c# thoughtworks qrcode Lesson 2: Creating Client Scripts with the Microsoft AJAX Library in Visual C#

Encoder QR Code ISO/IEC18004 in Visual C# Lesson 2: Creating Client Scripts with the Microsoft AJAX Library

Lesson 2: Creating Client Scripts with the Microsoft AJAX Library
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ChAPTER 9
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document.forms[0].ButtonCollapse.value = "Close"; } } </script> </asp:Content>
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When you run the code, the two areas defined by the <div> tags are shown along with the toggle button. Clicking this button executes the JavaScript on the client. Figure 9-4 shows an example of what the page looks like in the browser.
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FigURE 9-4 The JavaScript and HTML in the browser window.
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This is a basic example. This type of functionality is also provided by the AJAX Control Toolkit and Web Parts in ASP.NET.
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In this example, the JavaScript code is embedded directly in the page. If your JavaScript code is to be reused across multiple pages, you might want to externalize it into separate .js files. This allows both reuse and caching. The JavaScript files will be cached by browsers and thus the performance of your page will be improved. You provide this functionality by first creating the .js file and then placing your code inside it. You then reference the file inside a <script/> tag in the <head/> area of your page. The following code shows an example.
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<script type="text/javascript" src="SiteScripts.js"></script>
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The preceding example does not use many ASP.NET controls. Instead, it uses the standard HTML <Input/> tag to define a button. This tag s onClick event will simply execute a JavaScript method. However, for an ASP.NET Button control, the onClick attribute is used to declaratively
474 ChAPTER 9 Working with Client-Side Scripting, AJAX, and jQuery
connect an ASP.NET Button control to its server-side event. Therefore, to connect an ASP.NET Button control to a client-side JavaScript method, you can use the onClientClick attribute. In fact, you can set both the onClick and onClientClick attributes to respond to both a server-side and a client-side event for the same control. (Note that returning false from onClick negates the postback, but using onClientClick is preferred for client-side only event processing.) The following code shows an example of how you might replace the Input tag in the previous example with an ASP.NET Button control.
<asp:button id=" ButtonCollapse" runat="server" text="Close" onClientClick="Collapse();" />
It is also important to note that you can reference ASP.NET controls inside your client-side script. You reference them based on their rendering as HTML. Their IDs are set to the same ID you set in your code. The ASP.NET controls also have the ClientId property for changing the client ID from that of the server (which by default is set to match the server s ID).
Adding Script Dynamically to an ASP.NET Page
Sometimes you might need to generate your JavaScript and add it to your page at run time. This could be because your controls are created at run time or because information that is added to the page determines the JavaScript that should be defined for the page. In either case, you can use the ClientScriptManager class to register JavaScript dynamically. An instance of the ClientScriptManager class is exposed through the Page object s ClientScript property. You use this property to add JavaScript to the page at run time, to determine whether a script has already been registered, and for other related tasks. To add a script, you define it inside a string or point to its file. You then call the Page.ClientScript.RegisterClientScriptBlock method. This method takes a type (typically the instance of the page or control), a key that uniquely identifies the script (to help avoid collisions), the script itself, and a Boolean value indicating whether you need the registration to generate script tags. As an example, suppose you have a TextBox that allows the user to enter a password. Suppose you also want to give the user the ability to check the password s strength as it is typed. You might leave this feature turned off by default but allow users to turn it on. When they do so, you need to dynamically register a client script with the page from your code. The following code shows the markup for this example page.
<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" Runat="Server"> <div> Enter Password<br /> <asp:TextBox ID="TextBoxPassword" runat="server" Width="250"></asp:TextBox>   <span id="passwordStrength"></span> <br /> <asp:CheckBox ID="CheckBoxPassStrengthOn" runat="server" Text="Turn on password strength checking" AutoPostBack="true" oncheckedchanged="CheckBoxPassStrengthOn_CheckedChanged" /> </div> </asp:Content>
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