Adding Client Capabilities to Server Controls Using the ASP.NET AJAX Control Toolkit - Part 2/Page 3
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Adding Client Capabilities to Server Controls Using the ASP.NET AJAX Control Toolkit [con't]
Adding Animations to Your Extender Control
The ASP.NET AJAX Control Toolkit comes with a rich animation framework that provides support for creating cool visual effects on your pages. The animation framework consists of a set of JavaScript and .NET classes that enable you to build up animations of all types, including animations that run sequentially or in parallel, animations that fade the opacity of a control in and out, and animations that transition from one color to the next. The framework provides support for building these animations using the JavaScript API directly or using a declarative approach that consists of adding markup in the HTML editor. The following sections examine how to add animation functionality to extender controls.
Animations Using the JavaScript API
The ImageRotator extender we created earlier provided little in the area of effects as the images switched and resulted in very fast transition from one image to the next, which wouldn't catch a viewer's attention. In this section, we create a new version of the ImageRotator, called the AnimatedImageRotator, that fades in the image as it switches from one image to the next and provides this feature in addition to the existing functionality of the ImageRotator. As we cover how to add this new animation functionality, we gloss over the topics we have already covered, focusing only on implementing the animation pieces. To add this functionality to the AnimatedImageRotator, we need to register the animation scripts with the AnimatedImageRotatorExtender class and add logic to the behavior class to call the animation when the image changes.
Registering the Animation Scripts
To register the script files so that they are downloaded to the browser, we need to add the RequiredScript attribute to the AnimatedImageRotator Extender class, as shown in Listing 11.12. We use the RequiredScript attribute in this case to ensure that the animation.js, timer.js, and common.js script files associated with the AnimationScripts type are included with the scripts brought down to the browser for our control. This style of adding scripts associated with a type is a common practice in the toolkit and is clean way to include dependent scripts associated with a type.
Listing 11.12 AnimatedImageRotator Extender Class
Calling Animation APIs
The ASP.NET AJAX Control Toolkit contains a JavaScript API that you can use to provide animation support on the client. In the case of our Animated ImageRotator extender, we will use the FadeAnimation, which is part of the animation API, to provide a fade-in effect when the images on our image control change. The JavaScript code to implement this functionality will be contained in our behavior class and will integrate with the existing features of the ImageRotator.
The AnimatedImageRotator behavior class, shown in Listing 11.13, takes the ImageRotator behavior and adds a fade animation when the image changes, to fade the image into view. The constructor of the FadeAnimation takes the target of the animation, the duration of the animation, the number of steps per second, the effect, the minimum opacity, the maximum opacity, and whether to adjust for layout in Internet Explorer. In our case, the BannerImage image control will be the target of our animation, and the duration of our animation will be hard coded to 20% of the time the image is visible. To provide a clean animation, we will set the animation steps to 150, and combine that with a fade-in effect that will cause the image to transition in when the image changes. During this transition, we will start off with an opacity of 0, which will give us a full view of the image background, and then through the 150 steps work our way to a full view of the image with an opacity of 1. Table 11.1 lists some of the FadeAnimation properties and provides a little more information about what they do.
After we associate the animation to the element, starting, stopping, and pausing the animation is just a method call away, making it simple to manipulate the animation. In the AnimatedImageRotator, the load event of the image is used to trigger the animation to play because it will be fired each time our Sys.Timer calls the _rotateImage method. To do this, we associated the _onLoadImage event handler with the onLoad event of the image and called the play method on the animation inside the function. Now each time the load event occurs, the animation plays, transitioning the image into view. One of the side effects of working with an animation in a situation like this is a potential race condition if the duration was set too long. When working with transition-type animations like the FadAnimation, pay close attention to how you are using it to ensure the animation will work in all cases.
Listing 11.13 AnimatedImageRotator Behavior Class
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