cis 451: asp.net objects dr. ralph d. westfall january, 2009
Post on 31-Dec-2015
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Object Oriented Programming many popular newer programming
languages are object-oriented C++, Java, JavaScript
Visual Basic.NET is a true object-oriented (OO) language in contrast to VB 6 (which however
did have objects with very useful properties)
What Is an Object? 3 types of things grouped together
properties (like variables: descriptive) like a "super" variable (cf. hours PM)
methods (like functions: actions) events (things that it responds to)
similarities with real world objects car (properties? methods? events?) dog " "
Object Features properties: name/value pairs
age = 21; height = 66"; weight = 135#; methods: code that does something
calculations, write to screen, send e-mail may have either/both of following:
parameters (inputs) return values (outputs)
Object Features - 2 events: things happen, object responds
to them like a method, but triggered externally
user clicks a button, or time runs out can have parameters and/or return values
asynchronous: can occur at any time rather than scheduled, or at same time as
something else (synchronous)
Other Object Concepts class = template or general model instance of class has specific attributes telephone = class, my phone =
instance encapsulation: details of object hidden
inside a "black box" only need to know the interface: how to
call the methods and what the inputs and/or outputs are
Other Object Concepts - 2 "dot" notation identifies attributes
and methods of objects Request.TotalBytes Request.QueryString.Count
Count (of arguments) in QueryString is a property of Request Object
Response.Write() Write is a method of Response Object
ASP Core Objects Request: messages from caller (e.g.,
web page or process) Response: messages to caller
(browser) Server: variables and utility functions Application: data storage in memory
for all web pages in the application Session: identifies individual user
interactions
Request Object html or another asp file requests an asp
file Request Object has information from
page that requested the asp file information is stored in "collections"
contain pairs of variable names and their values (name/value pairs)
data values can be accessed by item name
Request.QueryString("page")
Request Object Data "get" method in HTML calling page
<form action="buya.aspx" method=get> "get" appends data to URL (URL encoding) limit around 1000 characters (256 –
2000+) data available in Request.QueryString
"collection," indexed by name of form element
Request.QueryString("page") form has textbox, textarea, checkbox, radio
button, or etc. element with name="page"
URL Encoding ? after URL shows start of data pairs of: name=value & (ampersands) between pairs + between separate words (= space) special characters coded as %nn (+ is
%2B) http://www.company.com/search.asp? …?cust=Jabbar&address=231+10th+St
example: try doing a Yahoo search
Request Object Data - 2 "post" method in HTML calling page
<form action="buya.aspx" method=post> sends data by a separate route size is essentially unlimited data available through Request.Form
"collection," indexed by name of form element
Request.Form("prod1") form has textbox, textarea, checkbox, radio
button, or etc. element with name="prod1"
Get versus Post get (Request.QueryString)
[object.property]) better for debugging (can look at query
string in URL box on browser) post (uses Request.Form)
can handle more data safer (less susceptible to hacking)
always use post for database updates
easy to convert Request.QueryString to Request.Form with global search/replace
Using QueryString in an aspx File
can create the same effect sending from an aspx file as from a html fileResponse.Redirect("rsp.aspx?Name=" & _
this.txtName.Text & "&LastName=" & _
this.txtLastName.Text) values are URL encoded and visible in
browser address of destination page one way to migrate from html to aspx
Response Object sends information to client
can control when and how to send it can control caching/expiration of
page can send parts or all of a web page
to client
Response Methods Response.Write(x1 [& " " & x2 [& ...]])
x1 etc. can be anything printable (text, #s, etc., or functions that return printable characters)
.NET has parentheses hold argument(s)
<%= x1 [& " " & x2 [& " " & etc.]%> same effect as Response.Write, in
less space less efficient (don't use <%= a lot)
Response Methods - 2 redirecting to another pageResponse.Redirect("buya.aspx") stops processing on current page and
goes to the other page can go to external pages too
Server Transfer Method can also use to redirect to another
page, but only if it's on same serverServer.Transfer("buya.aspx") doesn't change URL in browser
address comparison of Response.Redirect and
Server.Transfer
Exercise: Form Processing use Dreamweaver to create a form
that uses 8+ form elements/variations in its Windows>Objects>Forms toolbar
set name property for each element select options (e.g., text input can be
single or multiline, or password) see HTML Form Reference for syntax
save file as a .html file
Exercise: Form Processing - 2 use Visual Studio to
create a project add the .html file you created on the
previous page to the project create a .aspx file with Response.Write
statements to print inputs/selections from each input element from the .html file
test it on your workstation or computer
Multiple Selection Data can allow multiple selections in a
list box on a form <select size=2 name="loc" multiple> <option>Paris</option > <option>Sydney</option > <option>Buenos Aires</option > </select> may send multiple items with
same name ("loc" in this example)
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