blocks|key|3465728|text|这里已经介绍了这一点：Detecting+what+the+target+object+is+when+NullReferenceException+is+thrown|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|3465729|这里：Why+can't+a+null-reference+exception+name+the+object+that+has+a+null+reference?|3465730|主要原因是运行时不知道何时会遇到NRE。我猜它必须返回callstack并通过解析树，这将是非常昂贵的。|3465731|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/115573/detecting-what-the-target-object-is-when-nullreferenceexception-is-thrown|1|https://stackoverflow.com/questions/578734/why-cant-a-null-reference-exception-name-the-object-that-has-a-null-reference^0|B|21|0|0|3|27|1|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@$A|S|B|T|1|U]]|C|$]]|$1|D|3|E|5|6|7|V|8|@]|9|@$A|W|B|X|1|Y]]|C|$]]|$1|F|3|G|5|6|7|Z|8|@]|9|@]|C|$]]|$1|H|3|-4|5|6|7|10|8|@]|9|@]|C|$]]]|I|$J|$5|K|L|M|C|$N|O]]|P|$5|K|L|M|C|$N|Q]]]]

This has been covered here: <a href="https://stackoverflow.com/questions/115573/detecting-what-the-target-object-is-when-nullreferenceexception-is-thrown">Detecting what the target object is when NullReferenceException is thrown</a> 

and here: <a href="https://stackoverflow.com/questions/578734/why-cant-a-null-reference-exception-name-the-object-that-has-a-null-reference">Why can&#39;t a null-reference exception name the object that has a null reference?</a>

The reason is mainly cause the runtime has no idea when the NRE is encountered. My guess it that it would have to work back the callstack and through the parse tree, which would be really expensive.

blocks|key|3252644|text|我并不觉得这个异常很难处理！|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3252645|如果我知道行号的话。我只需在此行插入一个断点，运行应用程序到此行，当调试器停止时，我悬停在该行中的每个变量/对象上，多亏了Visual+Studio，它向我显示了它们的值。|3252646|此外，我发现Autos窗口在这种情况下非常有用，但我上面描述的过程很快就解决了我的问题。|3252647|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

I did not find this exception that hard to deal with!

If I know the line number. I just insert a breakpoint at this line, run the application to this line, and when the debugger stops, I hover every variable/object in the line, and thanks to Visual Studio, it shows me their values.

Also I found Autos window very helpful in such cases, but the procedure I described above solves my problem quickly.

blocks|key|409740|text|ArgumentNullException和NullReferenceException的不同之处在于，ArgumentNullException总是像这样显式抛出：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|409741|if+(parameter+==+null)
++throw+new+ArgumentNullException("parameter");|code-block|syntax|javascript|409742|快速查看一下ILDASM输出，局部变量确实存在于函数的IL中。然而，仍然没有API来以编程方式检索这些名称。我的理解是，这将是相当复杂的，因为你基本上需要构建一个解析树来表示一个带有作用域、变量、语句等的函数。|409743|更复杂的是，抛出NullReferenceException的不只是简单的变量，还有函数调用、属性或表达式的结果。我可以很快变得非常复杂。|409744|想象一下：|409745|internalObject.OtherProperty+=+myObject.GetOtherObject().ThirdObject.SomeProperty+==+"value"
+?+myObject.OtherProperty
+:+myObject.GetSomethingElse();|409746|这里有多个故障点，构建一个表示实际null的字符串可能很棘手。|409747|entityMap^0|0|L|M|M|1G|L|0|0|0|8|M|0|0|0|H|4|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|13|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|14|8|@]|D|@]|E|$]]|$1|M|3|N|5|6|7|15|8|@$9|16|A|17|B|C]]|D|@]|E|$]]|$1|O|3|P|5|6|7|18|8|@]|D|@]|E|$]]|$1|Q|3|R|5|H|7|19|8|@]|D|@]|E|$I|J]]|$1|S|3|T|5|6|7|1A|8|@$9|1B|A|1C|B|C]]|D|@]|E|$]]|$1|U|3|-4|5|6|7|1D|8|@]|D|@]|E|$]]]|V|$]]

The difference between <code>ArgumentNullException</code> and <code>NullReferenceException</code> is that <code>ArgumentNullException</code> is always thrown explicitly like so:

<pre><code>if (parameter == null)
 throw new ArgumentNullException("parameter");
</code></pre>

Had a quick look at ILDASM output, the local variables are indeed present inside a function's IL. There is still, however, no API to retrieve those names programatically. My understanding is that it would be fairly complex as you would basically need to build a parse tree that represents a function with scopes, variables, statements etc.

It's further complicated by the fact that it's not just simple variables that can throw <code>NullReferenceException</code>, but result of a function call, a property or an expression. I could get pretty complicated pretty fast.

Imagine this:

<pre><code>internalObject.OtherProperty = myObject.GetOtherObject().ThirdObject.SomeProperty == "value"
 ? myObject.OtherProperty
 : myObject.GetSomethingElse();
</code></pre>

There are multiple points of failure there and building up a string representing what is actually <code>null</code> could be tricky.

blocks|key|3252676|text|即使变量名称和类型可能存在于MSIL代码中，当MSIL为JITted时，它也不会存在于本机代码中。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3252677|在JITting期间，将这种检查添加到本机代码中将是非常低效的--本质上是当指针被解除引用时的开销。|3252678|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

Even though the variable name and type may exist in the MSIL code, it won't exist in the native code when the MSIL is JITted.

It would be incredibly inefficient to add this kind of check to the native code during JITting - essentially an overhead whenever a pointer is dereferenced.

"Object reference not set to an instance of an object"

Why does the exception not also show the name of the object reference field, or at least its type?

This is probably one of the most common run-time errors in .NET. Although the System.Exception has a stack trace, there are no other helpful details.

Over the course of a year I spend hours sifting through stack traces (often in code I did not write), hoping there is a line number from a ".pdb" file, then finding the line in the code, and even then it is often not obvious which reference on the line was null. Having the name of the reference field would be very convenient. 

If System.ArgumentNullException instances can show the name of the method parameter ("Value cannot be null. Parameter name: value"), then surely System.NullReferenceException instances could include the name of the null field (or its containing collection).

"Object reference not set to an instance of an object": why can't .NET show more details?

Visual Studio

调试器

“未将对象引用设置为对象的实例”为什么异常不显示object reference字段的name，或者至少显示它的类型？这可能是.NET中最常见的运行时错误之一，虽然System.Exception有堆栈跟踪，但没有其他有用的细节。在一年的时间里，我花了几个小时筛选堆栈跟踪(通常是在我没有编写的代码中)，希望有来自".p...

问"Object reference not set to an object instance“：为什么.NET不能显示更多细节？
EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问"Object reference not set to an object instance“：为什么.NET不能显示更多细节？EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问"Object reference not set to an object instance“：为什么.NET不能显示更多细节？
EN