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ptg 1774 points during an application’s execution. The $(document).ready() event fires when the Domain Object Model (DOM) is loaded. Generally, you can put most of your jQuery code in this event: $(document).ready(function() { // your jQuery code goes here } By doing so, you’re ensuring that your page is ready before it runs your code. Otherwise, your logic might start executing before the page has completed loading, and your code might not work as expected. In Listing 40.2, our script tells the browser to execute the sayMessage() method when the document is ready. When you execute the page, you can see the alert box pop up as soon as you open the page. Although it appears to pop up right away, the browser is actually waiting until any other page-preparing logic has completed and is ensuring that the DOM is fully loaded. When those conditions are met, the code in $(document).ready() fires and you see the alert box. jQuery Selectors Selectors are a core piece of the jQuery library. jQuery code follows this basic methodology: Select an element. Do something with it. As we mentioned above, the $() is the method that you use to select elements. For $(document).ready(), we’re actually selecting the “document” and defining what to do when the ready() event fires. You can select any element (or multiple elements) on your page. Following are three basic ways of selecting elements: . By ID—Matches a single element with the element ID. The ID you provide should be prefaced by a # character. For example, $(“#myId”) would match <div id=”myId”>. . By CSS Class—Matches all elements with the provides CSS class. The class you provide should be prefaced with a . character. For example, $(“.navigationListItem”) would match <li class=”navigationListItem”>. . By Element—Matches all elements by tag name. For example, $(“div”) would match <div id=”myId1”> and <div id=”myId2”>. CHAPTER 40 Client-Side AJAX with jQuery From the Library of Wow! eBook ptg 1775 What Is jQuery? 40 After selecting an element (or elements), you need to do something with it. For example, you can define what should execute when you click an element by using the ”click” function. Listing 40.3 demonstrates this: LISTING 40.3 jqueryClick.js /// <reference path=”/Scripts/jquery-1.4.1.js”/> function spanClicked() { $(“#colorSpan”).addClass(“redClass”); } $(document).ready(function () { $(“#clickSpan”).click(spanClicked); }); This code has two sections of jQuery. First, we define a function called ”spanClicked” that selects the element with the ID ”colorSpan”. It then adds a CSS class to that element called ”redClass”Second, we define the $(document).ready() code. When the document finishes loading, we select the element with an ID of ”clickSpan” and tell it to execute the ”spanClicked” function whenever that element is clicked. Notice how we use inline function()syntax in the $(document).ready code. This is called an anonymous function in JavaScript and enables you to define functions inside of your logic without needing to explicitly define and name it. It is often used with jQuery and enables you to nest all your logic in a single call instead of defining a method for each one. It dramatically improves the readability and fluidity of your code as well. The page in Listing 40.4 defines the span elements along with the CSS class and demon- strates the jQuery selectors. LISTING 40.4 jqueryClick.aspx <%@ Page Language=”C#” %> <!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Transitional//EN” “http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd”> <script type=”text/javascript” src=”./Scripts/jquery-1.4.1.js”></script> <script type=”text/javascript” src=”./Scripts/jqueryClick.js”></script> <html xmlns=”http://www.w3.org/1999/xhtml”> <head id=”Head1” runat=”server”> <title></title> From the Library of Wow! eBook ptg 1776 <style type=”text/css”> .redClass { color: Red; } </style> </head> <body> <form id=”form1” runat=”server”> <div> <p><span id=”clickSpan”>This is the span that we will click.</span></p> <p><span id=”colorSpan”>This will turn red when we click on it.