在 C# 中检查对象是否为空 [英] Checking if an object is null in C#
问题描述
如果对象为空，我想阻止对其进行进一步处理.
在下面的代码中，我检查对象是否为空:
if (!data.Equals(null))和
if (data != null)但是，我在 dataList.Add(data) 收到一个 NullReferenceException.如果对象为空，它甚至不应该进入 if 语句！
因此，我在问这是否是检查对象是否为空的正确方法:
public List如果这是检查对象是否为空的正确方法，我做错了什么(如何防止对对象进行进一步处理以避免 NullReferenceException)?
null 不是data，而是dataList.
您需要创建一个
public List更好:因为它是一个字段，所以将其设为私有.如果没有什么可以阻止您，请将其设置为 readonly.只是很好的做法.
旁边
检查无效性的正确方法是if(data != null).这种检查在引用类型中无处不在；甚至 Nullable<T> 覆盖了相等运算符，以便在检查 null 性时更方便地表达 nullable.HasValue.
如果你执行 if(!data.Equals(null)) 那么你会得到一个 NullReferenceException 如果 data == null.这有点可笑，因为避免这种例外是首要目标.
你也在这样做:
catch(异常 e){抛出新的异常(e.ToString());}这绝对不好.我可以想象你把它放在那里只是为了你可以在方法内部时进入调试器，在这种情况下忽略这一段.否则，不要无缘无故地捕获异常.如果你这样做了，只需使用 throw; 重新抛出它们.
I would like to prevent further processing on an object if it is null.
In the following code I check if the object is null by either:
if (!data.Equals(null))
and
if (data != null)
However, I receive a NullReferenceException at dataList.Add(data). If the object was null, it should never have even entered the if-statement!
Thus, I'm asking if this is proper way of checking if an object is null:
public List<Object> dataList;
public bool AddData(ref Object data)
bool success = false;
try
{
// I've also used "if (data != null)" which hasn't worked either
if (!data.Equals(null))
{
//NullReferenceException occurs here ...
dataList.Add(data);
success = doOtherStuff(data);
}
}
catch (Exception e)
{
throw new Exception(e.ToString());
}
return success;
}
If this is the proper way of checking if the object is null, what am I doing wrong (how can I prevent further processing on the object to avoid the NullReferenceException)?
It's not data that is null, but dataList.
You need to create one with
public List<Object> dataList = new List<Object>();
Even better: since it's a field, make it private. And if there's nothing preventing you, make it also readonly. Just good practice.
Aside
The correct way to check for nullity is if(data != null). This kind of check is ubiquitous for reference types; even Nullable<T> overrides the equality operator to be a more convenient way of expressing nullable.HasValue when checking for nullity.
If you do if(!data.Equals(null)) then you will get a NullReferenceException if data == null. Which is kind of comical since avoiding this exception was the goal in the first place.
You are also doing this:
catch (Exception e)
{
throw new Exception(e.ToString());
}
This is definitely not good. I can imagine that you put it there just so you can break into the debugger while still inside the method, in which case ignore this paragraph. Otherwise, don't catch exceptions for nothing. And if you do, rethrow them using just throw;.
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