Throwing an Exception using ASP.NET 2.0 and C# .NET

This tutorial will show you how to throw exceptions using ASP.NET 2.0 and C#.NET

Throwing exceptions are easy to do in C# .NET.

In this example we will be throwing exceptions when trying to create a directory in the filesystem, so we will need the System.IO namespace. 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).

using 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 a finally block. In this example, we are specifying that our catch blocks handles exceptions of the type PathTooLongException and ArgumentException. We are also adding an if block that will throw an ArgumentException if there is a "\" character in the directory name.

try { Directory.CreateDirectory(MapPath(".") + "\\" + txtDir.Text); // adding this line throws an ArgumentException even if the \ character is normally valid if (txtDir.Text.Contains("\\")) { throw new ArgumentException("Directory name cannot contain the \"\\\" character"); } } catch (PathTooLongException ex) { lblStatus.Text = "There was an PathTooLongException when creating the directory"; lblStatus.Text += " in " + MapPath(".") + "\\" + "\r"; } catch (ArgumentException ex) { lblStatus.Text = "There was a ArgumentException when creating the directory"; lblStatus.Text += " in " + MapPath(".") + "\\" + "\r"; lblStatus.Text += ex.Message + "\r"; } catch (Exception ex) { lblStatus.Text = ex.Message; }

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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.

using System; using System.Data; using System.Configuration; using System.Web; using System.Web.Security; using System.Web.UI; using System.Web.UI.WebControls; using System.Web.UI.WebControls.WebParts; using System.Web.UI.HtmlControls; using System.IO; public partial class _Default : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) { } protected void btnSubmit_Click(object sender, EventArgs e) { try { Directory.CreateDirectory(MapPath(".") + "\\" + txtDir.Text); // adding this line throws an ArgumentException even if the \ character is normally valid if (txtDir.Text.Contains("\\")) { throw new ArgumentException("Directory name cannot contain the \"\\\" character"); } } catch (PathTooLongException ex) { lblStatus.Text = "There was an PathTooLongException when creating the directory"; lblStatus.Text += " in " + MapPath(".") + "\\" + "\r"; } catch (ArgumentException ex) { lblStatus.Text = "There was a ArgumentException when creating the directory"; lblStatus.Text += " in " + MapPath(".") + "\\" + "\r"; lblStatus.Text += ex.Message + "\r"; } catch (Exception ex) { lblStatus.Text = ex.Message; } } }

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