“对象引用未设置为对象的实例”的错误。 [英] Error of "Object reference not set to an instance of an object."

问题描述

伙计们，

我收到了错误的主题提及。

i使用断点来检查它。数据表中有数据。

但是当来到 rptDoc.SetDataSource（dt）行时，则会发生错误。

所以有人知道如何解决这个问题吗？或者给我如此指导如何找出主要问题。

提前致谢。以下是我的编码。

Hi guys,
I getting the error as the subject mention.
i used breakpoints to check it.There have data come out in datatable.
But when come to line rptDoc.SetDataSource(dt) then the error occur.
So have anyone got idea how to solve this? Or give me so guide how to find out the main problem.
Thanks in advance. Below is my coding.

If Not ConnectDB(Conn, g_Conn) Then Exit Sub
Console.WriteLine(SQLLossOver)
Dim s As String = SQLLossOver.ToString
Dim dt As New DataTable
da = New OdbcDataAdapter(SQLLossOver.ToString, Conn)
da.Fill(dt)
rptDoc.SetDataSource(dt)

推荐答案

至少有一个bug是明显的：你声明 dt 但从不初始化它。 （这是一个VB.NET缺陷，在C＃中，这样的东西不能编译。）



你不需要问这样的问题。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 [ ^ ]。



祝你好运，

-SA

At least one bug is apparent: you declare dt but never initialize it. (This is a VB.NET defect, in C#, such thing would not compile.)

You don''t need to ask such questions. 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"[^].

Good luck,

—SA

查看您的代码。在将数据表用作报表的数据源之前，需要填充数据表（ dt ）。



读取这个： http://codebetter.com/raymondlewallen/2005/06/23/system-nullreferenceexception-object-reference-not-set-to-an-instance-of-an-object -3-common-cause-in-vb-net / [ ^ ]

Have a look at your code. You need to fill datatable (dt), before you use it as a datasource of your report.

Read this: http://codebetter.com/raymondlewallen/2005/06/23/system-nullreferenceexception-object-reference-not-set-to-an-instance-of-an-object-3-common-causes-in-vb-net/[^]

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