chandra shekhar

Over 6 years of experience in Software Development including Analysis, Design and Development of various applications in Flash and Flex environment. Currently, I am associated with one of the India's leading IT company specialized in providing eLearning services, Magic Software Pvt. Ltd (http://www.magicsw.com).
In spare time I blog at http://actionscript.org and at my own weblog brupp.com

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Now once you have access to the view all the public objects can be accessed by helper; this way you dis-tangle the code from design. A viewhelper can serve multiple related views. Say if the main view has a sub-view called “FeedreaderView.mxml” then this view can have its method defined in the “FeedreaderViewHelper.as” itself. So we will put all our design elements that we created in our “Feedreader” post earlier here with only change that its events are now handled in FeedreaderViewHelper.

<?xml version="1.0" encoding="utf-8"?>
<mx:VBox xmlns:mx="http://www.adobe.com/2006/mxml" width="100%" height="100%" >
<mx:Script>
<![CDATA[
import com.brupp.view.FeedreaderViewHelper;
import com.adobe.cairngorm.view.ViewLocator;

[Bindable]
private var _objViewHelper:FeedreaderViewHelper;

public function onCreationComplete():void
{
<strong>_objViewHelper = ViewLocator.getInstance().getViewHelper("viewHelper") as FeedreaderViewHelper;</strong>

}
]]>
</mx:Script>
...

<mx:DataGrid id="dgFeed" width="100%" height="100%"
itemClick="{_objViewHelper.onItemClick(event)}"
doubleClickEnabled="true"
itemDoubleClick="{<strong>_objViewHelper.onItemDoubleClick(event)</strong>}">

...
</mx:VBox>

Two important things (in bold) to note. Notice in the code above how the helper is accessed and how the event handling is passed to helper. So just to get started with Cairngorm you need a view and a viewHelper and voila you started digging into the framework slowly.

Summarizing ViewHelper (taken from Cairngorm API documentation) :
ViewHelper is used to isolate command classes from the implementation details of a view. Model-View-Controller (MVC) best practices specify that command classes should interact with the view using the model (see the ModelLocator class), but, in some instances, command classes may require to both interrogate and update the view directly. Prior to performing any business logic, the command class may require to fetch values that have been set on the view; following completion of any business logic, the final task may be for a command class to update the View (user interface) with any results returned, or perhaps to switch the View entirely (to a different screen).

By encapsulating all the logic necessary for interrogating and updating a particular View into a single helper class, we remove the need for the command classes to have any knowledge about the implementation of the View. The ViewHelper class decouples our presentation from the control of the application.

A ViewHelper belongs to a particular View in the application; when a ViewHelper is created, its id is used to register against a particular View component (such as a particular tab in a TabNavigator, or a particular screen in a ViewStack). The developer then uses the ViewLocator to locate the particular ViewHelper for interrogation or update of a particular View.

I’m sure a lot of above must have started making sense to you now except the “Command” stuff. Right? Keep hooked to my future posts. So going back to the feedreader example we now need an event to call the web-service to populate our grid. CairngormEvent, Command and FrontController conjunction serves the purpose and we will see how in the next post.

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