你调用的对象是空的。 asp.net c＃ [英] object reference not set to an instance of an object. asp.net c#

问题描述

你好，





我在身份证附近得到错误...我无法解决这个问题..谁能告诉我为什么发生这种情况以及如何解决这个问题

hello,


im getting that error near ID...im unable to solve this..can anyone tell me why this occurs and how to solve that

GridEditFormInsertItem item = e.Item as GridEditFormInsertItem;
              int  ID = Int32.Parse(item["ID"].Text);
              string FirstName = (item["FirstName"].Controls[0] as RadTextBox).Text;
              string LastName = (item["LastName"].Controls[0] as RadTextBox).Text;

谢谢

Thank you

推荐答案

您可以在任何使用的行中抛出异常 item [some string] ;当它返回null时，稍后您尝试通过使用任何对象属性取消引用它，这会引发此异常。



您没有显示异常与抛出对象引用未设置为对象的实例。



不用担心。这是检测和修复的最简单的案例之一。它只是意味着某些引用类型的某个成员/变量通过使用和它的实例（非静态）成员解除引用，这要求此成员/变量为非null，但实际上它似乎为null。只需在调试器下执行它，它将停止抛出异常的执行。在该行上设置一个断点，重新启动应用程序并再次到达这一点。评估下一行中涉及的所有引用，并查看哪一个为null，而不需要为null。解决这个问题之后，修复代码：要么确保将成员/变量正确初始化为非空引用，要么将其检查为null，如果为null，则执行其他操作。



另请参阅：想要在按钮点击时显示下一条记录。但是如果下一条记录功能的条件对象引用没有设置为对象的实例 [ ^ ]。



有时候，你不能在调试器下，由于一个或另一个原因做到这一点。一个非常讨厌的情况是，只有在调试信息不​​可用时构建软件时才会出现问题。在这种情况下，你必须使用更难的方式。首先，你需要确保你永远不会通过静默处理异常来阻止异常的传播（这是开发人员对自己的犯罪，但很常见）。您需要在每个线程的最顶层堆栈帧上捕获绝对所有异常。如果处理类型 System.Exception 的异常，则可以执行此操作。在处理程序中，您需要记录所有异常信息，尤其是 System.Exception.StackTrace ：

http://msdn.microsoft.com/en-us/library/system.exception.aspx [ ^ ]，

http://msdn.microsoft.com/en-us/library/system.exception。 stacktrace.aspx [ ^ ]。



堆栈跟踪只是一个字符串，显示从throw语句到处理程序的异常传播的完整路径。通过阅读，您总能找到目的。对于日志记录，使用类 System.Diagnostics.EventLog ：

http://msdn.microsoft.com/en-us/library/system.diagnostics.eventlog.aspx [ ^ ]。

-SA

The exception could be thrown in any of the lines where you use item["some string"]; when it returns null, later on you try to dereference it by using any of the object properties, which throws this exception.

You did not show where the exception with the message "Object reference not set to an instance of an object" is thrown.

Not to worry. This is one of the very easiest cases to detect and fix. It simply means that some member/variable of some reference type is dereferenced by using and of its instance (non-static) members, which requires this member/variable to be non-null, but in fact it appears to be null. Simply execute it under debugger, it will stop the execution where the exception is thrown. Put a break point on that line, restart the application and come to this point again. Evaluate all references involved in next line and see which one is null while it needs to be not null. After you figure this out, fix the code: either make sure the member/variable is properly initialized to a non-null reference, or check it for null and, in case of null, do something else.

Please see also: want to display next record on button click. but got an error in if condition of next record function "object reference not set to an instance of an object"[^].

Sometimes, you cannot do it under debugger, by one or another reason. One really nasty case is when the problem is only manifested if software is built when debug information is not available. In this case, you have to use the harder way. First, you need to make sure that you never block propagation of exceptions by handling them silently (this is a crime of developers against themselves, yet very usual). The you need to catch absolutely all exceptions on the very top stack frame of each thread. You can do it if you handle the exceptions of the type System.Exception. In the handler, you need to log all the exception information, especially the System.Exception.StackTrace:
http://msdn.microsoft.com/en-us/library/system.exception.aspx[^],
http://msdn.microsoft.com/en-us/library/system.exception.stacktrace.aspx[^].

The stack trace is just a string showing the full path of exception propagation from the throw statement to the handler. By reading it, you can always find ends. For logging, it's the best (in most cases) to use the class System.Diagnostics.EventLog:
http://msdn.microsoft.com/en-us/library/system.diagnostics.eventlog.aspx[^].

Good luck,

—SA

我们分不清楚你究竟是为什么会遇到这个问题 - 实际的错误很可能是你的代码中的其他地方而且只是出现在这里。

但基本上，正在发生的是左边的一个元素一个 。是 null 。

例如：

We can't tell you exactly why you get the problem - it's likely that the actual fault is elsewhere in your code and is only showing up here.
But basically, what is happening is that one of the elements to the left of a "." is null.
For example:

string s = a.b.c.d.ToString();

如果 a 是 null ，你会收到错误。

如果 a 是一个值，但 ab null ，您将收到错误。

如果 ab 是一个值，但是 abc 是 null ...



你得到这个想法。



在给出错误的线上方的线上放置一个断点并使用鼠标依次悬停在每个部分上 - 找到哪一个 null 你可以开始寻找你的代码让它为空的原因。


对不起，但它已经结束了而且调试器，我担心 - 我们无法在相同的条件下运行你的代码。



最可能的原因是项目不包含名为ID的元素，因此返回空值。

if a is null, you will get the error.
if a is a value, but a.b is null, you will get the error.
if a.b is a value, but a.b.c is null...

You get the idea.

Put a breakpoint on the line above the one giving the error and use the mouse to hover over each part in turn - find which one is null and you can start looking for why your code has let it be null.

Sorry, but it's over to you and the debugger, I'm afraid - we can't run your code under the same conditions.

The most likely reason is that item does not contain an element called "ID", and so returns a null value.

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