</span></p> </div> </form> </body> </html> There is an amazing amount of events and functions available in jQuery to apply to your selected objects. For a complete list, visit the documentation and tutorial sections at http://www.jquery.com. Calling Web Services from the Client The heart of Ajax is the capability to send and retrieve information from the web server without needing to post back a page to the web server. Ajax is all about performing “sneaky” postbacks. The vision behind a pure Ajax application is that it should consist of a single page. All updates to the single page after it has been loaded should be performed by calling web services. You should never need to perform a postback because any postback results in a bad user experience. (The page jumps and the universe freezes.) The jQuery library provides support for calling web services directly from the client (the web browser) with a built-in function called $.ajax. In this section, you learn two methods of exposing a web method to an AJAX page. You learn how to call a web method from a separate web service and how to call a web method exposed by the page. Calling an External Web Service Let’s start simple. We create a Quotation web service that randomly returns a quotation from a list of quotations. Next, we create an AJAX page that contains a button. When you click the button, a random quotation displays in a <span> tag (see Figure 40.4). CHAPTER 40 Client-Side AJAX with jQuery From the Library of Wow! eBook ptg 1777 Calling Web Services from the Client 40 FIGURE 40.4 Retrieving a random quotation from the server. The first step is to create the web service, which is contained in Listing 40.5. LISTING 40.5 QuotationService.asmx <%@ WebService Language=”C#” Class=”QuotationService” %> using System; using System.Web; using System.Web.Services; using System.Web.Services.Protocols; using System.Web.Script.Services; using System.Collections.Generic; [WebService(Namespace = “http://tempuri.org/”)] [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)] [ScriptService] public class QuotationService : System.Web.Services.WebService { [WebMethod] public string GetQuote() { List<string> quotes = new List<string>(); quotes.Add(“The fool who is silent passes for wise.”); quotes.Add(“The early bird catches the worm.”); From the Library of Wow! eBook ptg 1778 quotes.Add(“If wishes were true, shepherds would be kings.”); Random rnd = new Random(); return quotes[rnd.Next(quotes.Count)]; } } You create the file in Listing 40.5 by selecting Website, Add New Item and choosing the Web Service item. The web service contains a single web method named GetQuote(). This method returns a single quotation from a list of quotations as a string. There is only one thing special about this web service. A ScriptService attribute is applied to the web service class. (The ScriptService attribute lives in the System.Web.Script.Services namespace.) You must add this attribute to call the web service from an AJAX page. Now that we have created the web service, we can call it from an AJAX page. The page in Listing 40.6 calls the web service to display a random quotation. LISTING 40.6 ShowWebServiceMethod.aspx <%@ Page Language=”C#” %> <!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 id=”Head1” runat=”server”> <title>Show Web Service Method</title> <script type=”text/javascript” src=”./Scripts/jquery-1.4.1.js”></script> <script type=”text/javascript”> $(document).ready(function () { $(“#btnGet”).click(function () { $.ajax({ type: “POST”, dataType: “json”, contentType: “application/json”, url: “QuotationService.asmx/GetQuote”, success: function (data) { $(“#spanQuote”).html(data.d); }, error: function () { alert(“The call to the web service failed.”); } CHAPTER 40 Client-Side AJAX with jQuery From the Library of Wow! eBook ptg 1779 Calling Web Services from the Client 40 }) }); }); </script> </head> <body> <form id=”form1” runat=”server”> <div> <input id=”btnGet” type=”button” value=”Get Quote” /> <br /><br /> <span id=”spanQuote”></span> </div> </form> </body> </html> You should note several things in this page. To begin, the first thing we do in the $(document).ready() call is add a click event handler to the ”btnGet” element. This click event makes one function call to the $.ajax function. The $.ajax jQuery function makes an asynchronous call to a URL. In this case, we call the web service method that we defined at QuotationService.asmx/GetQuote. If this asynchro- nous call is successful, the “success” parameter’s function gets called, which selects the “spanQuote” and fills it with the data that was returned by using the “html” jQuery function. We also pass in a data type and content data type of “json” to our web service. JSON stands for JavaScript Object Notation and is a lightweight format that enables you to define an unordered set of name/value pairs. This data is contained in the ”d” property of data—when we call the ”html” jQuery function, we pass in ”data.d” as the parameter so all the data is pushed into the span. When web services first started being utilized, XML was used almost exclusively to send data back and forth. Today, JSON is quickly becoming the standard because large amounts of data can be sent back and forth without the extra overhead