Microsoft ASP Net 3.5 Step By Step (phần 15) pdf

Chapter 17 Diagnostics and Debugging 391 The code above traps the exception before the redirection happens. This gives you the oppor- tunity to log the exception (or, as in the example above, to show it in the System.Diagnostics .Debug context). You may also redirect users to a different page, if you want to hijack the exception handling before ASP.NET redirects to the page specifi ed in web.confi g. Be sure to call Context.ClearError fi rst to clear the error so ASP.NET won’t generate its standard error page. Summary Web development is diffi cult because an application’s state can be all over the place. For example, the application holds some of the state, the browser holds some of the state, and some of the state is stuck in a session database. In addition, the executing portions of an ap- plication happen in multiple places—both on the server and on the client. That calls for de- bugging techniques different from what you’d require with a desktop application. ASP.NET supports page-level tracing and application-level tracing. In both cases, ASP.NET displays the entire context of a request and response, including tracing statements. Visual Studio also supports debugging ASP.NET applications as though they were desktop ap- plications. You simply set up breakpoints, fi re up the debugger, and watch the fi reworks. 392 Part IV Diagnostics and Plumbing Debugging ASP.NET applications is very much like debugging desktop applications, thanks to Visual Studio. Moreover, the debugging works over a network, even the Internet. Finally, ASP.NET takes over the custom error page handling process (which used to be man- aged by IIS in classic ASP). You may direct users to new pages depending on the error that occurs. Finally, you can trap exceptions before they redirect and perform additional processing. Chapter 17 Quick Reference To Do This Prepare a Web site for debugging Include the following in web.confi g: <system.web> <compilation debug="true"/> </system.web> Enable tracing for an entire application Include the following in web.confi g: <system.web> <trace enabled="true"/> </system.web> Enable tracing for your page Set the Page class’s trace attribute to true by either using the property page in Visual Studio or declaring Trace=”true” in the page directive. Debug a Web application in Visual Studio Ensure that the debug attribute is turned on in web.confi g. Start the program running in debug mode by 1. Selecting Debug, Start Debugging from the main menu OR 2. Pressing the F5 key Set up breakpoints in an application in Visual Studio Place the cursor on the line at which you’d like to stop execution and 1. Select Debug, Toggle Breakpoint OR 2. Press the F9 key OR 3. Toggle the breakpoint by clicking the mouse in the gray ribbon to the left of the text in the code editor Execute a line of source code in the Visual Studio debugger While the debugger is running and execution has stopped at the line you’d like to execute 1. Select Debug, Step Over from the main menu OR 2. Press the F10 key To D o Th is Chapter 17 Diagnostics and Debugging 393 To Do This Step into a line of source code in the Visual Studio debugger While the debugger is running and execution has stopped at the line you’d like to execute 1. Select Debug, Step Into from the main menu OR 2. Press the F11 key Instruct ASP.NET to show a particular page when a specifi c HTTP error occurs Assign the error-handling page to the specifi c error in the <customErrors> section of web.confi g. Trap specifi c .NET exceptions or deal with general unhandled exceptions in ASP.NET Handle exceptions, including otherwise uncaught exceptions, within the Application_Error handler in Global.asax. Usually, you’d then redi- rect to a specifi c page. (Note that specifi c errors will be assigned as the InnerException of the HttpUnhandledException!) To Do Th is [...]... far, ASPX, ASAX, and ASCX files have seemed to magically work within ASP. NET For example, we saw earlier that simply surfing to an ASPX file causes ASP. NET to compile the file just in time and to synthesize a class based on System.Web.UI.Page The reason the ASPX files work that way is that ASP. NET includes handlers for that functionality ASP. NET HTTP handlers are specified in web.config in much the same way... Recognize the role of custom handlers in ASP. NET Write custom handlers Write just-in-time compiled custom handlers Configure your site to include your custom handler This chapter covers writing custom HTTP handlers In Chapter 2, we saw the ASP. NET pipeline Remember that the endpoint of all requests handled by ASP. NET is always an implementation of IHttpHandler ASP. NET includes several classes capable of... application starts up, the ASP. NET runtime looks in the web.config file to see if any additional handlers need to be attached to the pipeline (ASP. NET plugs in a number of modules already—they implement such features as authentication and session state.) When ASP. NET sees a new module within the web.config file, ASP. NET loads the module and calls the Init method Modules usually initialize by setting up handlers... the same role that ISAPI filters served for classic ASP as a place to insert functionality into the request processing HTTP Modules plug into the ASP. NET processing chain to handle applicationwide events in the same way that Global.asax handles applicationwide events In fact, many ASP. NET features are implemented through HTTP Modules Existing Modules ASP. NET employs HTTP Modules to enable features such... of custom handling is the Trace handler that is built into ASP. NET We looked at tracing in Chapter 17 You turn tracing on within the web.config file by inserting the trace element, This instructs the ASP. NET runtime to store summaries of the requests going through the site so they may be viewed for diagnostic purposes ASP. NET caches the tracing output in memory To view the trace... the third request Figure 19-3 shows the Internet Information Services (IIS) file mapping for files with the axd extension Although you won’t really see this aspect until deployment time, it’s interesting to observe because it shows how ASP. NET is very versatile in the kinds of requests it can handle IIS handles Trace.axd requests the same way as any other ASP. NET request That means IIS will pass requests... it can handle IIS handles Trace.axd requests the same way as any other ASP. NET request That means IIS will pass requests for resources with an extension of axd on to ASP. NET Once inside the ASP. NET pipeline, the web.config file tells ASP. NET to handle the request with the Trace handler 420 Part IV Diagnostics and Plumbing FIGURE 19-1 The output of the Trace.axd handler FIGURE 19-2 The output of the Trace.axd... web.config As with the HTTP modules, ASP. NET comes out of the box with several HTTP handlers already (for implementing features such as tracing and preventing access to sensitive files on the site) ASP. NET comes with these HTTP handlers already registered in the master web.config configuration file (which resides alongside machine.config in the main configuration directory) So far, ASPX, ASAX, and ASCX files have... Class1.) Change the name of the file to Timer.cs and the name of the class to Timer Place the code into the TimingModule namespace 3 The module as generated by Visual Studio doesn’t understand the ASP. NET types Add a reference to System.Web to make the ASP. NET types available 4 Add handlers for the beginning and ending of the request You may borrow the code from Global.asax if you want The signatures for... all requests The third element, type, is the name of the NET type assigned to handle the request Finally, the last attribute, validate, specifies whether or not ASP. NET should load the class at startup immediately or wait until a matching request is received Listing 19-1 includes a smattering of the HTTP handlers already installed as part of ASP. NET s master web.config file LISTING 19-1 Excerpt from the . type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version =3. 5. 0.0, Culture=neutral, PublicKeyToken =31 BF3 856 AD364E 35& quot; /></httpModules> </httpModules> </system.web> </configuration>. into the TimingModule namespace. 3. The module as generated by Visual Studio doesn’t understand the ASP. NET types. Add a reference to System.Web to make the ASP. NET types available. 4. Add handlers. Plumbing Debugging ASP. NET applications is very much like debugging desktop applications, thanks to Visual Studio. Moreover, the debugging works over a network, even the Internet. Finally, ASP. NET takes