullableValueType(object o)
{
    ...
}

编辑：我在寻找空值类型。我没有裁判的类型记在心里。

I am looking for nullable value types. I didn't have ref types in mind.

//Note: This is just a sample. The code has been simplified 
//to fit in a post.

public class BoolContainer
{
	bool? myBool = true;
}

var bc = new BoolContainer();

const BindingFlags bindingFlags = BindingFlags.Public
						| BindingFlags.NonPublic
						| BindingFlags.Instance
						;


object obj;
object o = (object)bc;

foreach (var fieldInfo in o.GetType().GetFields(bindingFlags))
{
	obj = (object)fieldInfo.GetValue(o);
}

现在OBJ是指类型的对象布尔（<$ C C $>可选System.Boolean ）与价值等于真。我真正想要的是类型的对象可空＆LT;布尔＆GT;

obj now refers to an object of type bool (System.Boolean) with value equal to true. What I really wanted was an object of type Nullable<bool>

所以，现在作为一个变通，我决定检查如果o可为空，并创建一个围绕OBJ一个可空包装。

So now as a work around I decided to check if o is nullable and create a nullable wrapper around obj.

推荐答案

有两种类型的可空 - 可空＆LT; T＆GT; 和引用类型

There are two types of nullable - Nullable<T> and reference-type.

乔恩纠正我，这是很难得的类型，如果盒装的，但是你可以用仿制药：   - 所以怎么样在下面。这实际上是测试类型 T ，但使用 OBJ 纯粹是为了泛型类型推断（以方便调用参数） - 这是可行的，几乎没有相同的 OBJ 参数，但

Jon has corrected me that it is hard to get type if boxed, but you can with generics: - so how about below. This is actually testing type T, but using the obj parameter purely for generic type inference (to make it easy to call) - it would work almost identically without the obj param, though.

static bool IsNullable<T>(T obj)
{
    if (obj == null) return true; // obvious
    Type type = typeof(T);
    if (!type.IsValueType) return true; // ref-type
    if (Nullable.GetUnderlyingType(type) != null) return true; // Nullable<T>
    return false; // value-type
}

不过，这是行不通的这么好，如果你已经装箱的值对象变量。

But this won't work so well if you have already boxed the value to an object variable.

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