Web Forms

Delivering Excellence in Software Engineering

® 2006. EPAM Systems. All rights reserved.

Web Forms


Objectives

• Introduce Web Forms– Control-based programming model

• Present server side controls– Html controls– Web controls

• Discuss tools for building web forms– Visual Studio 2005/2008


Control-based programming

• Control-based programming is a familiar paradigm– Desktop application development

libraries have used control-based programming for years

– A program consists of a collection of controls

– Each control knows how to render its state to the screen

– The developer manipulates the state of these controls and lets rendering happen implicitly


ButtonID="Button1"Text="Enter"Location=(104,48)Draw()

MenuID="Menu1"Items[] = {"File", "Help" }IDs[] = { ID_FILE, ID_ABOUT }Draw()

TextBoxID="tb1"Text=""Location=(104,16)Draw()

LabelID="lb1"Text="Name:"Location=(8,16)Draw()

Visual Rendering

Programmatic Elements

Window.TextOut(...)

Window.TextOut(...)

Window.Rectangle(...)

Window.Rectangle(...)

Conceptual model for control-based programming


Control-based programming for web applications

• ASP.NET brings control-based programming to web apps– Server-side objects created to represent

elements of a page– Each server-side object capable of

rendering itself as HTML– Layered on top of Request/Response

architecture of HTTP– Some desktop paradigms work well– Others must be re-thought


ButtonID="Button1"Text="Enter"Render()

ToolbarID="tb1"Items[] = {"File", "Help" }Render()

TextBoxID="tb1"Text=""Render()

LabelID="lb1"Text="Name:"Render()

Visual Rendering

Programmatic Elements

<tbns:ToolBar ...>

<span>Name:</span>

<input type=text/>

<input type=submit value='Enter'/>

Conceptual model for web forms applications


Server-side controls

• The web forms model is based on a set of primitive controls– Called server-side controls as they exist

on the server and provide rendering to the client as HTML

– Created using runat=server attribute on traditional HTML elements in a .aspx page

– Can be referenced within server-side code using designated ID

– Implicitly added as member variables to the generated Page-derived class definition


<%@ Page Language="C#" %><html>

<body> <form runat="server" > Enter name: <input type="text" id="_name" runat="server" /> <br/> Personality: <select id="_personality" runat="server" > <option>extraverted</option> <option>introverted</option> <option>in-between</option> </select> <input type="submit" value="Submit" /> <p> <% if (IsPostBack) {%> Hi <%=_name.Value%>, you selected <%=_personality.Value%> <% } %> </p> </form></body></html>

An ASP.NET page using server-side controls<%@ Page Language="C#" %>

<% %><% %><% %>

<% %>


using System.Web.UI;using System.Web.UI.HtmlControls;using System.Web.UI.WebControls;

public class WebFormPage1_aspx : Page{ protected HtmlInputText _name; protected ListItem __control3; protected ListItem __control4; protected ListItem __control5; protected HtmlSelect _personality; protected HtmlForm __control2; // ...}

Generated Page-derived class with server-side controls


Server-side control state management

• Server-side controls must manage their state– Initial GET request to a page creates the

server side controls with their default values

– Subsequent POST requests back to the same page creates the server side controls with the values in the POST body

– Any changes made to the value of the controls during the processing of a request will be reflected when the page is rendered


ClientServer

page1_aspx instance #1

_name.Value_personality.Value

""""

page1_aspx instance #2

_name.Value_personality.Value

"Sam""introverted"

GET /test/page1.aspx HTTP/1.1submit request

HTTP/1.1 200 OK... <html> ... <input id="_name" type="text" />

renders

response returned

client interaction

POST /test/page1.aspx HTTP/1.1..._name=Sam&_personality=introverted

submit pressedsubmit request

HTTP/1.1 200 OK... <html> ... <input id="_name" type="text" value="Sam" />...

renders

response returned

WebForm Client Interaction


Server Control Behaviors

• Server controls retain their state between POST requests back to the same page– No need to re-initialize state on POST-

back requests– Can not be used for cross-page POST

requests– Controls that are not intrinsically

included in a POST request have their state propagated via a hidden field (ViewState)• More on this later


HtmlControls

• HtmlControls are server-side representations of standard HTML elements– Any HTML element in an ASPX page

marked with the runat=server attribute will become an HTML control on the server

– All derive from HtmlControl class– HTML elements with no distinguished

server-side functionality (like div, span, etc.) are all represented as HtmlGenericControl instances


