Windows Systems Programming: Spring 2004
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ASP.NET
With ASP.NET we enter the world of distributed
processing using standard internet protocols
Accessing the class .NET server
About the Web.
-
HMTL revolutionized the way information is
delivered over the internet
-
Can use any text editor to create HTML pages
-
However support for dynamic content has been
a challenge
-
CGI (Common Gateway Interface) - mostly PERL - UNIX oriented servers
-
ASP - microsoft's server side programming
-
The Hypertext Transfer Protocol, better known
as HTTP, is the protocol that drives the World Wide Web. Invented by Tim
Berners-Lee ("father of the Web")
-
Here is a simple HTML page
<html>
<body>
Hello, world
</body>
</html>
If stored on a web server it can be accessed used its URL
(e.g. http://www.cs.odu.edu/~wild/cs477/spring04/simple.html)
- www.cs.odu.edu
resolves to an IP address (128.82.4.2) using a Domain Name Server (DNS)
- Browser opens a socket connection to that IP address uses
port "80" (usually)
- Transmit a HTTP request which might look like this
GET ~wild/cs477/spring04/simple.html HTTP/1.1
Accept: */*
Accept-Language: en-us
Accept-Encoding: gzip, deflate
If-Modified-Since: Wed, 24 Oct 2001 14:12:36 GMT
If-None-Match: "50b0d3ee955cc11:a78"
User-Agent: Mozilla/4.0.(compatible; MSIE.6.0; Windows NT 5.1)
Host: www.cs.odu.edu
Connection: Keep-Alive
[blank line]
- If all is well, then you should get the following HTTP
response
HTTP/1.1 200 OK
Server: Microsoft-IIS/5.0
Date: Wed, 24 Oct 2001 14:12:37 GMT
Content-Type: text/html
Accept-Ranges: bytes
Last-Modified: Wed, 24 Oct 2001 14:00:53 GMT
ETag: "d02acf81975cc11:a78"
Content-Length: 46
[blank line]
<html>
<body>
Hello, world
</body>
</html>
Dynamic HTML pages
<html>
<body>
<form>
<input type="text" name="op1" />
+
<input type="text" name="op2" />
<input type="submit" value=" = " />
</form>
</body>
</html>
-
When submitted, the two input "text" fields are
appended to the URL as parameters. e.g.
http://www.cs.odu.edu/~wild/cs477/spring03/Examples/Book1/Chap05/Calc/Calc.html?op1=3&op2=4
-
But how is the Sum computed? - the program to do this must be
stored at the server
- PERL
- ISAPI stands for Internet Server Application Programming
Interface
(Hosts DLL's which can contain COM objects, C++, other native code)
- ASP (Active Server Page) is very popular, for example
ISAPI Host for DLLs
-
One disadvantage to the above approaches is
that they are slow, first because they use scripting languages (which are
not compiled) and second because each server side program runs in it's own
process which is expensive to start up and stop.
-
ISAPI (Internet Server Application
Programming Interface) allows DLLs to be loaded into it's own process space
and run a compiled (e.g. C++) program
(ISAPI was the entry point for the code red virus however)
-
Here is an exmaple URL http://www.wintellect.com/calc.dll
-
Difficult to write - need to deal with HTTP
at a rather low level
Here is an example in C++ for the calculator
program
#include <windows.h>
#include <httpext.h>
#include <string.h>
#include <stdlib.h>
int GetParameter (LPSTR pszQueryString, LPSTR pszParameterName);
BOOL WINAPI DllMain (HINSTANCE hInstance, DWORD fdwReason,
LPVOID lpvReserved)
{
return (TRUE);
}
BOOL WINAPI GetExtensionVersion (HSE_VERSION_INFO* pVer)
{
pVer->dwExtensionVersion =
MAKELONG (HSE_VERSION_MINOR, HSE_VERSION_MAJOR);
lstrcpy (pVer->lpszExtensionDesc, "Calc ISAPI Extension");
return (TRUE);
}
DWORD WINAPI HttpExtensionProc (EXTENSION_CONTROL_BLOCK* pECB)
{
static char* szPrePostbackMessage =
"<html>\r\n" \
"<body>\r\n" \
"<form>\r\n" \
"<input type=\"text\" name=\"op1\" />\r\n" \
"+\r\n" \
"<input type=\"text\" name=\"op2\" />\r\n" \
"<input type=\"submit\" value=\" = \" />\r\n" \
"</form>\r\n" \
"</body>\r\n" \
"</html>";
static char* szPostPostbackMessage =
"<html>\r\n" \
"<body>\r\n" \
"<form>\r\n" \
"<input type=\"text\" name=\"op1\" value=\"%d\" />\r\n" \
"+\r\n" \
"<input type=\"text\" name=\"op2\" value=\"%d\" />\r\n" \
"<input type=\"submit\" value=\" = \" />\r\n" \
"%d\r\n" \
"</form>\r\n" \
"</body>\r\n" \
"</html>";
//
// Build the response message body.
