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

问题描述

有关调用

实时（JIT）调试而不是此对话框的详细信息，请参阅此消息的结尾。

 **************异常文本************** 
 System.NullReferenceException：对象引用未设置为对象的实例。 
 at crifanLib.getUrlRespHtml（String url，Dictionary`2 headerDict，String charset，Dictionary`2 postDict，Int32 timeout，String postDataStr）
 at crifanLib.getUrlRespHtml（String url，Dictionary`2 headerDict，String charset ，Dictionary`2 postDict，String postDataStr）
 at crifanLib.getUrlRespHtml（String url，Dictionary`2 headerDict，Dictionary`2 postDict）
 at crifanLib.getUrlRespHtml（String url，Dictionary`2 headerDict）
 at SEOBacklinkSoftware.frmSEOBacklinkSoftware.searchAndParse（String searchStr）
 at SEOBacklinkSoftware.frmSEOBacklinkSoftware.btnSearch_Click（Object sender，EventArgs e）
 at System.Windows.Forms.Control.OnClick（EventArgs e）
在System.Windows.Forms.Button.OnClick（EventArgs e）
 at System.Windows.Forms.Button.OnMouseUp（MouseEventArgs mevent）
 at System.Windows.Forms.Control.WmMouseUp（Message& m，MouseButtons按钮，Int32单击）
在System.Windows.Forms.Control.WndProc（消息& m）
a t System.Windows.Forms.ButtonBase.WndProc（Message& m）System.Windows.Fornd.Button.WndProc（消息& m）
在System.Windows上的System.Windows.Forms.Control.ControlNativeWindow.OnMessage（消息& m）
 
 .Forms.Control.ControlNativeWindow.WndProc（Message& m）
 at System.Windows.Forms.NativeWindow.Callback（IntPtr hWnd，Int32 msg，IntPtr wparam，IntPtr lparam）
 
 
 **************已加载程序集************** 
 mscorlib 
汇编版本：2.0.0.0 
 Win32版本：2.0.50727.4927（NetFXspW7.050727-4900）
 CodeBase：file：/// C：/Windows/Microsoft.NET/Framework/v2.0.50727/mscorlib.dll 
 --- ------------------------------------- 
 SEOBacklinkSoftware 
汇编版本：1.0 .0.0 
 Win32版本：1.1.0.0 
 CodeBase：file：/// C：/ Program％20Files％20（x86）/Microsoft/Setup1/SEOBacklinkSoftware.exe 
 ---- ------------------------------------ 
 System.Windows.Forms 
 Assembly版本：2.0.0.0 
 Win32版本：2.0.50727.4927（NetFXspW7.050 727-4900）
 CodeBase：file：/// C：/Windows/assembly/GAC_MSIL/System.Windows.Forms/2.0.0.0__b77a5c561934e089/System.Windows.Forms.dll 
 ---- ------------------------------------ 
 System 
汇编版本：2.0。 0.0 
 Win32版本：2.0.50727.4927（NetFXspW7.050727-4900）
 CodeBase：file：/// C：/Windows/assembly/GAC_MSIL/System/2.0.0.0__b77a5c561934e089/System.dll 
 ---------------------------------------- 
 System.Drawing 
汇编版本：2.0.0.0 
 Win32版本：2.0.50727.4927（NetFXspW7.050727-4900）
 CodeBase：file：/// C：/Windows/assembly/GAC_MSIL/System.Drawing/ 2.0.0.0__b03f5f7f11d50a3a / System.Drawing.dll 
 ------------------------------------ ---- 
 System.Configuration 
汇编版本：2.0.0.0 
 Win32版本：2.0.50727.4927（NetFXspW7.050727-4900）
 CodeBase：file：/// C ：/Windows/assembly/GAC_MSIL/System.Configuration/2.0.0.0__b03f5f7f11d50a3a/System.Configuration.dll 
 ----------------------- ----------------- 
 System.Xml 
汇编版本：2.0.0.0 
 Win32版本：2.0.50727.4927（NetFXspW7.050727-4900 ）
 CodeBase：file：/// C：/Windows/assembly/GAC_MSIL/System.Xml/2.0.0.0__b77a5c561934e089/System.Xml.dll 
 ----------- ----------------------------- 
 HtmlAgilityPack 
汇编版本：1.4.6.0 
 Win32版本：1.4.6.0 
 CodeBase：file：/// C：/ Program％20Files％20（x86）/Microsoft/Setup1/HtmlAgilityPack.DLL 
 ------------ ---------------------------- 
 System.Web 
汇编版本：2.0.0.0 
 Win32版本：2.0.50727.4927（NetFXspW7.050727-4900）
 CodeBase：file：/// C：/Windows/assembly/GAC_32/System.Web/2.0.0.0__b03f5f7f11d50a3a/System.Web.dll 
 ---------------------------------------- 
 
 ** ************ JIT调试************** 
要启用实时（JIT）调试，请使用.config文件
应用程序或计算机（machine.config）必须在sy中设置
 jitDebugging值stem.windows.forms部分。 
应用程序也必须在启用调试
的情况下编译。 
 
例如：
 
< configuration> 
< system.windows.forms jitdebugging =true/> 
< / configuration> 

启用JIT调试后，任何未处理的异常

将被发送到计算机上注册的JIT调试器

而不是由此对话框处理。

解决方案

这是c中最常见的错误。

当你尝试时会出现访问一个空的Object的成员



尝试追踪错误



Keep Break Point在你获得Null引用错误的行



每当你试图访问一个对象时添加以下条件

 对象 anyobject; 
 
  if （anyobject！=  null ）
 {
 anyobject.Property; 
 anyobject.Method（）; 
} 

有用的链接主题：

http://www.dotnetperls.com/nullreferenceexception [ ^ ]

http://stackoverflow.com/questions/1943465/avoiding-null-reference-exceptions [ ^ ]

http://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-and-how-do-i-fix-it [ ^ ]

您没有显示带有对象引用未设置为对象实例消息的异常位置。



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 [ ^ ]。



祝你好运，

-SA

参考最受欢迎的答案由Sergey 对象参考未设置为对象的实例，请参阅下面的代码。 [< a href =http://www.codeproject.com/Answers/585918/22ObjectplusReferenceplusnotplussetplustoplusInsta#answer1target =_ blanktitle =New Window> ^ ]。

See the end of this message for details on invoking
just-in-time (JIT) debugging instead of this dialog box.