System.Object

System.Web.UI.Control

HtmlControl

HtmlImage

HtmlInputControl

HtmlInputFile

HtmlInputHidden

HtmlInputImageHtmlInputRadioButton

HtmlInputText

HtmlInputButtonHtmlInputCheckBox

HtmlContainerControl

HtmlForm

HtmlGenericControl

HtmlSelectHtmlTable

HtmlTableCell

HtmlTableRowHtmlTextAreaHtmlAnchorHtmlButton

<table>

<form>

<input type=button>

<tr>

<td>,<th>

<input type=text><textarea>

<input type=image>

<input type=file>

<input type=hidden>

<input type=radio>

<input type=checkbox>

<select>

<a>

<span>,<div>, ...

<button>

<img>

Hierarchy of HtmlControls and the tags they map to



<body> <form runat="server"> <input type="radio" runat="server">click me</input><br/> <input type="checkbox" runat="server">check me</input><br/> <input type="button" value="Push me" runat="server" /><br/> <input type="text" value="type in me" runat="server" /><br/> <table runat="server"> <tr><td>cell00</td><td>cell01</td></tr> <tr><td>cell10</td><td>cell11</td></tr> </table> </form></body></html>

A sample ASP.NET page written with HtmlControls

<%@ Page Language="C#" %>


WebControls

• WebControls provide a more consistent object model and a higher level of abstraction than HtmlControls– Most HTML elements can also be represented as WebControls on the server

– WebControl versions typically have a more consistent interface (background color is always BackColor property whereas in HTML it may be a style attribute (span) or a property (table) )

– WebControls also provide higher-level controls with more functionality than primitive HTML elements (like the Calendar control)

– WebControls may render themselves differently based on client browser capabilities


Syst em. Obj ectSyst em. Web. UI . Cont r ol

WebCont r olAdRot at orBaseDat aLi st

Dat aGr i dDat aLi stBut t on

Cal endarCheckBoxRadi oBut t on

Hyper Li nk

I mageI mageBut t on

LabelBaseVal i dat or

BaseCompar eVal i dat or

Cust omVal i dat orRangeVal i dat or

Regul ar Expr essi onVal i dat orRequi r edFi el dVal i dat or

Li nkBut t onLi st Cont r ol

Radi oBut t onLi stCheckBoxLi stDr opDownLi st

Li st BoxPanelTabl e

Tabl eCel lTabl eHeader Cel l

Tabl eRowText Box

Val i dat i onSummar y

Repeat er

Compar eVal i dat or

Xml

Hierarchy of WebControls



<body> <form runat="server"> <asp:RadioButton Text="click me" runat="server" /><br/> <asp:CheckBox Text="check me" runat="server" /><br/> <asp:Button Text="Push me" runat="server" /><br/> <asp:TextBox Text="type in me" runat="server" /><br/> <asp:TextBox TextMode="MultiLine" rows="3" Text="type more in me" runat="server" /><br/> <asp:Table runat="server"> <asp:TableRow> <asp:TableCell>cell00</asp:TableCell> <asp:TableCell>cell01</asp:TableCell> </asp:TableRow> <asp:TableRow> <asp:TableCell>cell10</asp:TableCell> <asp:TableCell>cell11</asp:TableCell> </asp:TableRow> </asp:Table>

</form></body></html>

A sample ASP.NET page written with WebControls<%@ Page Language="C#" %>


Page Lifecycle

• Each request to a page results in a new instance of that class– Page state is not retained between requests

• Several events defined by the Page class– Useful to define handlers in code-behind classes– 4 events called in sequence during a page's lifetime– Possible to subscribe to these events in three ways

• Explicitly subscribing a delegate to the event• Overriding virtual function handlers in base class• Defining functions named Page_xxx with AutoEventWireup set to true


public class Page : TemplateControl, IHttpHandler{ // Events public event EventHandler Init; public event EventHandler Load; public event EventHandler PreRender; public event EventHandler Unload;

// Pre-defined event handlers protected virtual void OnInit(EventArgs e); protected virtual void OnLoad(EventArgs e); protected virtual void OnPreRender(EventArgs e); protected virtual void OnUnload(EventArgs e);}