//
char szMessage[512];
if (lstrlen (pECB->lpszQueryString) == 0) {
// If the query string is empty, return a page that shows
// an empty calculator.
lstrcpy (szMessage, szPrePostbackMessage);
}
else {
// If the query string is not empty, extract the user input,
// process it, and return a page that shows inputs and outputs.
int a = GetParameter (pECB->lpszQueryString, "op1");
int b = GetParameter (pECB->lpszQueryString, "op2");
wsprintf (szMessage, szPostPostbackMessage, a, b, a + b);
}
//
// Build the response message header.
//
char szHeader[128];
DWORD dwCount = lstrlen (szMessage);
wsprintf (szHeader, "Content-type: text/html\r\n" \
"Content-Length: %lu\r\n\r\n", dwCount);
//
// Output the response message header.
//
HSE_SEND_HEADER_EX_INFO shei;
shei.pszStatus = "200 OK";
shei.pszHeader = szHeader;
shei.cchStatus = lstrlen (shei.pszStatus);
shei.cchHeader = lstrlen (shei.pszHeader);
shei.fKeepConn = FALSE;
pECB->ServerSupportFunction (pECB->ConnID,
HSE_REQ_SEND_RESPONSE_HEADER_EX, &shei, NULL, NULL);
//
// Output the response message body.
//
pECB->WriteClient (pECB->ConnID, szMessage, &dwCount, 0);
//
// Indicate that the request was processed successfully.
//
return HSE_STATUS_SUCCESS;
}
int GetParameter (LPSTR pszQueryString, LPSTR pszParameterName)
{
char* p = strstr (pszQueryString, pszParameterName);
if (p != NULL) {
p += strlen (pszParameterName) + 1;
for (char* tmp = p; *tmp != '&' && *tmp != 0; tmp++)
; //// skip front part of URL
int len = tmp - p;
char* buffer = new char[len + 1];
strncpy (buffer, p, len);
int val = atoi (buffer);
delete buffer;
return val;
}
return 0;
}
ASP (Active Server Page)
<%@ Language="VBScript" %>
<html>
<body>
<form>
<input type="text" name="op1" value="<%= Request("op1") %>"/>
+
<input type="text" name="op2" value="<%= Request ("op2") %>" />
<input type="submit" value=" = " />
<%
If Request ("op1") <> "" And Request ("op2") <> "" Then
a = CInt (Request ("op1"))
b = CInt (Request ("op2"))
Response.Write (CStr (a + b))
End If
%>
</form>
</body>
</html>
-
F2: "<%" and "%>"
is an escape from HTML into the ASP scripting engine.
-
F3: Request returns the parameter value
passed in (if any) or the empty string if no form values submitted (like for
the first time displayed
-
F4: here is where the work gets done
ASP.NET
Similar in design philosophy with JSP (Java
Server Pages) - Compiles into program which is more efficient to execute and
which can run in an existing process for additional speed.
Uses .NET libraries
Example
<html>
<body>
<form runat="server">
<asp:TextBox ID="op1" RunAt="server" />
+
<asp:TextBox ID="op2" RunAt="server" />
<asp:Button Text=" = " OnClick="OnAdd" RunAt="server" />
<asp:Label ID="Sum" RunAt="server" />
</form>
</body>
</html>
<script language="C#" runat="server">
void OnAdd (Object sender, EventArgs e)// regular C# code
{
int a = Convert.ToInt32 (op1.Text);
int b = Convert.ToInt32 (op2.Text);
Sum.Text = (a + b).ToString ();
}
</script>
Here is the the HTML generated the first time displayed
(notice - there is no .NET stuff here)
<html>
<body>
<form name="_ctl0" method="post" action="calc.aspx" id="_ctl0">
<input type="hidden" name="__VIEWSTATE" value="dDwxOTE0NDY4ODE2Ozs+" />
<input name="op1" type="text" id="op1" />
+
<input name="op2" type="text" id="op2" />
<input type="submit" name="_ctl1" value=" = " />
<span id="Sum"></span>
</form>
</body>
</html>
Error Handling
This form expects numbers are input - if not
will cause an exception to be thrown - here is how to catch it
void OnAdd (Object sender, EventArgs e)
{
try {
int a = Convert.ToInt32 (op1.Text);
int b = Convert.ToInt32 (op2.Text);
Sum.Text = (a + b).ToString ();
}
catch (FormatException) {
Sum.Text = "Error";
}
}
Translates into .NET program which can be
compiled
Web Controls
Defined in "System.Web.UI.WebControls"
Some controls
