Cairngorm Microarchitecture

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Cairngorm Microarchitecture
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Pronunciation

• Cairngorm (kârn gôrm)
• n. yellowish-brown variety of quartz, especially
  found in Scottish Cairngorm mountain.

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What is it?

• Collection of classes/interfaces against which we
  can compile
• Elegant collaboration and partitioning of design
  responsibilities
• "microarchitecture" - Provide the skeleton or
  internal structure of moving parts, around which
  the flesh and muscle particular to a business
  domain can be layered
• A standard way of building a Flex app.

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Why use it?

• Multiple developers working on the project, and
  run the risk of them all solving the same problem
  in multiple different ways
• Unified approach to problems
• Inject complex functionality in a well understood
  manner
• Promote, enable and encourage reuse (business
  objects, business services, etc.)

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The Pieces of Cairngorm

• Model Locator Stores all of your applications
  Value Objects (data) and shared variables, in one
  place. Similar to an HTTP Session object, except
  that its stored client side in the Flex interface
  instead of server side within a middle tier
  application server.
• View One or more Flex components (button, panel,
  combo box, Tile, etc) bundled together as a named
  unit, bound to data in the Model Locator, and
  generating custom Cairngorm Events based on user
  interaction (clicks, rollovers, dragndrop.)
• Front Controller Receives Cairngorm Events and
  maps them to Cairngorm Commands.
• Command Handles business logic, calls Cairngorm
  Delegates and/or other Commands, and updates the
  Value Objects and variables stored in the Model
  Locator
• Delegate Created by a Command, they instantiate
  remote procedure calls (HTTP, Web Services, etc)
  and hand the results back to that Command.
• Service Defines the remote procedure calls
  (HTTP, Web Services, etc) to connect to remote
  data stores.

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Cairngorm 2 Microarchitecture
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Model

• All client state data
• Anything retrieved from server
• Implements ModelLocator Cairngorm interface
• The model locator in an application is a
  singleton that the application uses to store the
  client side model.
• Summary Model is a Singleton containing data.

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View

• User Interface
• .mxml files w/controls (text fields, combobox,
  datagrid, etc.)
• All data is pulled from model via a binding

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Controller

• Allows communication between tiers of application
  via
• Events
• extend class
• com.adobe.cairngorm.control.CairngormEvent
• Commands
• implement interfaces
• com.adobe.cairngorm.commands.ICommand
• com.adobe.cairngorm.business.IResponder
  (optional)
• Tie Events and Commands together in Controller
  class
• Conduit between user events and model changes

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Events

• Events classes usually just a
• Collection of properties
• Constructor with params to populate those
  properties
• Used to pass data between layers of an
  application

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Event - example

• package com.echoeleven.controller.event
• import com.adobe.cairngorm.control.CairngormEvent
  
• import com.echoeleven.controller.ApplicationContr
  oller
• public class LoginEvent extends CairngormEvent
• public var usernameString
• public var passwordString
• public function LoginEvent(usernameString,
  passwordString)
• super(ApplicationController.EVENT_LOGIN)
• this.username username
• this.password password

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Command

• Service to Worker command pattern
• Must implement the Cairngorm Command interface
• If receiving data from server (e.g.
  RemoteObject), should also implement Responder
  Interface
• Command class must implement execute() method
• execute() usually takes an event argument as a
  parameter

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Command - example

• package com.echoeleven.controller.command
• import com.echoeleven.model.ApplicationModel
• import com.echoeleven.controller.event.LoginDataC
  hangeEvent
• public class LoginDataChangeCommand implements
  Command
• public function execute(eventParamCairngormEven
  t)void
• var eventLoginDataChangeEvent eventParam as
  LoginDataChangeEvent
• var appDataApplicationModel
  ApplicationModel.getInstance()
• appData.username event.username
• appData.password event.password

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Controller

• Tie Event and Command classes together in
  Controller class constructor
• addCommand( ApplicationController.EVENT_LOGIN,
  LoginCommand )
• Controller listens for event
• When event is dispatched, commands execute()
  method called (by controller)
• Conduit between user events and model changes

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Controller Big Picture

• View event triggered (e.g. click event)
• Caught by private method in view (mxml file)
• View method creates instance of event (extending
  CairngormEvent)
• View method dispatches that event via
  CairngormEventDispatcher
• Controller catches CairngormEvent and executes
  associated Cairngorm Command
• private function btnClick( eventEvent )void
• var evtLoginEvent new LoginEvent(userName.text
  , password.text)
• CairngormEventDispatcher.getInstance().dispatchEv
  ent( evt )

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Example Flow

• Create LoginDataChangeEvent class
• Create LoginDataChangeCommand class
• Connect Event to Command in controller
• Catch the TextField.change event, and call local
  function dataChange()
• Create instance of LoginDataChangeEvent and
  dispatch it
• LoginDataChangeCommand.execute() automatically
  called
• execute() method modifies Model
• Change to model reflected in View through binding

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Service Locator

• Singleton
• Abstracts data communication layer
• Defines which protocol (http, SOAP, AMF, etc.)
  and which endpoint params (which service, which
  channel, etc.)

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Business Delegate

• Who should handle the results of a server
  operation?
• Avoids attaching result/error routines to data
  services (e.g. RemoteObject)
• Allows Command to call remote object method, and
  handle the result and fault methods
• Multiple instances may exist

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Business Delegate

• The Business Delegate typically fulfills its role
  in collaboration with the Service Locator it
  uses the Service Locator to locate and look up
  remote services, such as web services, remote
  Java objects, or HTTP services. Once located, the
  Business Delegate invokes these services on
  behalf of the class that has delegated
  responsibility to it for business logic
  invocation.

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References

• Cairngorm Docs
• Borrowed contents from Scott Talsmas slide