************** Exception Text **************
System.NullReferenceException: Object reference not set to an instance of an object.
   at crifanLib.getUrlRespHtml(String url, Dictionary`2 headerDict, String charset, Dictionary`2 postDict, Int32 timeout, String postDataStr)
   at crifanLib.getUrlRespHtml(String url, Dictionary`2 headerDict, String charset, Dictionary`2 postDict, String postDataStr)
   at crifanLib.getUrlRespHtml(String url, Dictionary`2 headerDict, Dictionary`2 postDict)
   at crifanLib.getUrlRespHtml(String url, Dictionary`2 headerDict)
   at SEOBacklinkSoftware.frmSEOBacklinkSoftware.searchAndParse(String searchStr)
   at SEOBacklinkSoftware.frmSEOBacklinkSoftware.btnSearch_Click(Object sender, EventArgs e)
   at System.Windows.Forms.Control.OnClick(EventArgs e)
   at System.Windows.Forms.Button.OnClick(EventArgs e)
   at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
   at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at System.Windows.Forms.ButtonBase.WndProc(Message& m)
   at System.Windows.Forms.Button.WndProc(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)


************** Loaded Assemblies **************
mscorlib
    Assembly Version: 2.0.0.0
    Win32 Version: 2.0.50727.4927 (NetFXspW7.050727-4900)
    CodeBase: file:///C:/Windows/Microsoft.NET/Framework/v2.0.50727/mscorlib.dll
----------------------------------------
SEOBacklinkSoftware
    Assembly Version: 1.0.0.0
    Win32 Version: 1.1.0.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Microsoft/Setup1/SEOBacklinkSoftware.exe
----------------------------------------
System.Windows.Forms
    Assembly Version: 2.0.0.0
    Win32 Version: 2.0.50727.4927 (NetFXspW7.050727-4900)
    CodeBase: file:///C:/Windows/assembly/GAC_MSIL/System.Windows.Forms/2.0.0.0__b77a5c561934e089/System.Windows.Forms.dll
----------------------------------------
System
    Assembly Version: 2.0.0.0
    Win32 Version: 2.0.50727.4927 (NetFXspW7.050727-4900)
    CodeBase: file:///C:/Windows/assembly/GAC_MSIL/System/2.0.0.0__b77a5c561934e089/System.dll
----------------------------------------
System.Drawing
    Assembly Version: 2.0.0.0
    Win32 Version: 2.0.50727.4927 (NetFXspW7.050727-4900)
    CodeBase: file:///C:/Windows/assembly/GAC_MSIL/System.Drawing/2.0.0.0__b03f5f7f11d50a3a/System.Drawing.dll
----------------------------------------
System.Configuration
    Assembly Version: 2.0.0.0
    Win32 Version: 2.0.50727.4927 (NetFXspW7.050727-4900)
    CodeBase: file:///C:/Windows/assembly/GAC_MSIL/System.Configuration/2.0.0.0__b03f5f7f11d50a3a/System.Configuration.dll
----------------------------------------
System.Xml
    Assembly Version: 2.0.0.0
    Win32 Version: 2.0.50727.4927 (NetFXspW7.050727-4900)
    CodeBase: file:///C:/Windows/assembly/GAC_MSIL/System.Xml/2.0.0.0__b77a5c561934e089/System.Xml.dll
----------------------------------------
HtmlAgilityPack
    Assembly Version: 1.4.6.0
    Win32 Version: 1.4.6.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Microsoft/Setup1/HtmlAgilityPack.DLL
----------------------------------------
System.Web
    Assembly Version: 2.0.0.0
    Win32 Version: 2.0.50727.4927 (NetFXspW7.050727-4900)
    CodeBase: file:///C:/Windows/assembly/GAC_32/System.Web/2.0.0.0__b03f5f7f11d50a3a/System.Web.dll
----------------------------------------

************** JIT Debugging **************
To enable just-in-time (JIT) debugging, the .config file for this
application or computer (machine.config) must have the
jitDebugging value set in the system.windows.forms section.
The application must also be compiled with debugging
enabled.

For example:

<configuration>
    <system.windows.forms jitdebugging="true" />
</configuration>

When JIT debugging is enabled, any unhandled exception
will be sent to the JIT debugger registered on the computer
rather than be handled by this dialog box.

解决方案

This is the most common error in c#
It will arise when you try to access the members of an Object which is null

Try to trace the error

Keep Break Point at the line you are getting the Null Reference error

add the below condition whenever you are trying to access an object

Object anyobject ;

if( anyobject != null )
{
  anyobject.Property;
anyobject.Method();
}

helpful links on the topic:
http://www.dotnetperls.com/nullreferenceexception[^]
http://stackoverflow.com/questions/1943465/avoiding-null-reference-exceptions[^]
http://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-and-how-do-i-fix-it[^]

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

Refer the most popular answer by Sergey "Object Reference not set to Instance of an object", please see the code below.[^].

这篇关于你调用的对象是空的。在c＃中的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！