Using Try/Catch block to set file path? - visual-studio

Question

I'm having a bit of trouble figuring out an assignment for my Visual Basic course. I am told to assume that a given text file is not in the \bin\Debug folder of my program, so I am trying to throw an exception error and get the correct path from the user via an inputbox but nothing appears to happen, or the variable isn't being set, I'm not entirely sure which. I have my code below, any hints as to why this will not work for me?
Thanks!
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

Answer 1

Your inner Try/Catch block should be inside the FileNotFoundException catch.
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
An even better solution would be...
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
This will first check if the file exists, and continue looping until the user enter ones that does. This allows you to remove the FileNotFoundException catch.
This also uses Integer.TryParse to check if the value was casted correctly, allowing you to remove the InvalidCastException catch.
Lastly, opening the reader with a Using statement eliminates the need for a finally/nested try-catch block, as Using implements this internally.

Answer 2

I would bet that the exception being thrown is not an IO.FileNotFoundException, so your InputBox code is never being hit. OpenText can throw quite a few types of exception. There are several ways you can go about doing this without an exception (File.Exists comes to mind), but to continue on this route I would change your exception handling to something like this:
Catch exc as Exception
If TypeOf exc Is InvalidCastException Then
'...
Else
path = InputBox(....)
End If
End Try