Deprecated.
The ViewLocator is a singleton class, that is used to retreive ViewHelper classes that can manipulate (get/set/switch) the user interface of a Cairngorm RIA.
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 instance, command classes may require the assistance of ViewHelpers to get/set the user interface associated with the work they are designed to perform. ViewHelper classes contain methods that allow them to interrogate (get) individual elements of the view, such as the values of form fields, and to update the user interface, such as setting the data provider on DataGrids or Listcomponents. Additionally, a command may choose to toggle the user interface from one view to another - for instance, to take the user to a checkout screen.
The ViewLocator class is used to allow commands to instantly retrieve the appropriate ViewHelper. A command need only know the canonical name of a ViewHelper and the ViewLocator will return an instance of the appropriate ViewHelper class. In this way, command classes can manipulate the View irrespective of its implementation.
See also:
Static methods
staticgetInstance():ViewLocator
Singleton access to the ViewLocator is assured through the static getInstance() method, which is used to retrieve the only ViewLocator instance in a Cairngorm application.
Wherever there is a need to retreive the ViewLocator instance, it is achieved using the following code:
var viewLocator:ViewLocator = ViewLocator.getInstance();staticreleaseInstance():Void
Releases the current instance so that the next call to getInstance()
returns a new instance.
Constructor
new()
The ViewLocator constructor should only be created through the static singleton getInstance() method. ViewLocator maintains a hash map of ViewHelpers, keyed on viewName with a particular view as the value stored in the hash map.
Methods
getViewHelper(viewName:String):ViewHelper
Retrieves the ViewHelper instance that has previously been registered with viewName.
Parameters:
viewName | The name of the view for which we wish to retrieve a ViewHelper, eg "login" |
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Returns:
The ViewHelper instance that is required to manipulate the view registered with viewName
register(viewName:String, viewHelper:ViewHelper):Void
Registers a viewHelper under a canonical viewName.
In order that the application developer need not know the implementation of the view, a ViewHelper capable of manipulating a given view is registered under a simple canonical name.
For example, a LoginViewHelper may allow the manipulation of a Login window, that may start life as a PopUpWindow, but later be changed to a screen in a ViewStack. By registering the LoginViewHelper with the viewName "login", then any code that fetches the ViewHelper by it's name "login", and then calls methods on the ViewHelper, is completely insulated from any changes in the implementation of the view, and the implementation of the ViewHelper.
If a view is already registered with the canonical name, and Error is thrown.
Parameters:
viewName | A simple canonical name for the view that the ViewHelper will manipulate, eg "login" |
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viewHelper | An instance of a ViewHelper |
registrationExistsFor(viewName:String):Bool
Returns whether a view has been registered with a canonical name.
If two views are registered with the same canonical name, the second entry will overwrite the first. This method can be used to check whether a view has already been registered with a canonical name.
Parameters:
The | canonical name for the view that the ViewHelper will check, eg "login" |
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Returns:
A Boolean that indicates if a view is already registered with that view name
unregister(viewName:String):Void
Unregisters a viewHelper using its canonical name.
Parameters:
viewName | The canonical name for the view to be removed |
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