of XML. When you call a web method with $.ajax, you can pass a reference to both a success and an error method. If the web method call is successful, the success method is called. Otherwise, the error method is called. In Listing 40.6, if the $.ajax call is successful, the quotation displays in a <span> tag in the body of the page. From the Library of Wow! eBook ptg 1780 CHAPTER 40 Client-Side AJAX with jQuery Calling a Static Page Method If you do not plan to call a web method from multiple pages, don’t perform all the work of creating a separate web service. Instead, you can expose a static method from the same AJAX page calling the web method. For example, the page in Listing 40.7 includes a server method named GetQuote(). LISTING 40.7 ShowPageMethod.aspx <%@ Page Language=”C#” %> <!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Transitional//EN” “http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd”> <script runat=”server”> [System.Web.Services.WebMethod] public static string GetQuote() { List<string> quotes = new List<string>(); quotes.Add(“The fool who is silent passes for wise.”); quotes.Add(“The early bird catches the worm.”); quotes.Add(“If wishes were true, shepherds would be kings.”); Random rnd = new Random(); return quotes[rnd.Next(quotes.Count)]; } </script> <html xmlns=”http://www.w3.org/1999/xhtml”> <head id=”Head1” runat=”server”> <title>Show Web Service Method</title> <script type=”text/javascript” src=”./Scripts/jquery-1.4.1.js”></script> <script type=”text/javascript”> $(document).ready(function () { $(“#btnGet”).click(function () { $.ajax({ type: “POST”, dataType: “json”, contentType: “application/json”, url: “ShowPageMethod.aspx/GetQuote”, success: function (data) { $(“#spanQuote”).html(data.d); }, error: function () { alert(“The call to the web service failed.”); } From the Library of Wow! eBook ptg 1781 Summary 40 }) }); }); </script> </head> <body> <form id=”form1” runat=”server”> <div> <input id=”btnGet” type=”button” value=”Get Quote” /> <br /><br /> <span id=”spanQuote”></span> </div> </form> </body> </html> Just like in the previous section, you can call a page method in the exact same manner as a web service. We pass in the URL and method name of our GetQuote() method to the $.ajax call, and our success and error references do the rest. This is handy when you develop page-specific functionality that doesn’t require the extra work of building a sepa- rate web service. Summary In the first part of this chapter, you learned about the jQuery library and what it has to offer. You learned about the $(document).ready() event and how to select elements with the $() jQuery function. In the next part, you learned how to call web services from the browser. You learned how to call a web method in an external web service and a static web method exposed from a server-side page. jQuery is a powerful tool that makes it incredibly easy to add client-based functionality to your web applications with little code. We have barely scratched the surface of what jQuery can do—it is a great way to improve the user experience of your applications, so spend some time to learn everything it has to offer. From the Library of Wow! eBook ptg This page intentionally left blank From the Library of Wow! eBook ptg Index Symbols $.ajax call, 1779 @Director parameter, 512 $(document).ready( ) method, jQuery, 1773-1774 / (forward slash), 1124 $get( ) method, 1754 @Id parameter, 512 $( ) method, jQuery, 1773-1774 %@ OutputCache % directive, 1337, 1369 CacheProfile attribute, 1361 Location attribute, 1349, 1351 VaryByControl attribute, 1342, 1344 VaryByCustom attribute, 1346-1349 VaryByHeader attribute, 1345-1346 VaryByParam attribute, 1338, 1342 ~ (tilde character), 1124 @Title parameter, 512 _ (underscore character), 730 A a templates, PagerTemplate, 509 Abandon( ) method, 1284-1285 About.asax file, 1092-1093 absolute cache expiration policy, 1376-1377 absolute expiration policy, Data Caching, 1390-1392 absolute layouts, 288-290 Absolute.css file, 288-290 From the Library of Wow! eBook . attribute, 1 345 -1 346 VaryByParam attribute, 1338, 1 342 ~ (tilde character), 11 24 @Title parameter, 512 _ (underscore character), 730 A a templates, PagerTemplate, 509 Abandon( ) method, 12 8 4- 1285. jQuery, 177 3-1 7 74 %@ OutputCache % directive, 1337, 1369 CacheProfile attribute, 1361 Location attribute, 1 349 , 1351 VaryByControl attribute, 1 342 , 1 344 VaryByCustom attribute, 1 346 -1 349 VaryByHeader. type=”text/javascript” src=”./Scripts/jquery-1 .4. 1.js”></script> <script type=”text/javascript” src=”./Scripts/jqueryClick.js”></script> <html xmlns=”http://www.w3.org/1999/xhtml”>
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