Visual studio 是否使用Try/Catch块设置文件路径？

我在计算Visual Basic课程的作业时遇到了一些困难。我被告知假定给定的文本文件不在程序的\bin\Debug文件夹中，因此我试图抛出一个异常错误，并通过inputbox从用户那里获取正确的路径，但似乎什么也没有发生，或者变量没有设置，我不完全确定是哪个。我在下面有我的代码，关于为什么这对我不起作用有什么提示吗

谢谢

Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load

    Dim sr As IO.StreamReader
    Dim age As Integer
    Dim path As String
    Try
        sr = IO.File.OpenText("Ages.txt")
        age = CInt(sr.ReadLine)
        txtOutput.Text = "Age is " & age
    Catch exc As IO.FileNotFoundException
        path = InputBox("File Ages.txt not found." & vbCrLf & "Please enter the correct path to the file.", _
                 "Example: C:\Documents\My Text Files")
    Catch exc As InvalidCastException
        MessageBox.Show("File 'Ages.txt' contains an invalid age.", "Warning!")

        Try
            sr = IO.File.OpenText(path)
        Finally
            txtOutput.Text = "Age is " & age
        End Try
    Finally
        Try
            sr.Close()
        Catch

        End Try
    End Try

End Sub

---

内部Try/Catch块应位于FileNotFoundException捕获内

Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
    Dim sr As IO.StreamReader
    Dim age As Integer
    Dim path As String

    Try
        sr = IO.File.OpenText("Ages.txt")
        age = CInt(sr.ReadLine)
        txtOutput.Text = "Age is " & age
    Catch exc As IO.FileNotFoundException
        path = InputBox("File Ages.txt not found." & vbCrLf & "Please enter the correct path to the file.", _
                 "Example: C:\Documents\My Text Files")
        Try
            sr = IO.File.OpenText(path)
        Finally
            txtOutput.Text = "Age is " & age
        End Try
    Catch exc As InvalidCastException
        MessageBox.Show("File 'Ages.txt' contains an invalid age.", "Warning!")
    Finally
        Try
            sr.Close()
        Catch

        End Try
    End Try
End Sub

更好的解决办法是

Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load

    Dim age As Integer
    Dim path As String = "Ages.txt"
    Dim fileFound As Boolean = False

    While Not IO.File.Exists(path)
        path = InputBox("File Ages.txt not found." & vbCrLf & "Please enter the correct path to the file.", _
                     "Example: C:\Documents\My Text Files")
    End While

    Using sr As IO.StreamReader = IO.File.OpenText(path)
        If Integer.TryParse(sr.ReadLine, age) Then
            txtOutput.Text = "Age is " & age
        Else
            MessageBox.Show("File 'Ages.txt' contains an invalid age.", "Warning!")
        End If
    End Using

End Sub

这将首先检查文件是否存在，并继续循环，直到用户输入存在的文件。这允许您删除FileNotFoundException捕获

Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
    Dim sr As IO.StreamReader
    Dim age As Integer
    Dim path As String

    Try
        sr = IO.File.OpenText("Ages.txt")
        age = CInt(sr.ReadLine)
        txtOutput.Text = "Age is " & age
    Catch exc As IO.FileNotFoundException
        path = InputBox("File Ages.txt not found." & vbCrLf & "Please enter the correct path to the file.", _
                 "Example: C:\Documents\My Text Files")
        Try
            sr = IO.File.OpenText(path)
        Finally
            txtOutput.Text = "Age is " & age
        End Try
    Catch exc As InvalidCastException
        MessageBox.Show("File 'Ages.txt' contains an invalid age.", "Warning!")
    Finally
        Try
            sr.Close()
        Catch

        End Try
    End Try
End Sub

这还使用Integer.TryParse检查值是否正确强制转换，从而允许您删除InvalidCastException捕获

---

最后，使用Using语句打开读卡器消除了对finally/nestedtry-catch块的需要，因为Using在内部实现了这一点

我敢打赌抛出的异常不是一个

IO.FileNotFoundException

，因此您的

输入框

代码永远不会被命中。可以引发很多类型的异常。有几种方法可以毫无例外地执行此操作（我想到），但要继续此过程，我会将您的异常处理更改为以下内容：

Catch exc as Exception
    If TypeOf exc Is InvalidCastException Then
        '...
    Else
        path = InputBox(....)
    End If
End Try

---

当你说什么都没有发生时，你是说输入框没有被显示吗？