VB 2010“变量”未声明。由于其保护级别，可能无法访问 [英] VB 2010 'variable' is not declared. It may be inaccessible due to it's protection level
问题描述
我有点类似于VB，并且想知道如何在多个Subs中使用变量。这只是一个熟悉VB的测试应用。
我的代码：
i'm sort of a n00b to VB and was wondering how to make a variable available across multiple Subs. It's just a test app to get familiar with VB. My Code:
Public Class Sentences
Private Sub SentenceBox_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles SentenceBox.TextChanged
If Me.Text = Trim(Sentence) Then
MsgBox("Good job!")
Main_Menu.Show()
Me.Close()
End If
End Sub
Private Sub ABCs_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Dim random As Integer = CInt((Rnd() * 10) + 1)
Dim Sentence As String
Select Case random
Case 1
Sentence = "The quick brown fox jumped over the lazy dog!"
Case 2
Sentence = "Hi there, how are you doing?"
Case 3
Sentence = "What is the answer to life?"
Case 4
Sentence = "The cat in the hat was fat."
Case 5
Sentence = "John and Sam had always been fat."
Case 6
Sentence = "The snow is falling hard."
Case 7
Sentence = "Here, dinner is always served nightly."
Case 8
Sentence = "The dog barks at the passing cars."
Case 9
Sentence = "The dust settles on the books."
Case 10
Sentence = "Fire burns brightly when you add kerosene."
End Select
End Sub
Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
SentenceBox.Text = Sentence
End Sub
End Class
我的错误是：
未声明句子。由于其保护级别，它可能是可访问的。
"Sentences" is not declared. It may be in accessable due to it's protection level."
推荐答案
VB.NET中的变量具有非常特殊的范围，将它们的可用性限制为代码的各个部分
Variables in VB.NET have a very particular scope, limiting their availability to various portions of your code depending on how and where they are declared.
您的句子变量具有过程级范围，该范围意味着它仅在声明它的过程中可用。对于您而言，它是在 ABCs_Load 方法（ Sub）中声明的，因此
Your Sentence variable has procedure-level scope, which means that it is available only within the procedure in which it was declared. In your case, it's declared in the ABCs_Load method ("Sub"), so it will only be available to code within that method.
相反，如果您想访问句子
If, instead, you want to be able to access the Sentence variable in any of the methods in your class (Forms are always classes in VB.NET), you can declare the variable with Module-level scope. To do this, you need to add a private field to your Sentences class, outside of any particular method (Sub or Function). This declaration will look something like this:
Private Sentence As String
当然，您也可以将变量声明为 Public 而不是 Private ，这将使其可用于当前课程之外的其他课程。例如，如果您有一个 second 表单，希望能够访问 Sentence 变量的内容，则可以将其声明为公共在第一个表单的类中，然后从 second 表单的类中的一个方法访问它，如下所示：
Of course, you can also declare the variable as Public instead of Private, which will make it available to other classes outside of the current class. For example, if you had a second form that you wanted to be able to access the contents of your Sentence variable, you could declare it as Public in the first form's class and then access it from one of the methods in the second form's class like so:
MessageBox.Show(myForm1.Sentence)
请注意，因为它确实位于另一种形式（与正在访问的形式不同的类）之内，所以您必须完全限定对该引用的引用。就像您的家人称呼您为迈克一样，但其他人却不得不称您为迈克·琼斯，以使您与迈克·史密斯区分开。
Notice that because it does lie within another form (a class different than the one it is being accessed in), you have to fully qualify the reference to it. It's like how your family might call you "Mike," but others have to call you "Mike Jones" to differentiate you from "Mike Smith."
要进一步阅读，请参阅MSDN上的以下相关文章：
For further reading, also see these related articles on MSDN:
- Access Levels in Visual Basic
- How to: Control the Scope of a Variable (Visual Basic)
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