如果对象为空，我想防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))
and
if (data != null)
然而，我在datlist . add (data)收到一个NullReferenceException。如果对象为空，它甚至不应该输入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<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;
}
如果这是检查对象是否为空的正确方法，那么我做错了什么(如何防止对对象进行进一步处理以避免NullReferenceException)?
public static bool isnull(object T)
{
return T == null ? true : false;
}
use:
isnull(object.check.it)
有条件的使用:
isnull(object.check.it) ? DoWhenItsTrue : DoWhenItsFalse;
更新(另一种方式)更新于2017年8月31日和2021年1月25日。谢谢你的评论。
public static bool IsNull(object T)
{
return (bool)T ? true : false;
}
骨干示范
为了记录，你在Github上有我的代码，去看看吧:
https://github.com/j0rt3g4/ValidateNull
PS:这一点是特别为你准备的，Chayim Friedman，不要使用测试软件，假设这一切都是真的。等待最终版本或使用您自己的环境进行测试，然后在没有任何文档或演示的情况下假设真正的beta软件。
[编辑以反映@kelton52的提示]
最简单的方法是做对象。ReferenceEquals (null,数据)
由于(null==data)不保证工作:
class Nully
{
public static bool operator ==(Nully n, object o)
{
Console.WriteLine("Comparing '" + n + "' with '" + o + "'");
return true;
}
public static bool operator !=(Nully n, object o) { return !(n==o); }
}
void Main()
{
var data = new Nully();
Console.WriteLine(null == data);
Console.WriteLine(object.ReferenceEquals(null, data));
}
生产:
比较"和" Nully "
真正的
假
正如其他人已经指出的那样，它不是data，而是dataList是null。除此之外……
catch-throw is an antipattern that almost always makes me want to throw up every time that I see it. Imagine that something goes wrong deep in something that doOtherStuff() calls. All you get back is an Exception object, thrown at the throw in AddData(). No stack trace, no call information, no state, nothing at all to indicate the real source of the problem, unless you go in and switch your debugger to break on exception thrown rather than exception unhandled. If you are catching an exception and just re-throwing it in any way, particularly if the code in the try block is in any way nontrivial, do yourself (and your colleagues, present and future) a favor and throw out the entire try-catch block. Granted, throw; is better than the alternatives, but you are still giving yourself (or whoever else is trying to fix a bug in the code) completely unnecessary headaches. This is not to say that try-catch-throw is necessarily evil per se, as long as you do something relevant with the exception object that was thrown inside the catch block.
然后，首先就存在捕获Exception的潜在问题，但这是另一回事，特别是因为在这种特殊情况下，您抛出了一个异常。
另一件让我感到非常危险的事情是，数据可能在函数执行期间更改值，因为您是通过引用传递的。因此，null检查可能会通过，但在代码对值进行任何操作之前，它已经被更改了——可能是null。我不确定这是否值得关注(可能不是)，但这似乎值得关注。
