ASP.NET and Web Services

The following comments and examples apply to ASP.NET 2.0. The examples were created used ASP.NET Express Edition (see http://www.asp.net/).

A simple ASP.NET application has:

A web file with extension .aspx that contains the Web pages GUI
An optional code-behind file containing code to support the display/function of the web page. The file is names the same as the web page with a .apsx.vb (assuming VB is used)

The code in the code-behind file can actually be incorporated in the web file. The purpose of the code-behind file is to promote code reuse.

The ubiquitous “Hello World”

A very simple ASP page that initially displays a page with one ASP button and label and when clicked redisplays the page with “Hello World” is below. Note that ASP controls are handled differently that ‘regular’ HTML buttons

Web File named HelloWorld.aspx

<%@ Page Language="VB" AutoEventWireup="false" CodeFile="HelloWorld.aspx.vb" Inherits="_Default" %>

<-- above denotes page to be processes as ASP page, VB is used, codebehind file name given, and class ‘HelloWorld’ to inherit from -->

<-- AutoEventWireup=”false” tells VB to generate the Page_Load and Page_Init events without Handles keywords. Always set to false -->

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<title>Hello World</title>

</head>

<body>

<div>

<-- asp:Button indicates ASP control that is to run at server -->

<asp:Button ID="Button1" runat="server" Text="Click Me" Width="124px" /><br />

<br />

<asp:Label ID="Label1" runat="server" Width="212px"></asp:Label> <br />

<br />

</div>

</form>

</body>

</html>

Code-behind file named HelloWorld.aspx.vb

Partial Class _Default

Inherits System.Web.UI.Page

Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click

' When button1 clicked on page the server processes the click and assigns “Hello World” to asp Label1

Label1.Text = "Hello World"

End Sub

End Class

Validation Controls

A validation control determines if the data entered in another control is in the proper format. A validator is converted to JavaScript (as referred to as ECMAScript – European Computer Manufacturer’s Association) and is executed on the client.

If the client does not support scripting or scripting is disabled the validation is performed on the server.

The following shows a simple page with entry for a phone number, including area code. Validation controls will check to see 1) a phone number value is entered, and 2) the phone number is entered with the format nnn-nnn-nnnn. The validators are executed on the client prior to the postback to the server when the ‘Submit’ button is pressed. If either validator fails an error message is diplayed.

Assuming a phone number is entered and of the correct format, the server postback logic is executed. The page is redisplayed with a validation message based on the value of the phone number.

Validator.aspx file

<%@ Page Language="VB" AutoEventWireup="false" CodeFile="Validator.aspx.vb" Inherits="_Default" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<title>Untitled Page</title>

</head>

<asp:Label ID="lblPhoneNumber" runat="server" Text="Please enter your phone number, area code first below:"

Width="353px"></asp:Label><br />

<br />

<asp:TextBox ID="tbPhoneNumber" runat="server"></asp:TextBox> 

<asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ControlToValidate="tbPhoneNumber"

ErrorMessage="Invalid number. Please reenter."></asp:RequiredFieldValidator>

<br />

(format nnn-nnn-nnnn)      

<asp:RegularExpressionValidator ID="RegularExpressionValidator1" runat="server" ErrorMessage="Invalid number. Please reenter." ValidationExpression='\d{3}-\d{3}-\d{4}' ControlToValidate="tbPhoneNumber"></asp:RegularExpressionValidator><br />

<br />

<asp:Button ID="btnSubmit" runat="server" Text="Submit" Width="83px" /><br />

<br />

 <asp:Label ID="lblVerifiedNumber" runat="server" Visible="False" Width="284px"></asp:Label></div>

</form>

</body>

</html>

Validator.aspx.vb file

Partial Class _Default

Inherits System.Web.UI.Page

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

If IsPostBack Then

If (tbPhoneNumber.Text = "123-456-7890") Then

lblVerifiedNumber.Text = "Number is validated"

Else

lblVerifiedNumber.Text = "Number not validated. Try 123-456-7890."

