在c# >中使用if (obj是null)

非空用: c# 7-8: if (obj是对象) c# 9: if (obj不为空)

它们将忽略由对象定义的任何==或!=(当然，除非您想将它们用于空检查)

欲了解更多，请参阅c#语言参考，见is运算符。

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。

从c# 8开始，你可以使用'empty'属性模式(带模式匹配)来确保对象不为空:

if (obj is { })
{
    // 'obj' is not null here
}

这种方法意味着“如果对象引用了某个对象的实例”(即它不是空的)。

你可以把它看作是:if (obj is null)....的对立面当对象没有引用某个对象的实例时，返回true。

有关c# 8.0模式的更多信息，请阅读这里。

[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

当你创建类的对象时，你必须使用下面的代码检查对象是否为空。

例子: Object1是类的对象

void myFunction(object1)
{
  if(object1!=null)
  {
     object1.value1 //If we miss the null check then here we get the Null Reference exception
  }
}

我做了更简单的(积极的方式)，似乎效果很好。

因为任何一种“对象”至少是一个对象

    if (MyObj is Object)
    {
            //Do something .... for example:  
            if (MyObj is Button)
                MyObj.Enabled = true;
    }