In visual basic, the try-catch-finally statement is useful to handle unexpected or runtime exceptions which will occur during execution of the program.
In try-catch-finally statement, the Try block is used to hold the code that may cause an exception, Catch block to handle exceptions and the Finally block is used to clean up or release any resources that are allocated in a Try block. For example, close database connections or any streams or files that are opened in Try block.
In visual basic, the finally block will always come after Try or Catch blocks and the Finally block will always execute even if an exception occurred or not and it is useful to clean up or dispose of unmanaged objects based on the requirements.
Following is the syntax of handling errors in visual basic using Try-Catch-Finally statement.
Try
' Code that may cause exception
Catch ex As Exception
' Exception handling
Finally
' Cleanup resources
End Try
As per the above syntax, the Try block will contain the guarded code that may cause an exception so that if any errors occurred in our code, then immediately the code execution will be moved to Catch block to handle those exceptions.
After completion of Try or Try & Catch blocks, the Finally block will always be executed even if an exception occurred or not and it is useful to clean up or release unmanaged resources.
In Try-Catch-Finally statement, only one Try & Finally blocks are allowed but, we can use multiple catch blocks to handle different exception types.
Following is the example of handling exceptions in visual basic using Try-Catch-Finally statement.
Imports System.IO
Module Module1
Sub Main(ByVal args As String())
Dim fpath As String = "D:\Test.txt"
Dim sr As StreamReader = New StreamReader(fpath)
Try
Dim txt As String
While txt IsNot Nothing
Console.WriteLine(txt)
End While
Catch ex As Exception
Console.WriteLine("Exception: {0}", ex.Message)
Finally
If sr IsNot Nothing Then
sr.Close()
End If
End Try
Console.ReadLine()
End Sub
End Module
If you observe the above code, we used Try, Catch and Finally blocks to handle runtime or unexpected errors during execution of the program. Here, we wrote a code that may throw an exception inside of Try block and in Catch block we are handling the exception. As discussed, the Finally block will execute after completion of Try or Catch block execution and release the required resources.
This is how we can use Try-Catch-Finally blocks to handle unexpected or runtime exceptions based on our requirements.