“对象引用未设置为对象的实例”，请参阅下面的代码。 [英] "Object Reference not set to Instance of an object", please see the code below.

问题描述

这是实际的代码，在这里我将获取datagrid的值并通过sql存储过程将其发送到db，所有的帮助表示赞赏。如果有任何错误导致错误，请告诉我

This is the actual code and in this I am taking the values of the datagrid and sending it to the db through a sql stored proc, all the help appreciated. Please let me know if anything wrong in this that is causing the error

Private Sub BtnSendToGP_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtnSendToGP.Click
 
        Dim VarItemNumber As String
         Dim VarItemDescription As String
         Dim VarUnitOfMeasure As String
         Dim VarItemClass As String
         Dim VarCurrentCost As String
         Dim Conn As SqlConnection
 

        Conn = New SqlConnection("Server = db02; Initial Catalog=SDPRD; User=xx; Password=xxxx" & "Data Source=Dynamics;Integrated Security=SSPI;")
         Try
             For cn As Integer = 0 To DtGridView.RowCount - 1
                 VarItemNumber = DtGridView(0, cn).Value.ToString
                 VarItemDescription = DtGridView(3, cn).Value.ToString
                 VarUnitOfMeasure = DtGridView(4, cn).Value.ToString
                 VarItemClass = DtGridView(5, cn).Value.ToString
                 VarCurrentCost = DtGridView(6, cn).Value.ToString
 
                Dim myCommand As SqlCommand = New SqlCommand("dbo.taUpdateCreateItemRcd", Conn)
                 If Conn.State = ConnectionState.Open Then Conn.Close()
                 Conn.Open()
                 myCommand.CommandType = Data.CommandType.StoredProcedure
                 myCommand.Parameters.AddWithValue("@I_vITEMNMBR", VarItemNumber)
                 myCommand.Parameters.AddWithValue("@I_vUseItemClass", 1)
                 myCommand.Parameters.AddWithValue("@I_vITEMDESC", VarItemDescription)
                 myCommand.Parameters.AddWithValue("@I_vUOMSCHDL", VarUnitOfMeasure)
                 myCommand.Parameters.AddWithValue("@I_vITMCLSCD", VarItemClass)
                 myCommand.Parameters.AddWithValue("@I_vCURRCOST", VarCurrentCost)
                 myCommand.Parameters.AddWithValue("@O_iErrorState", 0)
                 myCommand.Parameters.AddWithValue("@oErrString", 0)
                 myCommand.ExecuteNonQuery()
             Next
         Catch ex As Exception
             MsgBox(ex.ToString)
         Finally
             If Conn.State = ConnectionState.Open Then
                 Conn.Close()
             End If
         End Try
         MsgBox("All The Records Added To GP Successfully...", MsgBoxStyle.Information)
     End Sub

推荐答案

堆栈跟踪中应该有更多。



根据以上代码，最易受影响的行是：

There should be more in the stack trace.

Based on above code, most susceptible lines are:

VarItemNumber = DtGridView(0, cn).Value.ToString
VarItemDescription = DtGridView(3, cn).Value.ToString
VarUnitOfMeasure = DtGridView(4, cn).Value.ToString
VarItemClass = DtGridView(5, cn).Value.ToString
VarCurrentCost = DtGridView(6, cn).Value.ToString

对象引用未设置为对象的实例：当您尝试使用属性或调用方法时，会发生此错误对象为null。更多细节：此处 [ ^ ]



Visual Studio DEBUGGER的简单使用可以告诉你对象因为它正在发生。只需查看堆栈跟踪并将调试器放在该行上即可。检查该行的对象，看看是否有任何一个为null，并且您正在尝试使用该对象属性。处理相同。





BTW，为什么在上面的任何代码行中ToString之后没有括号，比如 x.ToString（），请参阅： MSDN：Object.ToString方法 [ ^ ]

Object reference not set to an instance of an object: This error happens when you try to use a property or call a method of an object that is null. More details: here[^]

A simple use of Visual studio DEBUGGER can tell you the object because of which it is happening. Just look at the stack trace and put a debugger on that line. Check the objects of that line and see if any one is null and you are trying to use that objects property. Handle the same.


BTW, why there are no brackets after ToString in any of the code lines above, like x.ToString(), Refer: MSDN: Object.ToString Method [^]

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 是最好的（在大多数情况下）：

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



祝你好运，

-SA

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

嗨谢尔盖，



我们可以使用下面的语法摆脱最后一栏。



DtGridView.AllowUserToAddRows = False



非常感谢您的帮助。

Hi Sergey,

We can get rid of the last column by using the syntax below.

DtGridView.AllowUserToAddRows = False

Thanks a lot for all your help.

这篇关于“对象引用未设置为对象的实例”，请参阅下面的代码。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！