2.ASP.NET Server Controls - ASP.NET Web Forms
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This is presentation about ASP.NET Server Controls, part of the free ASP.NET Web Forms Course in Telerik Academy. Telerik Software Academy: http://aspnetcourse.telerik.com The website and all video materials are in Bulgarian Table of contents: Controls Class Hierarchy; HTML Server Controls; Web Server Controls; Web Server Control Life Cycle; HTML escaping; ASP.NET server controls; Example of ASP.NET server controls; ASP.NET Web Forms Course @ Telerik Academy http://aspnetcourse.telerik.com
Transcript of 2.ASP.NET Server Controls - ASP.NET Web Forms
ASP.NET Server Controls
Web Controls. HTML Controls.HTML Escaping
Svetlin Nakov
Telerik Software Academyacademy.telerik.com
Technical Trainerwww.nakov.com
aspnetcourse.telerik.com
Table of Contents1. Controls Class Hierarchy
2. HTML Server Controls
3. Web Server Controls Basic Web Controls Validation Controls List Controls Rich Controls
4. Web Server Control Life Cycle
5. HTML Escaping2
What is ASP.NET Server Control?
ASP.NET server controls The smallest ASP.NET Component Wrap an HTML UI element, or more
complex UI Component-oriented programming
model Executed and rendered at the
server side Example of ASP.NET server controls: <asp:Button> <input type="submit">
<asp:Label> <span> <asp:GridView> <table><tr><td>…
3
What is ASP.NET Server Control ?
(2) Mandatory properties for all server controls: runat="server" ID="…"
Programming model based on events Each user interaction causes and
event
Programmer decides which events to handle
Browser-specific HTML is generated Controls deliver appropriate HTML
depending on browser type
4
Controls – Class Hierarchy
Controls – Class Hierarchy
System.Web.UI.Control Base for all controls
Properties – ID, Page, ViewState, Context, ClientID, Controls
Methods – Render(HtmlTextWriter writer)
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Controls – Class Hierarchy (2)
System.Web.UI.HtmlControls.HtmlControl
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Controls – Class Hierarchy (3)
System.Web.UI.WebControls.WebControl
System.Web.UI.TemplateControl
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HTML Server Controls
HTML Server Controls HTML server controls are very simple
extension of Control class Look like traditional HTML
Defined by runat="server"
Simple HTML seems like text on the server
If an HTML element is converted to HTML server control, a server side object is associated with it
Valid only inside a Web form tag:
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<form runat="server">…</form>
HTML Server Control – Example
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<%@ Page Language="C#" %><script language="c#" runat="server"> void ButtonSubmit_Click(Object sender, EventArgs e) { Response.Write("Value:<b>"+TextField.Value+"</b>"); }</script><html><head><title>HTML Server Controls</title></head><body> <form id="formMain" runat="server"> <input id="TextField" type="text" runat="server" /> <input id="ButtonSubmit" type="button" runat="server" value="Submit" onserverclick="ButtonSubmit_Click" /> </form></body></html>
HTML Server Controls
Live Demo
HTML Server Control Classes
HtmlForm – <form>…</form> HtmlInputText – <input type="text">
HtmlButton – <input type="button" />
HtmlAnchor – <a href="…">…</a>
HtmlSelect – <input type="select"> HtmlTable, HtmlTableCell, HtmlTableRow – <table><tr><td>…</td></tr></table>
HtmlImage – <img src="…" /> ...
