ASP.NET Tutorial/Development/Exception

Содержание

1 Application-level error handling
2 Catch exception and display exception message, Source and StackTrace (C#)
3 Divide By Zero With Exception
4 Generic error handler page
5 Page-level error handling
6 Transfer to different page based on exception type
7 Try to catch error when converting text value to number
8 Use Global.asax to log application level exception
9 What is going to happen if there is no exception handler

Application-level error handling

Protected Sub Application_Error(sender as Object, ByVal e As System.EventArgs)
    Dim bigError As System.Exception = Server.GetLastError()
    If (TypeOf AnError.GetBaseException() Is HttpRequestValidationException) Then
        System.Diagnostics.Trace.WriteLine(bigError.ToString)
        Server.ClearError()
    End If
End Sub

Catch exception and display exception message, Source and StackTrace (C#)

File: Default.aspx
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="ErrorHandlingTest" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
    <title>Untitled Page</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:Label ID="Label1" runat="server" Text="A:"></asp:Label>
        <asp:TextBox ID="txtA" runat="server">5</asp:TextBox><br />
        <asp:Label ID="Label2" runat="server" Text="B:"></asp:Label>
        <asp:TextBox ID="txtB" runat="server">0</asp:TextBox><br />
        <br />
        <asp:Button ID="cmdCompute" runat="server" OnClick="cmdCompute_Click" Text="Divide A / B" /><br />
        <br />
        <br />
        <asp:Label ID="lblResult" runat="server" Font-Bold="True" ForeColor="Red"></asp:Label></div>
    </form>
</body>
</html>
File: Default.aspx.cs
using System;
using System.Data;
using System.Configuration;
using System.Collections;
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.Drawing;
public partial class ErrorHandlingTest : System.Web.UI.Page
{
    protected void cmdCompute_Click(object sender, EventArgs e)
    {
        try
        {
            decimal a, b, result;
            a = Decimal.Parse(txtA.Text);
            b = Decimal.Parse(txtB.Text);
            result = a / b;
            lblResult.Text = result.ToString();
            lblResult.ForeColor = Color.Black;
        }
        catch (Exception err)
        {
            lblResult.Text = "<b>Message:</b> " + err.Message;
            lblResult.Text += "<br /><br />";
            lblResult.Text += "<b>Source:</b> " + err.Source;
            lblResult.Text += "<br /><br />";
            lblResult.Text += "<b>Stack Trace:</b> " + err.StackTrace;
            lblResult.ForeColor = Color.Red;
        }
    }
}

Divide By Zero With Exception

<script language="C#" runat="server">
protected void Page_Load(object o, EventArgs e) {
    try {
        int x;
        int y;
        x = 5;
        y = 0;
        int result = x / y;
        string message = "result is: " + result;
        Response.Write(message);
    }
    catch(DivideByZeroException) {
        Response.Write("divisor can"t be zero");
    }
}
</script>

Generic error handler page

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" 
    Inherits="Samples_GenericError" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
    <title>Unrecoverable Error</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
       <table>
        <tr>
            <td>
                An <strong>unrecoverable</strong> error occurred and we"re still investigating the
                reasons.<br />
                <b>Error code:&nbsp;</b><span runat="server" id="ErrorCode"></span><br />
                <b>Error path:&nbsp;</b><span runat="server" id="Referrer"></span>
            </td>
        </tr>
        </table>
    </div>
    </form>
</body>
</html>
File: Default.aspx.cs
using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;
public partial class Samples_GenericError : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        string errCode = "<i>No error information available.</i>";
        object o = Request.QueryString["ErrID"];
        if (o != null)
             errCode = (string) o;
         ErrorCode.InnerHtml = errCode;
        string referrer = "<i>Error path not available.</i>"; 
        string temp = Request.UrlReferrer.ToString();
        if (!String.IsNullOrEmpty(temp))
            referrer = temp;
        Referrer.InnerHtml = referrer;
    }
}

Page-level error handling

Protected Overrides Sub OnError(ByVal e As System.EventArgs)
    Dim AnError As System.Exception = Server.GetLastError()
    If (TypeOf AnError.GetBaseException() Is SomeSpecificException) Then
        Response.Write("Something bad happened!")
        Response.StatusCode = 200
        Server.ClearError()
        Response.End()
    End If
End Sub

