vb.net Visual Basic：未将对象引用设置为对象的实例
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visual basic: object reference not set to an instance of an object
提问by okojie ernest
i watched a video tutorial and saw the guy write and execute the code below and worked but when i try to compile mine it says "object reference not set to an instance of an object". i have tried several things to see if i can get what the problem is but to no avail.
我观看了一个视频教程，看到这个人编写并执行下面的代码并工作，但是当我尝试编译我的代码时，它说“对象引用未设置为对象的实例”。我已经尝试了几件事，看看我是否能找到问题所在，但无济于事。
Imports System.IO
Public Class Form2
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Try
Dim myline = New StreamReader("TextFile1.txt")
Dim line As String = ""
While Not IsNothing(line)
line = myline.ReadLine
If IsNothing(line) Then
TextBox2.AppendText(line)
End If
End While
myline.Close()
Catch ex As Exception
TextBox2.AppendText(ex.Message)
MsgBox(ex.Message)
End Try
End Sub
End Class
can anyone help please? thanks
有人可以帮忙吗？谢谢
回答by Markus
I think you are missing a Not:
我认为你缺少一个Not：
If Not IsNothing(line) Then
TextBox2.AppendText(line)
End If
回答by ??ssa P?ngj?rdenlarp
this kind of "If Not IsNothing:" is strange kind of.
this kind of "If Not IsNothing:" is strange kind of.
IsNothingis a VB-ism as opposed to NET syntax. Other ways of coding it include:
IsNothing是一种 VB 主义，而不是 NET 语法。其他编码方式包括：
If String(line).IsNullOrEmpty = False Then
' or
If Not String(line).IsNullOrEmpty Then
' which is the same type of garble as Not IsNothing
also:
If Line IsNot Nothing Then
Since IsNothingis a VB function returning a Boolean, you can also just evaluate it:
由于IsNothing是返回布尔值的 VB 函数，您也可以对其进行评估：
If IsNothing(line) = False Then ...
回答by Raheel Khan
In the condition If IsNothing(line) Thenyou are missing a Not.
在If IsNothing(line) Then您缺少Not.
If Not IsNothing(line) Then
TextBox2.AppendText(line)
End If
回答by TheVolatileChemist
Well, it's simple enough :) Just missing your object definition :)
嗯，这很简单:) 只是缺少您的对象定义:)
Dim myline = New StreamReader("TextFile1.txt")
-doesnt define myline. It's like your doing this:
- 没有定义 myline。这就像你这样做：
Dim variable = 1
You have to say:
你不得不说：
Dim myline as StreamReader = New StreamReader("TextFile1.txt")
So that Visual Basic knows what kind of variable you're making before you stuff it with a value. There are better, more acute ways of reading files in VB.NET (Personally my favorite language :) ), but I'm sure this will do for your application.
这样 Visual Basic 就知道在用值填充变量之前要创建什么样的变量。在 VB.NET（我个人最喜欢的语言:)）中有更好、更敏锐的读取文件的方法，但我相信这对您的应用程序有用。
If you end up wanting to read an entire file to an array (list), you can look through snippets to find the code for reading a file to a string, then split it to a list with the anystring.split command and the "vbCRLF" character (An endline, like your enter button).
如果您最终想要将整个文件读取到数组（列表）中，您可以查看片段以找到将文件读取为字符串的代码，然后使用 anystring.split 命令和“vbCRLF”将其拆分为列表" 字符（结束线，就像您的输入按钮）。
回答by Chris Dunaway
Seems like it would be easier to just call the ReadAllText method:
似乎只调用 ReadAllText 方法会更容易：
Imports System.IO
Public Class Form2
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Try
TextBox2.AppendText(File.ReadAllText("TextFile1.txt"))
Catch ex As Exception
TextBox2.AppendText(ex.Message)
MsgBox(ex.Message)
End Try
End Sub
End Class
