[VB.NET]未将对象引用设置为对象的实例
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[VB.NET]Object reference not set to an instance of an object
提问by Zebriukas Dry?iukas
I'm trying to add value of column from selected row on my datagridview to Collection(but I get same error if I do it with List or Array)
我正在尝试将 datagridview 上选定行的列值添加到 Collection（但如果我使用 List 或 Array 执行此操作，则会出现相同的错误）
CODE:
代码：
Dim zdgv = MyDataGridView
For a = 0 To zdgv.SelectedRows.Count - 1
MsgBox(zdgv.Rows(zdgv.SelectedRows(a).Index).Cells(0).Value.ToString)
Try
MyCollection.Add(zdgv.Rows(zdgv.SelectedRows(a).Index).Cells(0).Value.ToString)
Catch ex As Exception
MsgBox(ex.Message)
MsgBox(ex.InnerException)
End Try
Next
ex.Message = Object reference not set to an instance of an object
ex.InnerException = empty
ex.InnerException.Message = Makes program crash, goes to code screen, highlights MsgBox(ex.InnerException)line, and gives error: Object reference not set to an instance of an object
ex.Message =未将对象引用设置为对象的实例
ex.InnerException =空
ex.InnerException.Message = 使程序崩溃，转到代码屏幕，突出显示MsgBox(ex.InnerException)行，并给出错误：未将对象引用设置为对象的实例
ADDITIONAL INFO:Using QuickWatch on zdgv gives me all info. Using it on Rows after it(zdgv) says: 'Rows' is not declared. It may be inaccessible due to its protection level.
附加信息：在zdgv 上使用 QuickWatch 为我提供了所有信息。在 it(zdgv) 之后在 Rows 上使用它说：'Rows' 未声明。由于其保护级别，它可能无法访问。
P.S. Yes I've googled, but none problem was similar. Yes I've searched here but no info. I've tryed r/visualbasic too - nothing... I've even tryed search for c# related stuff with this error - nothing. :/
PS 是的，我用谷歌搜索过，但没有类似的问题。是的，我在这里搜索过，但没有信息。我也尝试过 r/visualbasic - 什么都没有......我什至尝试搜索与此错误相关的 c# 相关内容 - 什么都没有。：/
Thanks in advance.
提前致谢。
EDIT1:I've tryed make non-databound datagridview in new project, and add one value from it to collection - same error. I guess I should go google about "Setting Reference of Object to an Instance of an Object".
EDIT1：我已经尝试在新项目中创建非数据绑定 datagridview，并将其中的一个值添加到集合中 - 同样的错误。我想我应该去谷歌一下“将对象的引用设置为对象的实例”。
EDIT2:This one was fail - newbie mistake.
EDIT2：这是失败 - 新手错误。
EDIT3:using quickwatch on
EDIT3：使用 quickwatch
zdgv.Rows(zdgv.SelectedRows(a).Index).Cells(0).Value.ToString
it shows right value(correct one, without throwing errors) = "1".
它显示正确的值（正确的一个，没有抛出错误）=“1”。
采纳答案by Matt B-L
This code works like a charm on my side.
这段代码对我来说就像一个魅力。
Did you forget a New on your MyCollection?
您是否忘记了 MyCollection 上的 New？
Dim zdgv = MyDataGridView
Dim MyCollection As New Collection
For a = 0 To zdgv.SelectedRows.Count - 1
MsgBox(zdgv.Rows(zdgv.SelectedRows(a).Index).Cells(0).Value.ToString)
Try
MyCollection.Add(zdgv.Rows(zdgv.SelectedRows(a).Index).Cells(0).Value.ToString)
Catch ex As Exception
MsgBox(ex.Message)
If ex.InnerException IsNot Nothing Then
MsgBox(ex.InnerException)
End If
End Try
Next
回答by Chris
At top of code - just below public class classname and above first sub I've this: Public XXXXX As Collection
在代码顶部 - 就在公共类类名下方和第一个子类上方我有这个：Public XXXXX As Collection
You don't' create an instance of collectionand then you try add some items to it.
您不会创建一个实例，collection然后尝试向其中添加一些项目。
It should be:
它应该是：
Public XXXXX As New Collection
Public XXXXX As New Collection
Or you need to create a new instance somewhere else before access it
或者您需要在其他地方创建一个新实例才能访问它
XXXXX = New Collection
XXXXX = New Collection
回答by Matt B-L
ex.InnerException is null, and you try to access is Message attribute. It's a normal behavior. You should try something like
ex.InnerException 为 null，而您尝试访问的是 Message 属性。这是正常的行为。你应该尝试像
Try
MyCollection.Add(zdgv.Rows(zdgv.SelectedRows(a).Index).Cells(0).Value.ToString)
Catch ex As Exception
MsgBox(ex.Message)
If ex.InnerException IsNot Nothing Then
MsgBox(ex.InnerException)
End if
End Try
InnerException is not null only if a sub method threw an exception under it.
只有当子方法在其下抛出异常时，InnerException 才不为 null。
回答by Steev Ba
Best Solution I foundBasically the error is that your code is making use of a non-existing row.
我发现的最佳解决方案基本上错误是您的代码正在使用不存在的行。
You will merely need to turn to false the datagridview "AllowUserToAddRows" property. Then all your normal loops will work properly.
您只需要将 datagridview 的“AllowUserToAddRows”属性设为 false。然后你所有的正常循环都会正常工作。
Dim zdgv = DataGridView1
For Each row As DataGridViewRow In zdgv.Rows
ListBox2.Items.Add(row.Cells(1).Value.ToString)
Next
or
或者
for i as integer = 0 to datagridView1.rows.count - 2
'enter code here
Next
MK :)
MK :)