Transfer to different page based on exception type

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" 
    Inherits="Default"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
    <title>Exceptions at work</title>
</head>
<body>
    To test this page effectively, first disable the customErrors section in the web.config file and 
                then try again with the section enabled.
    <div id="pageContent">
        <form id="form1" runat="server">
            <ul><li>
            <asp:LinkButton ID="LinkButton1" runat="server" OnClick="LinkButton1_Click">Click to throw a NotImplementedException exception</asp:LinkButton> 
            </li><li>
            <asp:LinkButton ID="LinkButton2" runat="server" OnClick="LinkButton2_Click">Click to generate an internal error</asp:LinkButton></li>
                <li>
            <asp:HyperLink ID="HyperLink1" runat="server" NavigateUrl="missing.aspx">Click to raise a HTTP 404 error</asp:HyperLink></li>
            </ul>
        </form>
    </div>
</body>
</html>
File: Default.aspx.cs
using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class Default : System.Web.UI.Page
{
    protected void Page_Error(object sender, EventArgs e)
    {
        Exception ex = Server.GetLastError();
        if (ex is NotImplementedException)
            Server.Transfer("/notimplementedexception.aspx");
        else
            Server.Transfer("/apperror.aspx");
        Server.ClearError();
    }
    protected void Page_Load(object sender, EventArgs e)
    {
    }
  protected void LinkButton1_Click(object sender, EventArgs e)
  {
    throw new NotImplementedException("The feature you requested is not implemented yet.");
  }
  protected void LinkButton2_Click(object sender, EventArgs e)
  {
        string test = null;
        Response.Write(test.ToString());
  }
}

Try to catch error when converting text value to number

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="TryCatch" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
    <title>Try...Catch Example</title>
</head>
<body>
   <form id="form1" runat="server">
   <div id="container">
   <h1>Simple Calculator</h1>
   <div class="box">
      <asp:TextBox ID="txtValue" runat="server" />
      <br />
      <asp:Button Text="Do Math" runat="server" ID="btnDivide" 
         OnClick="btnDivide_Click" />
   </div>
   <asp:Label ID="labMessage" runat="server" />
   </div>
   </form>
</body>
</html>
File: Default.aspx.cs
using System;
using System.Data;
using System.Configuration;
using System.Collections;
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;
public partial class TryCatch : System.Web.UI.Page
{
   protected void btnDivide_Click(object sender, EventArgs e)
   {
        try
        {
           double dVal = Convert.ToDouble(txtValue.Text);
           double result = dVal * 100.0;
        
           labMessage.Text = txtValue.Text + "* 100.0";
           labMessage.Text += "=" + result;
        }
        catch (FormatException ex1)
        {
           labMessage.Text = "Please enter a valid number";
        }
        catch (Exception ex2)
        {
           labMessage.Text = "Unable to compute a value with these values";
        }
   }
}

Use Global.asax to log application level exception

<%@ Application Language="C#" %>
<%@ Import Namespace="System.Diagnostics" %> 
<%@ Import Namespace="System.Text" %>
<script runat="server">
    void Application_Start(object sender, EventArgs e) 
    {
        // Code that runs on application startup
    }
    
    void Application_End(object sender, EventArgs e) 
    {
        //  Code that runs on application shutdown
    }
        
    void Application_Error(object sender, EventArgs e) 
    {
        // Obtain the URL of the request 
        string url = Request.Path;
        // Obtain the Exception object describing the error 
        Exception error = Server.GetLastError();
        // Build the message --> [Error occurred. XXX at url]
        StringBuilder text = new StringBuilder("Error occurred. ");
        text.Append(error.Message);
        text.Append(" at ");
        text.Append(url); 
        // Write to the Event Log 
        EventLog log = new EventLog();
        log.Source = "Core35 Log";
       // log.WriteEntry(text.ToString(), EventLogEntryType.Error);
    }
</script>

What is going to happen if there is no exception handler

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="DivideByZero_aspx" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
    <title>Untitled Page</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
    
    </div>
    </form>
</body>
</html>
File: Default.aspx.cs
using System;
using System.Data;
using System.Configuration;
using System.Collections;
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;
public partial class DivideByZero_aspx : System.Web.UI.Page
{  
    protected void Page_Load(object sender, EventArgs e)
    {
        int i = 0;
        int j = 1;
        int k = j/i;
    }
}

ASP.NET Tutorial/Development/Exception

Содержание

Application-level error handling

Catch exception and display exception message, Source and StackTrace (C#)

Divide By Zero With Exception

Generic error handler page

Page-level error handling

Transfer to different page based on exception type

Try to catch error when converting text value to number

Use Global.asax to log application level exception

What is going to happen if there is no exception handler

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