Events in the Page class


public class EventsPage : Page{

// Override OnInit virtual function to manually// subscribe a delegate to the Load eventprotected override void OnInit(EventArgs e){

this.Load += new EventHandler(MyLoadHandler); base.OnInit(e);

}

// Load event handlerprotected void MyLoadHandler(object src, EventArgs e){

Response.Write("<tiny>rendered at top of page</tiny>");}

}

Example: Adding event handlers using virtual function overriding and manual delegate subscription

<%@ Page Language='C#' AutoEventWireup='true' %>

<script runat="server"> protected void Page_Load(object src, EventArgs e) { Response.Write("<h4>Load event fired!</h4>"); }</script>

<html><body><h1>AutoEventWireup Page</h1></body></html>

Example: Adding event handlers using AutoEventWireup

defaults to true

<%@ Page Language='C#' AutoEventWireup='true' %>


Server-side control state initialization

• The Load event of the Page class is commonly where control state is initialized– Invoked after controls have been created, but before

rendering– Because controls retain their state across POST

requests, it is usually only necessary to initialize their state once// Common control interactionif (!IsPostBack) initialize control stateelse look at/process client-submitted state


Sample Page Initializing Control State In OnLoad

<%@ Page Language="C#" %><script runat="server">protected override void OnLoad(EventArgs e) {

if (!IsPostBack) {

_lb.Items.Add(new ListItem("item 1"));_lb.Items.Add(new ListItem("item 2"));_lb.Items.Add(new ListItem("item 3"));_lb.Items.Add(new ListItem("item 4"));

}else

_message.Text = string.Format("You selected {0}", _lb.SelectedItem.Text);

base.OnLoad(e);}</script><html> <body> <form runat=server> <asp:ListBox id="_lb" runat="server" /><br> <asp:Label id="_message" runat="server" /><br> <input type=submit value="Submit" /></form></body></html>



Events

• Many server-side controls can generate server-side events– Exposed as standard CLR EventHandler delegates– To subscribe to an event of a server-side control

• Construct a new instance of the EventHandler delegate• Initialize it with your handler function pointer• Subscribe the delegate to the control's event

– Alternatively, you can subscribe to an event by• Indicating your handler function with the OnEvent attribute in

the control's tag



<html><script runat="server">protected void OnClickMyButton(object src, EventArgs e){

_message.Text = "You clicked the button!"; }protected override void OnInit(EventArgs e){

_MyButton.Click += new EventHandler(OnClickMyButton); base.OnInit(e);}</script><body> <form runat="server"> <h2>ASP.NET event page</h2> <p> <asp:Button id="_MyButton" Text="Click me!" runat="server" /> </p> <asp:Label id="_message" runat="server" /> </form></body></html>

Server-side event handler using explicit delegate subscription




<html><script runat="server">protected void OnClickMyButton(object src, EventArgs e){

_message.InnerText = "You clicked the button!"; }</script><body> <form runat="server"> <h2>ASP.NET event page</h2> <p> <input type="button" id="_MyButton" value="Click me!" OnServerClick="OnClickMyButton" runat="server" /> </p> <span id="_message" runat="server" /> </form></body></html>

Server-side event handler using OnEvent syntax



Events in the Page Lifecycle

• Events are issued after the Load event, but prior to rendering

• Very common control interaction is:– In Load event handler, initialize control

state (when IsPostBack is False)– In server-side event handlers for

controls (OnButtonClick...), process client-submitted state


<%@ Page Language="C#" %><script runat="server">protected override void OnLoad(EventArgs e) {

if (!IsPostBack) {_lb.Items.Add(new ListItem("item 1"));_lb.Items.Add(new ListItem("item 2"));_lb.Items.Add(new ListItem("item 3"));_lb.Items.Add(new ListItem("item 4"));

} base.OnLoad(e);}protected void OnEnter(object src, EventArgs e) {

_message.Text = string.Format("You selected {0}", _lb.SelectedItem.Text);}</script><html> <body> <form runat=server> <asp:ListBox id="_lb" runat="server" /><br> <asp:Label id="_message" runat="server" /><br> <input type="button" value="Enter" OnServerClick="OnEnter" /></form></body></html>

Server-side event with control state interaction



Page event sequencing

• It is critical to understand the event sequencing of the Page– Pages are created and discarded with each request– There is an explicit, deterministic sequences of events

that occurs with the lifetime of each page– It is important to know where in that sequence you

should perform tasks• When can I look at a control's contents?• When can I modify a control's contents?• When is the Request object available?• ...