include client side "scripts"
Web Controls
|
Class Name
|
Description
|
|
AdRotator
|
Displays rotating banners in Web forms
|
|
Button
|
Generates submit buttons
|
|
Calendar
|
Displays calendars with selectable dates
|
|
CheckBox
|
Displays a check box in a Web form
|
|
CheckBoxList
|
Displays a group of check boxes
|
|
CompareValidator
|
Validates user input by comparing it to another
value
|
|
CustomValidator
|
Validates user input using the algorithm of your
choice
|
|
DataGrid
|
Displays data in tabular format
|
|
DataList
|
Displays items in single-column or multicolumn lists
using HTML templates
|
|
DropDownList
|
Generates HTML drop-down lists
|
|
HyperLink
|
Generates hyperlinks
|
|
Image
|
Displays images in Web forms
|
|
ImageButton
|
Displays graphical push buttons
|
|
Label
|
Generates programmable text fields
|
|
LinkButton
|
Generates hyperlinks that post back to the server
|
|
ListBox
|
Generates HTML list boxes
|
|
Literal
|
Generates literal text in a Web form
|
|
Panel
|
Groups other controls
|
|
RadioButton
|
Displays a radio button in a Web form
|
|
RadioButtonList
|
Displays a group of check boxes
|
|
RangeValidator
|
Verifies that user input falls within a specified
range
|
|
RegularExpressionValidator
|
Validates user input using regular expressions
|
|
Repeater
|
Displays items using HTML templates
|
|
RequiredFieldValidator
|
Verifies that an input field isn’t empty
|
|
Table
|
Generates HTML tables
|
|
TextBox
|
Generates text input fields
|
|
ValidationSummary
|
Displays a summary of validation errors
|
|
Xml
|
Displays XML documents and optionally formats them
using XSLT
|
HTML Controls
-
The runat="server"
turns ordinary HTML into a HTML control which are defined in FCL’s
System.Web.UI.HtmlControls namespace.
-
See
documentation for events fired by each control.
-
Used to ease
burden of translating existing HTML forms
HTML Controls
|
Tag
|
Corresponding HTML Control
|
|
<a runat=“server”>
|
HtmlAnchor
|
|
<button runat=“server”>
|
HtmlButton
|
|
<form runat=“server”>
|
HtmlForm
|
|
<img runat=“server”>
|
HtmlImage
|
|
<input type=“button” runat=“server”>
|
HtmlInputButton
|
|
<input type=“reset” runat=“server”>
|
HtmlInputButton
|
|
<input type=“submit” runat=“server”>
|
HtmlInputButton
|
|
<input type=“checkbox” runat=“server”>
|
HtmlInputCheckBox
|
|
<input type=“file” runat=“server”>
|
HtmlInputFile
|
|
<input type=“hidden” runat=“server”>
|
HtmlInputHidden
|
|
<input type=“image” runat=“server”>
|
HtmlInputImage
|
|
<input type=“radio” runat=“server”>
|
HtmlInputRadioButton
|
|
<input type=“password” runat=“server”>
|
HtmlInputText
|
|
<input type=“text” runat=“server”>
|
HtmlInputText
|
|
<select runat=“server”>
|
HtmlSelect
|
|
<table runat=“server”>
|
HtmlTable
|
|
<td runat=“server”>
|
HtmlTableCell
|
|
<th runat=“server”>
|
HtmlTableCell
|
|
<tr runat=“server”>
|
HtmlTableRow
|
|
<textarea runat=“server”>
|
HtmlTextArea
|
|
Any other tag with runat=“server”
|
HtmlGenericControl
|
Page Level Events
How ASP.NET processes an .ASPX page
-
It creates a temporary file containing a
class derived from System.Web.UI.Page.
The Page class is one of the most
important classes in ASP.NET; it represents ASP.NET Web pages.
-
ASP.NET copies the code in the ASPX file,
as well as some code of its own, to the Page-derived
class. A method named OnAdd in a
<script> block in an ASPX file becomes a member method of the
derived class.
-
ASP.NET compiles the derived class and
places the resulting DLL in a system folder. The DLL is cached so that
steps 1 and 2 won’t have to be repeated unless the contents of the ASPX
file change.
-
ASP.NET instantiates the derived class
and “executes” it by calling a series of methods on it. It is during
this execution phase that the Page
object instantiates any controls declared inside it and solicits their
output.
