.net pdf 417 Working with client components in VS .NET

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Working with client components
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The best thing for growing confidence in manipulating client components is creating a trivial component. All this component does is display a greet message on the screen and notify you each time a stage in its internal lifecycle is reached. Our goal is to show you how a component is created and how you can participate in its lifecycle. Look at the code shown in listing 8.1.
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Listing 8.1 Code for the trivial component
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Type.registerNamespace('Samples'); Samples.TrivialComponent = function() { Samples.TrivialComponent.initializeBase(this); } Samples.TrivialComponent.prototype = { initialize : function() { Samples.TrivialComponent.callBaseMethod(this, 'initialize'); alert("I've been initialized!"); }, dispose : function() { alert("I m being disposed!"); Samples.TrivialComponent.callBaseMethod(this, 'dispose'); }, greet : function() { alert("Hello, I'm your first component!"); } } Samples.TrivialComponent.registerClass('Samples.TrivialComponent', Sys.Component);
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Looking at the call to registerClass in the previous listing, you see that the trivial component is a client class that derives from Sys.Component. To participate in the lifecycle of a component, you need to override the initialize and dispose methods in the constructor s prototype object. Method overriding was explained in chapter 3, when we talked about inheritance in the Microsoft Ajax Library. In the example, you override both methods to display a message box using the JavaScript alert function.
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Don t forget to call the base implementations of the initialize and dispose methods using the callBaseMethod method, as in listing 8.1. They perform important processing steps during the initialization and disposing phases of the component s lifecycle. Calling the base implementations ensures that a component is properly initialized and disposed.
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The trivial component also defines a method called greet. This method displays a greeting message using the alert function. Its purpose is to demonstrate that you can declare methods in a component the same way as in a client class created with the Microsoft Ajax Library.
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Let s see what it takes to create an instance of the trivial component. In chapter 3, you learned that you can create custom JavaScript objects by using a function the constructor in conjunction with the new operator. Unlike with custom JavaScript objects, using the new operator isn t enough to properly instantiate a client component. It s your responsibility to initialize the new instance and host it in the Application object. For this purpose, you must rely on a special method called $create, which is provided by the Microsoft Ajax Library. Listing 8.2 shows how that is done.
Listing 8.2 Code for testing the trivial component
Sys.Application.add_init(pageInit); function pageInit() { $create(Samples.TrivialComponent, {'id':'trivialComponent'}); } function pageLoad() { var trivialComponent = $find('trivialComponent'); trivialComponent.greet(); }
This listing introduces the methods you ll most often use when dealing with client components. These methods create an instance of a client component and access it when needed. $create is an alias or shortcut for the Sys.Component.create method. The advantage of this method is that it performs all the tasks related to the component-creation process. We ll look under the hood of the creation process in the next section; but note that $create is called in the init stage of the client page lifecycle. As you may recall from our discussion of the client component model, the init stage is the point at which client components are instantiated. The other method introduced in listing 8.2 is $find. This method, an alias for the Sys.Application.findComponent method, accesses a child component of the Application object. This is possible because Sys.Application becomes the container of all the client components instantiated using $create. If you pass the ID of a component to $find, you get back the corresponding instance. We ll talk more about IDs and the $find method in section 8.2.2. In the meantime, look at figure 8.5 to see the component in action.
Working with client components
Figure 8.5 The trivial component greets you.
Before we discuss in detail how client components are instantiated, let s review the aliases you ll use in the code that follows. Table 8.1 lists them along with the full method names and the tasks they accomplish.
Table 8.1 Shortcut Some of the aliases defined by the Microsoft Ajax Library Full method name What it does Returns a reference to a DOM element Creates, configures, and initializes an instance of an ASP .NET AJAX client component Returns a reference to a component
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