IHttpHandler.ProcessRequest method ofPage class invoked

Page-derived class is created,constructor is invoked

POST Request issued by client

Init event of Page class fires

virtual CreateChildControls method ofPage is invoked

Server-side control state is restored from POSTvariables and VIEWSTATE

Load event of Page class fires

Server-side control events are fired

PreRender event of Page class fires

virtual Render method of Page class invoked

virtual RenderChildren method ofPage class invoked

Unload event of Page class fires

instance of Page-derived class is discarded

HTTP Response issued to client

Page POST-back event sequence


Web Forms and Code-behind

• Server-side controls in combination with code-behind enables true separation of page logic from page layout and rendering– Server-side controls must be declared in code-behind

class as public or protected variables with names matching control IDs

– During parsing of the .aspx page, ASP.NET will look for member variables with matching names in the base class• If it finds a variable of the appropriate type, it will use it• Otherwise it will create a new member variable in the .aspx-

generated class definition


<%@ Page Language="C#" Inherits="Page2" Src="Page2.cs" AutoEventWireUp="false" %><html><body>

<form runat="server"><h3>Enter name: <asp:TextBox id="_name" runat="server"/></h3><h3>Personality: <asp:DropDownList id="_personality" runat="server" /></h3><asp:Button id="_enterButton" Text="Enter" runat="server"/><asp:Label runat="server" id="_message" />

</form></body></html>

Page with server-side controls using code-behind

<%@ Page Language="C#" Inherits="Page2" Src="Page2.cs" AutoEventWireUp="false" %>


public class Page2 : Page{

protected HtmlSelect _personality;protected HtmlInputText _name;protected HtmlInputButton _enterButton;protected HtmlGenericControl _messageParagraph;

override protected void OnInit(EventArgs e){ _enterButton.ServerClick += new EventHandler(OnEnter); }

override protected void OnLoad(EventArgs e){

if (!IsPostBack){

_personality.Items.Add(new ListItem("extraverted"));_personality.Items.Add(new ListItem("introverted"));_personality.Items.Add(new ListItem("in-between"));

}}

protected void OnEnter(object src, EventArgs e){

string msg = string.Format("Hi {0}, you selected {1}",_name.Value, _personality.Value);_messageParagraph.InnerText = msg;

}}

Code-behind file for server-side control page


Web Forms Applications with Visual Studio .NET

• Visual Studio .NET supports creating Web projects– Generates new virtual directory for your project– Project output is a single assembly containing all code-

behind, deployed in the /bin directory– Designer support for WebForms with automatic code-

behind updates– Wizards for standard web components (web forms, user

controls, etc.)• Standard ClassLibrary projects can be used to create

ASP.NET applications as well


Web Form Generation

Codebehind attribute used by VS.NET to associatecode-behind file with .aspx file (not equivalent to src=)


Code-behind for VS.NET WebForm

namespace WebFormsApp { public class WebForm1 : Page { protected Button _PushMe; protected TextBox _Name; private void Page_Load(object sender, EventArgs e) { // Put user code to initialize the page here }#region Web Form Designer generated code override protected void OnInit(EventArgs e) { InitializeComponent(); base.OnInit(e); } private void InitializeComponent() { _PushMe.Click += new System.EventHandler(Button1_Click); this.Load += new System.EventHandler(this.Page_Load); }#endregion private void Button1_Click(object sender, EventArgs e) { } }}

OnInit override with call toInitializeComponent

Explicit eventwire-up

Server-controlmember variables

Load event handler


Summary

• ASP.NET brings control-based programming to web development

• Server-side controls retain state between post-backs

• HtmlControls provide server-side equivalents of HTML elements

• WebControls provide more consistent object model for server-side controls, as well as some more sophisticated controls

Delivering Excellence in Software Engineering


For more information, please contact:

Uladzimir TsikhonSoftware Engineering Manager, Belarus Recourse Development DepartmentEPAM Systems, Inc.Belarus, MinskPhone: +375(17) 2101662 ext 1756Fax: +375(17) 2101168Email: [email protected]://www.epam.com

Web Forms

Documents

Transcript of Web Forms