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 Simple Calculator
Application-level error handling
<source lang="csharp">
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</source>
Catch exception and display exception message, Source and StackTrace (C#)
<source lang="csharp">
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">
<asp:Label ID="Label1" runat="server" Text="A:"></asp:Label>
<asp:TextBox ID="txtA" runat="server">5</asp:TextBox>
<asp:Label ID="Label2" runat="server" Text="B:"></asp:Label>
<asp:TextBox ID="txtB" runat="server">0</asp:TextBox>
<asp:Button ID="cmdCompute" runat="server" OnClick="cmdCompute_Click" Text="Divide A / B" />
<asp:Label ID="lblResult" runat="server" Font-Bold="True" ForeColor="Red"></asp:Label></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 = "Message: " + err.Message;
lblResult.Text += "
";
lblResult.Text += "Source: " + err.Source;
lblResult.Text += "
";
lblResult.Text += "Stack Trace: " + err.StackTrace;
lblResult.ForeColor = Color.Red;
}
}
}</source>
Divide By Zero With Exception
<source lang="csharp">
<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></source>
Generic error handler page
<source lang="csharp">
<%@ 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">
An unrecoverable error occurred and we"re still investigating the
reasons.
|
</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 = "No error information available.";
object o = Request.QueryString["ErrID"];
if (o != null)
errCode = (string) o;
ErrorCode.InnerHtml = errCode;
string referrer = "Error path not available.";
string temp = Request.UrlReferrer.ToString();
if (!String.IsNullOrEmpty(temp))
referrer = temp;
Referrer.InnerHtml = referrer;
}
}</source>
Page-level error handling
<source lang="csharp">
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</source>
Transfer to different page based on exception type
<source lang="csharp">
<%@ 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.
<form id="form1" runat="server">
- <asp:LinkButton ID="LinkButton1" runat="server" OnClick="LinkButton1_Click">Click to throw a NotImplementedException exception</asp:LinkButton>
- <asp:LinkButton ID="LinkButton2" runat="server" OnClick="LinkButton2_Click">Click to generate an internal error</asp:LinkButton>
- <asp:HyperLink ID="HyperLink1" runat="server" NavigateUrl="missing.aspx">Click to raise a HTTP 404 error</asp:HyperLink>
</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;
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());
}
}</source>
Try to catch error when converting text value to number
<source lang="csharp">
<%@ 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">
Simple Calculator
<asp:TextBox ID="txtValue" runat="server" />
<asp:Button Text="Do Math" runat="server" ID="btnDivide"
OnClick="btnDivide_Click" />
<asp:Label ID="labMessage" runat="server" />
</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";
}
}
}</source>
Use Global.asax to log application level exception
<source lang="csharp">
<%@ 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></source>
What is going to happen if there is no exception handler
<source lang="csharp">
<%@ 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">
</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;
}
}</source>
