CIS 451: ASP.NET Debugging and Server-Side Includes

CIS 451: ASP.NET Debugging and Server-Side Includes Dr. Ralph D. Westfall February, 2009

Error Handling/Debugging • client side vs. server scripts • syntax errors • logical errors • good coding practices to minimize errors • testing your code • debugging statements

Need to Identify as Server Script • code will run on client if doesn't have: • <% • [code] • %> • or • <script language="VB" runat="server"> • [code] • </script> • filetype needs to be .aspx, not .htm(l)

Syntax Errors • spelling • Reesponse.Write("something") • EndIf '2 words: needs a space • missing parts of control structures • For but no Next • If but no End If • extra parts for control structures • extra Next or extra End If at end

Syntax Errors - 2 • using a method as a property • Response.Write = "Welcome" • don't use = with methods • using a property as a method • buffer("true") • properties are values, so need to use =

Syntax Errors - 3 • writing to a "read only" property Dim prices() As Double = {3.00, 2.00} prices.Length = 5 'read only property • using Set to create an object • Set objMail = _ Server.CreateObject("CDO.Message") • 'remove Set (ASP 3.0 still needs Set)

Logical Errors • division by a variable that has value of zero if Option Explicit or Strict is not On • a = 2 • c = a / b 'no value given for b • type mismatch • e.g. can't do arithmetic with text • 5 / "hello" • missing period can cause a type mismatch • a=CInt(RequestQueryString("card")) • 5 / a

Good Coding Practices • indent code inside loops and conditionals • "pretty listing" (automatic in VS.NET) • For intI = 0 to 2 • intJ = intI • Next I • use comments where appropriate • 'single quote creates a comment

Good Coding Practices - 2 • use Option Strict at start of file <%@ Page Language="vb" Strict="true"%> • forces you to use Dim for all variables • helps spot spelling mistakes • forces you to handle all type conversions explicitly txtCount.Text=CStr(intCount)

Good Coding Practices - 3 • use consistent object naming prefixes • btnSubmit 'a button • txtLastName 'a textbox for data • capitalize function names e.g. conversions • CInt(7.3) 'Convert to Integer • CCur(9.9) 'Convert to Currency

Good Coding Practices - 4 • type checking: is data what you expect? • If IsNumeric(Request.Form("num")) Then • intTot = intTot + intNum • End If • type conversion: change data so it is usable • intValue = CInt(dblItem1 + dblItem2)

Good Coding Practices - 5 • use subprocedures and/or functions • for anything substantial (5 or more lines?) that gets done in more than 1 place • advantages: • shorter program • easier to debug and maintain • may be able to reuse them in other programs

Good Coding Practices - 6 • use "server-side includes" in .aspx files • <% 'prices.aspx file • Dim dblProdPrice(11) • dblProdPrice(0)=29.99 'etc. • %> • <html>  •  • advantages similar to subprocedures, etc. See Notes Page

Testing Your Code • test the different ways a user could go through the application • example: shopping cart with 2 catalog pages • entry page to catalog page 1 to checkout • entry page to catalog page 2 to checkout • entry, catalog 1, catalog 2, checkout • entry, catalog 2, catalog 1, checkout • using browser Back button instead of form button? • using link instead of button?

Testing Your Code - 2 • test possible data values • example: zip codes • boundary values (included, or not?) • 00000 and 99999 • values in between boundaries • 00001 to 99998 • out-of-bounds values • negative #s? 6 digit #s? • text #s? (ninety thousand and one)

VS Debugging Capabilities • break points and icons for stepping through code • Step Into, Step Over, Step Out • special windows • Locals, Output, Watch, View Stack, etc.

Debugging Statements • insert "trace" statements to determine values before code where problem is • Response.Write([variable name]) • use <form method="get" > so you can see form input values in query string • MsgBox to show specific values

Debugging with "Include" Files • some programmers put tracing procedures in separate file • add #include file=[trace file name] at top of file being debugged • need to then insert calls to trace file procedures in code • NET tracing capabilities

More on Server Side Includes • special features for HTML files only? • extension is .shtml or .shtm so server knows that special processing required • #fsize - gives file size • #flastmod - gives file last modified date • include works in both ASP and HTML • # include - includes text (code) from another file so it is processed as if it is in the current file

Server Side Include Issues • data is text, so could use .txt as extension • can hide file by using .aspx extension • Microsoft recommends .inc extension • to conveniently identify include files • convenient way to keep data in programs up-to-date • e.g., put shopping cart product prices data in an include, then update just that file

Using Server Side Includes in ASP.NET • need to put "directive" in HTML comments <!--#include file="file1.aspx"-> 'path not needed if in current directory • can use physical path (address on drive) <!--#include file="[C:\path\]file.aspx"-> • can also use virtual path (server address) <!--#include virtual="[path]/file.aspx"->

SSI Exercise • view Using Server Side Includes • click "basic page," View>Source, edit URLs and Save As basic.shtml • note: save it as .shtml, not .html • also save code for the other linked pages (includes) in same directory • modify include files • view effects on basic.shtml in browser

CIS 451: ASP.NET Debugging and Server-Side Includes