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HTML Server Control Classes (2)
HtmlGenericControl Used for all other HTML elements
<p> <div> <span> <meta> <body> …
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HtmlGenericControl – Example
15
<%@ Page Language="C#" %>
<script runat="server"> void Page_Load(Object sender, EventArgs e) { this.MetaInfo.Attributes["name"] = "description"; this.MetaInfo.Attributes["content"] = "The page was
generated on: " + DateTime.Now.ToString();}
</script>
<html><head> <meta id="MetaInfo" runat="server" /> </head><body> <form id="formMain" runat="server">…</form></body></html>
HTML Generic Controls
Live Demo
Web Server Controls
Web Server Controls
Web server controls are server UI controls that abstract the common HTML elements Have own lifecycle and functionality
Come with .NET Framework Located in System.Web.UI.WebControls namespace, inherit from the WebControl class
HTML Abstraction Rendered HTML tags are quite different from the design-time markup
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Web Server Controls – Features
Rich functionality
Type-safe programming capabilities
Automatic Web browser detection
AutoPostBack
Sumbit when the focus is lost
Support for themes
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Web Server Controls - Syntax
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tag_prefix determines
unique namespace for
the web control
The name of the control
Attributes are properties of
the Web control
Mandatory attribute
runat="server"
<tag_prefix:controlname attributes runat="server"/>
Web Server Control – Example
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<form id="formMain" runat="server"> <asp:Label ID="LabelResult" runat="server" Text="" Visible="false" /> <asp:TextBox ID="TextBoxInput" runat="server" /> <asp:Button ID="ButtonSubmit" runat="server" Text="Submit" OnClick="ButtonSubmit_Click" /></form>…protected void ButtonSubmit_Click( object sender, EventArgs e){ this.LabelResult.Text = "You entered: " + this.TextBoxInput.Text; this.LabelResult.Visible = true;}
Web Server ControlsLive Demo
System.Web.UI. WebControls.WebContr
ol The WebControl class defines properties, events and methods for all Web controls
Control the appearance BackColor ForeColor BorderWidth BorderStyle BorderColor
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System.Web.UI. WebControls.WebControl
(2) Control the behavior
Enabled Visible TabIndex ToolTip …
Not all controls support all these properties See the documentation for details
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Web Server ControlsBasic Web Controls
Basic Web Controls HTML
<asp:button> <input type="submit"><asp:checkbox> <input type="checkbox"><asp:hyperlink> <a href="…"></a><asp:image> <img src="…"><asp:imagebutton>
<input type="image">
<asp:linkButton>
<a href="…"></a>
<asp:label> <span>…</span><asp:listbox> <select
size="5"></select><asp:panel> <div>…</div><asp:radiobutton>
<input type="radio">
<asp:table> <table>…</table><asp:textbox> <input type="text">
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Basic Web Controls: TextBox
Creates single-line or multiline text-box
Lets the user to enter text Properties
Text TextMode – SingleLine, MultiLine, Password
MaxLength ReadOnly AutoPostBack
Events TextChanged – combined with AutoPostBack
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Basic Web Controls: Label
Display static text in a <span> block Allows programmatically to manipulate it
Properties Text
AssociatedControlID – on click focus goes to the specified control
Events TextChanged – combined with AutoPostBack
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CAUTION: the Text is NOT HTML encoded before it is displayed in the Label control. This make it possible to embed script within
HTML tags in the text.
Basic Web Controls: Literal
Display static text Allows programmatically to manipulate it Unlike the Label control, Literal
does not let you apply styles to its content
Properties Text
Renders the Text property value directly
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CAUTION: the Text is NOT HTML encoded before it is displayed in the Literal control. This make it possible to embed script within
HTML tags in the text.
Basic Web Controls – Buttons
Implement IButtonControl Properties
Text – button's title
CommandName – pass a command
CommandArgument – pass command arguments
PostBackUrl – posts back to specified page
CausesValidation – perform validation or not
ValidationGroup – which validation group to be validated
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Basic Web Controls – Buttons (2)
Events Click Command
CommandName and CommandArgument are passed to code behind
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Basic Web Controls – Buttons (3)
Different button types Button
Creates a push button
Submit button by default
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Basic Web Controls – Buttons (4)
Different button types Command Button
Has command name associated (CommandName property)
Programmatically determine which button is clicked in Command event handles
Used in templated controls, e.g. GridView
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Basic Web Controls – Buttons (5)
Different button types LinkButton
Same functionality as Button
Renders as hyperlink
Use Hyperlink if you want to link to another page
Renders JavaScript on the client browser
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Basic Web Controls – Buttons (6)
Different button types ImageButton
Display an image that responds on mouse click
ImageURL – URL to displayed image
Both Click and Command events are raised
35
Buttons – Example
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<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Buttons.aspx.cs" Inherits="Buttons" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head runat="server"> <title>Untitled Page</title></head><body> <form id="formMain" runat="server"> <asp:Button ID="ButtonEx" CommandName="ButtonEx" runat="server" OnClick="OnBtnClick" OnCommand="OnCommand" Text="Normal Button" /> <br />
Buttons – Example (2)
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<asp:LinkButton ID="LinkButtonEx" runat="server" OnClick="OnBtnClick" Text="Link Button" CommandName="LinkButtonEx" OnCommand="OnCommand" /> <br /> <asp:ImageButton ID="ImageButtonEx" runat="server" CommandName="ImageButtonEx" ImageUrl="~/images/DotNet_Logo_Small.gif" OnCommand="OnCommand" OnClick="OnBtnClick" /> <br /> <asp:Label ID="LabelMessage" runat="server" Text=""></asp:Label> </form></body></html>
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ButtonsLive Demo
Basic Web Controls – Panel
The Panel control Container for other controls
Rendered as <div>
Useful for: Displaying and hiding groups of