End If

lblVerifiedNumber.Visible = True

End If

End Sub

End Class

Maintaining Session Information and State

Values can be held across pages using several mechanisms

Save values in ‘hidden’ fields	A general method for saving values. Not ASP specific
Set EnableViewState=true	A APS.NET feature to retain a Web controls value when a postback occurs. The web control value is contained in a hidden field named _VIEWSTATE and stores the all Web control data values as an encoded string The ASP.NET IDE handles the storing of values automatically
Save values in Cookies	A non-ASP specific feature that save keyword/value pairs on the client between callbacks to the server. The cookie logic is implemented in the server ASP.NET code Creating a cookie … Dim cookie As HttpCookie … cookie = new HttpCookie(keyword, value) Response.Cookies.Add(cookie) … Retrieving values from cookies Dim cookies As HttpCookieCollection Dim keyword as String Dim value as String … cookies = Request.Cookies If (((cookies Is Nothing) = False) AndAlso cookies.Count > 0) Then For i = 0 to cookies.Count - 1 keyword = cookies(i).Name value = cookies(i).Value Next …. Note: If session tracking is enabled (ie EnableSessionState="True" property is set in the .aspx page ) then the first cookie (index 0) is the session id cookie – APS.NET_SessionId) ???? Cookie properties: Name – Returns a string with cookies name. Value – Returns a string with the cookies value Domain – Returns a string giving domain of web server from which cookie was loaded Expires – Returns a DateTime object of when the cookie expires Path - Returns a string with URL prefix for the cookie Secure – Returns Boolean indicating if cookie should be transmitted via a secure protocol
HttpSessionState	Enables session tracking via the HttpSessionState class. An HttpSessionState object stores values in keyword/value pairs like cookies, but the values can be objects other than strings. Adding values to HttpSessionState object Values are added via the Session object … Session.Add(keyword, value) … Obtaining values from the Session object. sessionid = Session.SessionID timeout = Session.Timeout If Session.count <> 0 Then For i = 0 to Session.Count – 1 keyname = Session.Keys(i) Value = Session(keyname) Next End If Session properties Count – number of keyword/value pairs in Session object IsNewSession – Boolean to indicate whether the session was created during the loading of the current page IsReadOnly – Boolean to indicate if Session object is read only SessionId – Returns session’s unique ID Timeout – Specifies the maximum number of minutes a session can be inactive before the session expires. Default is 20 minutes.

Adding Web User Controls

A web user control could be something as simple as an image or more complex like a menu bar. Changes to the user control are therefore isolated. Only the web user control file needs to be maintained as opposed to all web pages that use the control.

Web user controls are defined to the web page via <%@ Register webcontrol %> directive.

Web user controls consist of 2 pages – the ASCX and the code behind file (assuming you use a code-behind file).

The web page the uses/displays the web control

<%@ Register TagPrefix=”Header” Tagname=”MyWebControl” Scr=”MyWebControl.ascx” %>

….

<Header:MyWebControl id=”MyWebControl1” runat=”server” >

</Header>

MyWebControl.ascx file - assumes an image

<@ Control Language = “vb” AutEventWireup=”false” Codebehind=”MyWebControl.ascx.vb” Inherits=”Project.MyWebControl” TargetSchema=”http://dodads.com/images” %>

<asp:Control id=”mycontrol” runat=”sever” ImageUrl=http://www.dodads.com/images/controlimage.png

<asp:Control/>

MyWebControl.ascx.vb – include any code like any other code behind file

Web Services

A web service is a class running on one machine that responds to requests for information originating from another machine.

Common data formats and protocols such as XML and HTTP are used for data communication.

In .NET the method calls are implemented using SOAP – Simple Object Access Protocol. SOAP is an XML formatted message than can be transferred via HTTP.

The .Net class developed is placed in the application \bin directory.

More than one method can be implemented in a Web Service. The methods are executed via RPC – Remote Procedure Calls. The methods are marked with a WebMethod attribute, and via this attribute the method is exposed for use via other classes through an RPC.

A web service is composed of 1 or 2 parts: a ASMX file and, if you want the executable code in a separate file, the code-behind file. The ASMX file can be viewed in any browser can contains information on the use of the web service methods and optionally the method logic. Optionally the code-behind file provides the implementation of the methods

The display of the ASMX file on a browser contains:

A link to the Service Description, an XML document (conforms to WSDL – Web Service Decription Language) that details how a web service behaves. The WSDL document defines the methods that the web service makes available and the ways the calling client can execute those methods and receive the reply.

A list of methods that are provided by the service. Clicking on any method displays a test page where parameters can be entered and the service method can be executed on clicking the ‘Invoke’ button.

