Exception classes for file I/O in VB.NET
In this article we will handle the exceptions that occur during the I/O operations.
Most of the time, you can write code to avoid the Exceptions that can occur when you perform I/O operations. For example, you can avoid a DirectoryNotFoundException by using the Exists method of the Directory class to be sure that the directory exists before you try to use it in the file path for a new file stream.
When handling I/O exceptions, it's common to use a Finally block. In this block, it's common to use the stream's Close method to close all the streams that are open. This frees the resources that are used to access the stream. To start, the statement just before the Try block declare a variable for the stream. That way, this variable is available to the Catch blocks and the Finally block.
Code that uses exception classes
Dim dirpath As String = "c:\VB 2008\Files\"
Dim filepath As String = dirpath & "products.txt"
Dim fs As FileStream
fs = New FileStream(filepath, FileMode.Open)
Catch ex As FileNotFoundException
MessageBox.Show(filepath & "not found.", "file not found")
Catch ex As DirectoryNotFoundException
MessageBox.Show(dirpath & "not found.", "directory not found")
Catch ex As IOException
MessageBox.Show(ex.Message, "IO Exception")
If fs IsNot Nothing Then
A dialog box appears as output and displays the error message: