Recovering an Exception using ASP.NET 2.0 and VB .NET

This tutorial will show you how to recover an exception using ASP.NET 2.0 and VB.NET

There are many ways to re-try a try block in .NET. Here is one simple solution to this problem.

In this example we will be catching an exception when trying to create a directory in the filesystem, so we will need the System.IO namespace. Our code will catch an exception if the user tries to create a directory that is 248 characters long.

Imports System.IO

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We'll put our code in the btnSubmit_Click() event.

When the btnSubmit_Click() event fires it runs a try block. The try block attempts to create the directory given in the textbox. In this example, we are specifying that our catch blocks handles exceptions of the type PathTooLongException. When this exception is raised, we truncate the given path to one less character and follows a goto statement to the start_try label. Labels are used as markers in different areas of code. The try block will continue to try its code until the directory has been successfully created.

Protected Sub btnSubmit_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnSubmit.Click start_try: Try Directory.CreateDirectory(MapPath(".") & "\" & txtDir.Text) Catch ex As PathTooLongException lblStatus.Text = "There was an PathTooLongException when creating the directory" lblStatus.Text &= " in " & MapPath(".") & "\" & Constants.vbCr & "..." 'remove one character txtDir.Text = txtDir.Text.Substring(0, txtDir.Text.Length - 1) lblStatus.Text &= "Truncated Directory Name..." & Constants.vbCr GoTo start_try 'and try again Catch ex As Exception lblStatus.Text = ex.Message End Try lblStatus.Text &= "Directory successfully created!" & Constants.vbCr End Sub

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We have one textbox, a Submit button, and a label on the front end for user interaction. The front end .aspx page looks something like this:

<table width="600" border="0" align="center" cellpadding="5" cellspacing="1" bgcolor="#cccccc"> <tr> <td width="100" align="right" bgcolor="#eeeeee" class="header1"> Catching an Exception:</td> <td align="center" bgcolor="#FFFFFF"> Directory:<asp:TextBox ID="txtDir" runat="server"></asp:TextBox> <br /> <asp:Button ID="btnSubmit" runat="server" Text="Submit" OnClick="btnSubmit_Click" /><br /> &nbsp;<asp:label ID="lblStatus" runat="server"></asp:label></td> </tr> </table>

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The flow for the code behind page is as follows.

Imports System.IO Partial Class _Default Inherits System.Web.UI.Page Protected Sub btnSubmit_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnSubmit.Click start_try: Try Directory.CreateDirectory(MapPath(".") & "\" & txtDir.Text) Catch ex As PathTooLongException lblStatus.Text = "There was an PathTooLongException when creating the directory" lblStatus.Text &= " in " & MapPath(".") & "\" & Constants.vbCr & "..." 'remove one character txtDir.Text = txtDir.Text.Substring(0, txtDir.Text.Length - 1) lblStatus.Text &= "Truncated Directory Name..." & Constants.vbCr GoTo start_try 'and try again Catch ex As Exception lblStatus.Text = ex.Message End Try lblStatus.Text &= "Directory successfully created!" & Constants.vbCr End Sub Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load End Sub End Class

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