对象引用未设置为对象的实例。 [英] Object reference not set to an instance of the object.

问题描述

您好！我有代码：

Hello! I have code:

Public ImageList As ArrayList
    Dim strFileSize As String = ""
    Dim path As String = "c:\catalog_images\"
    Dim di As New IO.DirectoryInfo(Path)
    Dim aryFi As IO.FileInfo() = di.GetFiles("*.png")
    Dim fi As IO.FileInfo
    Dim counter As Integer = 1

在构造函数Sub New中：

And in constructor Sub New have:

ImageList = Nothing
       For Each Me.fi In aryFi
           ImageList.Add(fi.FullName)
       Next

但是调用错误对象引用未设置为对象的实例。

有什么问题？

But calls error "Object reference not set to an instance of the object."
What is wrong?

推荐答案

你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：确保将成员/变量正确初始化为非空引用，或者将其检查为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 [ ^ ]。







评论后我可以看到你的错误：你将引用 ImageList 分配给Nothing（在VB.NET中为Null），然后尝试通过调用 ImageList.Add 取消引用它。就是这样。



（我希望这只是一个错字;故意这样做意味着一般都不会对编程有任何线索。）



（这表明你对你正在做的事情一无所知;所以没有什么可以帮助你，除非你坐下来学习一些编程的基础知识


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: wither 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"[^].



After you comment I can see one you bug: you assign the reference ImageList to Nothing (which is Null, in VB.NET), and later attempt to dereference it by calling ImageList.Add. That''s it.

(I hope it''s just a typo; doing it intentionally would mean having no clue in programming in general.)

(which shows that you don''t have a clue on what you are doing; so nothing can help you, unless you sit down to learn some basics of prog

Good luck,

—SA

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