controls
Generating and inserting controls at runtime
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Basic Web Controls – Panel(2)
Properties ScrollBars – modify visibility and
position of scroll bars
Wrap – value indicating whether the content wraps within the panel
GroupingText – caption for the group of controls that is contained in panel control
DefaultButton – button to be pressed by default (Enter)
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PanelsLive Demo
Basic Web Controls – PlaceHolder
The PlaceHolder control Reserves a space in the page control hierarchy Used to add controls to the page at
runtime
Does not produce any visible output
Controls Use it to add, insert or remove
controls from PlaceHolder Control42
Basic Web Controls – CheckBox
Select between checked / unchecked
Properties Checked Text – control caption
AutoPostBack automatically posts back the page
when control state is changed
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Basic Web Controls – CheckBox (2)
CausesValidation – whether validation is performed
ValidationGroup – which validation group to be validated
Events CheckChanged
44
Basic Web Controls – RadioButton
Creates a radio button on the Web Forms page
Properties Text GroupName – allow a mutually
exclusive selection from the group
45
Validation ControlsPerforming Control Validation
Validation Controls The ASP.NET Web forms validation controls Validate the values that are entered
into other controls of the page Two modes of validation
Client-side validation Server-side validation
Validation is performed at page submit
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Validation Controls (2) Most important validation controls:
RequiredFieldValidator RangeValidator CompareValidator RegularExpressionValidator CustomValidator ValidationSummary
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Validation Controls
Live Demo
List ControlsDisplaying Lists of Items
List Controls List Web controls
Display list of items, e.g. table of rows
Support binding to a collection
Display rows of data in templated format
Expose DataSourceID, DataSource, DataMember properties
Bind to collection that support IEnumerable, ICollection or IListSource
51
List Controls (2) ListBox CheckBoxList RadioButtonList Repeater DataList GridView DropDownList
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List ControlsLive Demo
Web Server ControlsRich Controls
Rich Controls Task-specific controls Built with multiple HTML elements Rich functionality Examples:
Calendar AdRotator
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Web Server
Controls – Lifecycle
Phases Init ViewState Load Send Postback Change Notification Handle Postback events PreRender Save State Render Dispose Unload
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Phases - Initialize
Control initialize settings needed during incoming web request
Init event (OnInit method)
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Phases – Load View State
At the end of this phase ViewState property is automatically populated
Override LoadViewState method to customize state restoration
LoadViewState method
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Phases – Load Perform actions common to all requests
Server controls in the tree are created and initialized
Control state from previous round trip is restored including client – side data
Load event (OnLoad method)
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Phases – Send Postback Change Notification
Raise change events in response to state changes between previous and current postbacks
RaisePostDataChangedEvent method IPostBackDataHandler should be implemented
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Phases – Handle Postback Events
Handle client-side events caused postback
Raise appropriate events on the server
RaisePostBackEvent method IPostBackEventHandler should be implemented
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Phases – PreRender Perform any updates before the control is rendered
Changes made in this phase can be saved
PreRender event (OnPreRender method)
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Phases – Save State ViewState property is persisted Send to the client and back as a hidden field
SaveViewState method
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Phases – Render Generates the output which will be send to the client
Any changes to controls state made here are lost
Render() method
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Phases – Dispose Final clean up Expensive resources should be released
Dispose() method
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Phases – Unload Final clean up Usually clean up is performed in previous phase so this event is not handled
UnLoad event (OnUnLoad() method)
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Controls Lifecycl
eLive Demo
HTML Escaping
What is HTML Escaping?
HTML escaping is the act of replacing special characters with their HTML entities Escaped characters are interpreted
as character data instead of mark up
Typical characters to escape <, > – start / end of HTML tag
& – start of character entity reference
', " – text in single / double quotes
…
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Character Encoding Each character could be presented as
HTML entity escaping sequence Numeric character references:
'λ' is λ, λ or λ Named HTML entities:
'λ' is λ '<' is < '>' is > '&' is & " (double quote) is "
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XSS Attack Cross-site scripting (XSS) is a common security vulnerability in Web applications Web application is let to display a
JavaScript code that is executed at the client's browser Crackers could take control over
sessions, cookies, passwords, and other private data
How to prevent from XSS? ALWAYS validate the user input
Perform HTML escaping when displaying text data in a Web control
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What Offers ASP.NET? ValidateRequest attribute of Page directive Checks all input data against a
hard-coded list of potentially dangerous values
The default is true
Using it could harm the normal work on some applications E.g. a user posts JavaScript code in a
forum
Escaping is better way to handle the problem!
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What Offers ASP.NET ? (2)
HttpServerUtility.HtmlEncode
HTML encodes a string and returns the encoded string
Page.Server is instance of HttpServerUtility
The following script
Output:
Web browser renders the following:
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<%response.write(Server.HTMLEncode("The image tag: <img>"))%>
The image tag: <img>
The image tag: <img>
HTML EscapingLive Demo
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