Catch Multiple Exceptions using ASP.NET 2.0 and VB .NET

This tutorial will show you how to catch multiple exceptions using ASP.NET 2.0 and VB.NET

The .NET Framework offers a number of exception types that makes specifying multiple catch .. finally constructs easy.

In this example we will be catching exceptions when trying to create a directory in the filesystem, so we will need the System.IO namespace. We will also be specifying a finally block which ensures that some code will always execute after the try block executes. Our code will catch two exceptions if the user tries to create a directory that is 248 characters long or tries to specify an invalid character within the directory name (such as the asterisk character).

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 does two things: it lets exceptions thrown during the try block's execution to be caught by the catch block(s) below and ensures that execution can't leave the try block without running the finally block. In this example, we are specifying that our catch blocks handles exceptions of the type PathTooLongException and ArgumentException. We are also specifying a finally block which will execute immediately after our catch block(s).

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 Catch ex As ArgumentException lblStatus.Text = "There was a ArgumentException when creating the directory" lblStatus.Text &= " in " & MapPath(".") & "\" & Constants.vbCr Catch ex As Exception lblStatus.Text = ex.Message Finally If txtDir.Text.Length >= 248 Then lblStatus.Text &= "Directory length must be less than 248 chars!" & Constants.vbCr End If End Try

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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 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 Catch ex As ArgumentException lblStatus.Text = "There was a ArgumentException when creating the directory" lblStatus.Text &= " in " & MapPath(".") & "\" & Constants.vbCr Catch ex As Exception lblStatus.Text = ex.Message Finally If txtDir.Text.Length >= 248 Then lblStatus.Text &= "Directory length must be less than 248 chars!" & Constants.vbCr End If End Try 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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