Page Level Events can be used to execute event
handlers. For example. Suppose you wanted today's date and the next four dates
in a drop down list - you can statically initialize like this
<asp:DropDownList ID="MyList" RunAt="server">
<asp:ListItem Text="February 21, 2003" RunAt="server" />
<asp:ListItem Text="February 22, 2003" RunAt="server" />
<asp:ListItem Text="February 23, 2003" RunAt="server" />
<asp:ListItem Text="February 24, 2003" RunAt="server" />
<asp:ListItem Text="February 25, 2003" RunAt="server" />
</asp:DropDownList>
But this is only good for one day - to generate list as needed
<asp:DropDownList ID="MyList" RunAt="server" />
.
.
.
<script language="C#" runat="server">
void Page_Load (Object sender, EventArgs e)
{
if (!IsPostBack) {
for (int i=0; i<5; i++) {
DateTime date =
DateTime.Today + new TimeSpan (i, 0, 0, 0);
MyList.Items.Add (date.ToString ("MMMM dd, yyyy"));
}
}
}
</script>
Page-Level Directives
ASP.NET @ Directives
|
Directive
|
Description
|
|
@ Page
|
Defines general attributes and compilation settings
for ASPX files
|
|
@ Control
|
Defines general attributes and compilation settings
for ASCX files
|
|
@ Import
|
Imports a namespace
|
|
@ Assembly
|
Enables linkage to assemblies not linked to by
default
|
|
@ Register
|
Registers user controls and custom controls for use
in a Web form
|
|
@ OutputCache
|
Exerts declarative control over page caching and
fragment caching
|
|
@ Reference
|
Adds a reference to an external ASPX or ASCX file
|
|
@ Implements
|
Identifies an interface implemented by a Web page
|
Currency Converter: An Example
<%@ Import Namespace=System.Data %>
<html>
<body>
<h1>Currency Converter</h1>
<hr>
<form runat="server">
Target Currency<br>
<asp:ListBox ID="Currencies" Width="256" RunAt="server" /><br>
<br>
Amount in U.S. Dollars<br>
<asp:TextBox ID="USD" Width="256" RunAt="server" /><br>
<br>
<asp:Button Text="Convert" ID="ConvertButton" Width="256"
RunAt="server" /><br>
<br>
<asp:Label ID="Output" RunAt="server" />
</form>
</body>
</html>
<script language="C#" runat="server">
void Page_Init (Object sender, EventArgs e)
{
// Wire the Convert button to OnConvert
ConvertButton.Click += new EventHandler (OnConvert);
}
void Page_Load (Object sender, EventArgs e)
{
// If this isn't a postback, initialize the ListBox
if (!IsPostBack) {
DataSet ds = new DataSet ();
ds.ReadXml (Server.MapPath ("Rates.xml"));
foreach (DataRow row in ds.Tables[0].Rows)
Currencies.Items.Add (row["Currency"].ToString ());
Currencies.SelectedIndex = 0;
}
}
void OnConvert (Object sender, EventArgs e)
{
// Perform the conversion and display the results
try {
decimal dollars = Convert.ToDecimal (USD.Text);
DataSet ds = new DataSet ();
ds.ReadXml (Server.MapPath ("Rates.xml"));
DataRow[] rows = ds.Tables[0].Select ("Currency = '" +
Currencies.SelectedItem.Text + "'");
decimal rate = Convert.ToDecimal (rows[0]["Exchange"]);
decimal amount = dollars * rate;
Output.Text = amount.ToString ("f2");
}
catch (FormatException) {
Output.Text = "Error";
}
}
</script>
-
F8: Serves same function as
"Using" in C# program
-
F9: uses XML file as a data source
-
F10: Treats XML file like a 1 table
database
-
F11: Uses SQL "Select" statement
Look at the XML file
<?xml version="1.0"?>
<Rates>
<Rate>
<Currency>British Pound</Currency>
<Exchange>0.698544</Exchange>
</Rate>
<Rate>
<Currency>Canadian Dollar</Currency>
<Exchange>1.57315</Exchange>
</Rate>
<Rate>
<Currency>French Franc</Currency>
<Exchange>7.32593</Exchange>
</Rate>
<Rate>
<Currency>German Mark</Currency>
<Exchange>2.18433</Exchange>
</Rate>
<Rate>
<Currency>Italian Lira</Currency>
<Exchange>2162.67</Exchange>
</Rate>
<Rate>
<Currency>Japanese Yen</Currency>
<Exchange>122.742</Exchange>
</Rate>
<Rate>
<Currency>Mexican Peso</Currency>
<Exchange>9.22841</Exchange>
</Rate>
<Rate>
<Currency>Swiss Franc</Currency>
<Exchange>1.64716</Exchange>
</Rate>
</Rates>
Copyright chris wild 1999-2004.
For problems or questions regarding this web contact [Dr.
Wild].
Last updated: February 05, 2004.