Sample request and response messages using SOAP, HTTP GET and HTTP POST protocols (the protocols are also sometimes referred to as the wire protocol or wire format

SOAP is the default protocol for web services in .NET. SOAP supports a wider variety of data types such as DataSet, DateTime, XmlNode, arrays, and user-defined data types – compared to the other protocols.

An application that uses a web service consists of a proxy class (representing the web service) and the client application that interacts with the web service.

The proxy class handles the call(s) to the web service and passing of method values and receiving the results of the web service.

Examples of a web service are below. It is a simple service that concatenates 2 strings together

Concatenate.asmx with method logic included (no code behind file)

<%@ WebService Language="VB" Class="Concatenate" %>

Imports System.Web

Imports System.Web.Services

Imports System.Web.Services.Protocols

<WebService(Namespace := "http://tempuri.org/")> _

<WebServiceBinding(ConformsTo:=WsiProfiles.BasicProfile1_1)> _

Public Class Concatenate

Inherits System.Web.Services.WebService

<WebMethod(Description:="Concatenate 2 strings together")> _

Public Function Concat(ByVal firstString As String, ByVal secondString As String) As String

Return firstString & secondString

End Function

End Class

VB.NET program that uses the Concatenate web service. Note a Web reference to Concatenate.asmx was added to the project. The form had 2 input fields for the strings to concatenate, a result field, and a submit button.

Imports System.ComponentModel

Imports System.Web.Services.Protocols

Public Class Form1

Private remoteConcatenate As localhost.Concatenate

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

remoteConcatenate = New localhost.Concatenate

End Sub

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnExecute.Click

tbResults.Text = remoteConcatenate.Concat(tbString1.Text, tbString2.Text)

End Sub

Private Sub tbString1_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles tbString1.TextChanged

End Sub

End Class

Session Tracking in Web Services

Session tracking can be used by clients of Web services in the same manner as a client of an ASP.Net web user.

The client must have enabled cookies so that a session id can be received from and returned to the web service.

The web service will utilize session info based on each method defined to use session tracking.

Service.vb – A web service that returns the time along with a session id, concatenated with prior requests.

Imports System.Web

Imports System.Web.Services

Imports System.Web.Services.Protocols

<WebService(Namespace:="http://tempuri.org/")> _

<WebServiceBinding(ConformsTo:=WsiProfiles.BasicProfile1_1)> _

<Global.Microsoft.VisualBasic.CompilerServices.DesignerGenerated()> _

Public Class Service

Inherits System.Web.Services.WebService

<WebMethod(EnableSession:=True, Description:="Return current (server) time plus all prior times you asked for time")> _

Public Function GetTheTime() As String

Dim allTimes As String

allTimes = CType(Session("time"), String)

If allTimes Is Nothing Then

allTimes = GetCurrentTime() & "|" & Session.SessionID

Else

allTimes = GetCurrentTime() & "|" & Session.SessionID & "|" & allTimes

End If

Session.Add("time", allTimes)

Return allTimes

End Function

Public Function GetCurrentTime() As String

Return String.Format("{0:D2}:{1:D2}:{2:D2}", _

DateTime.Now.Hour, DateTime.Now.Minute, _

DateTime.Now.Second)

End Function

End Class

DisplayTimeFromService.vd – A VB.NET app that calls the service. Remember to define the service via Project/Add Web Reference

Imports System.Net

Imports System.Web

Public Class ServerTimeClient

Private timeServer As localhost.Service

Dim cookies As CookieCollection

Dim keyword As String

Dim value As String

Private Sub btnGetTime_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnGetTime.Click

Dim i As Integer

Dim serverUri As System.Uri = Nothing

Dim cookieString As String = ""

Uri.TryCreate(timeServer.Url(), UriKind.Absolute, serverUri)

tbDisplayTime.Text = timeServer.GetTheTime()

cookies = timeServer.CookieContainer.GetCookies(serverUri)

If ((cookies Is Nothing) = False) Then

For i = 0 To cookies.Count - 1

cookieString &= cookies(i).ToString()

End If

If (cookieString <> "") Then

MsgBox(cookieString)

End If

End Sub

Public Sub New()

' This call is required by the Windows Form Designer.

InitializeComponent()

' Add any initialization after the InitializeComponent() call.

timeServer = New localhost.Service()

timeServer.CookieContainer = New CookieContainer()

End Sub

Private Sub ServerTimeClient_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

End Sub

End Class

Miscellaneous Defaults

Local projects

http://localhost

Using IIS the default directory is c:\InetPub\wwwroot