what is flex

8/7/2019 What is Flex

1/12

What is Flex?

Flex is a convoluted term for sure. As the history of the product has evolved ithas been a j2ee server, an as framework, a compiler and and IDE among other

things.

In todays day and age we are at a released version 3, with version 4 in beta.The term flex typically refers to a way of developing flash platform applicationusing the components in the open source framework developed by adobe.

Flex applications are written as a combination of xml markup (mxml) andactionscript much in the same vein that html applications are written with JS.The big difference is that the output of all your mxml and actionscript files is asingle swf that can be embedded in a web page and displayed to the world. Youcan also use Flex to develop AIR applications, applications that can be installed

on a users desktop.

Although Adobe produces an IDE to help in developing Flex applications it is nota requirement.

Taking Things Further: ActionScript 3.0

While MXML defines the structure of your Flex application, ActionScript3.0 defines your application's behaviour.

Now, you may be thinking, "Hang on. If I can do so much with MXML,why do I need ActionScript 3.0?" Well here's the confusing part; MXMLis actually a pretty form of ActionScript 3.0. In fact, MXML is convertedto ActionScript 3.0 when you compile it. Let's look at an example thatshows how similar MXML and ActionScript 3.0 are. The following codecreates the same component (a Button), first in MXML, and then inActionScript 3.0:

layout="absolute" creationComplete="init()">

The application that results when you compile this file will look likethis:

You still need to use ActionScript in your application, however; you'llneed to define what happens when that button is clicked, for example.Look at it in this way: you design your application with MXML, and youmake it work with ActionScript 3.0. By using MXML and ActionScript,you're separating the structural code from the programming logic. This


2/12

is an important philosophy to remember when building Flexapplications -- especially when you're building complex componentsdown the track.

ActionScript 3.0 is an ECMAScript-based scripting language, which

means that it adopts the ECMA scripting language standards.ActionScript 3.0 is a giant leap forward from is predecessor,ActionScript 2.0. The reason for this is that ActionScript 3.0 is now atruly object oriented programming (OOP) language. In fact, the entireframework of Flex is made up of object classes that have been writtenby Adobe.

If you want to develop complex RIAs, I'd recommend that you investsome time in understanding OOP. Most of the programming done inFlex is event-driven, which means that functions are run when acomponent triggers an event (for example, when a mouse clicks abutton on the page). The Adobe Livedocs site has some greatexamples of object-oriented ActionScript.

The full details of ActionScript 3.0 syntax and OOP are beyond thescope of this article, but if you've done any JavaScript programmingbefore, you are certainly well on your way.
http://livedocs.adobe.com/flex/http://livedocs.adobe.com/flex/


3/12

Flex interview Questions

Q 1. Types of BindingAns: Using the curly braces ({}) syntaxUsing ActionScript expressions in curly bracesUsing the tag in MXMLUsing bindings in ActionScript(BindingUtils)

Q 2. How to create your own eventAns: Creating a subclass from the Event classUsing the Event metadata tagDispatching an event

Q 3. Event BubblingAns: The mechanism through which event objects are passed from the objects thatgenerates an event up through the containership hierarchy

Q 4. Life cycle of Flex Application/Component?Ans: Preinitialize: The application has been instantiated but has not yet createdany child components.Initialize: The application has created child components but has not yet laid outthose components.creationComplete: The application has been completely instantiated and has laidout all components

Q 5. How you implement MVC in your ApplicationAns: Cairngorm is based on the MVC model. It is specifically designed to facilitatecomplex state and data synchronization between the client and the server, whilekeeping the programming of the View layer detached from the data implementation.The role of the View layer in a Cairngorm application is to throw events and bind todata stored in the Model. Components on the View can bind to Value Objects or otherproperties in the Model (data) layer.In a Cairngorm Model, related data are stored in Value Objects (VOs), while simplevariables can be stored as direct properties of the ModelLocator class. A staticreference to the ModelLocator singleton instance is used by the View layers to locatethe required data.The Controller is the most sophisticated part of the Cairngorm architecture. TheController layer is implemented as a singleton FrontController. The FrontControllerinstance, which receives every View-generated event, dispatches the events to theassigned Command class based on the event's declared type.The Command class then processes the event by running the Command class'

execute() method, which is an ICommand interface method. The event object mayinclude additional data if required by the developer. The execute() method canupdate the central Model, as well as invoke a Service class which typically involvescommunication with a remote server. The IResponder interface, which is alsoimplemented by the Command class, includes onResult and onFault methods tohandle responses returned from the invoked remote service.

Q 6. Difference btw Java and Flex Getters SettersAns: When it comes to getters and setters, Java and AS are quite different, in that


4/12

getters and setters are part of the core ECMAScript language, whereas in Java,getters and setters are done through a naming convention.In Java, it is almost never a good idea to make member variables public. If you dodecide to make member variables public and then later want to change the interfaceto use getter/setter functions, you will have to modify all callers of your interfaces,which is onerous at best and in many cases, not possible (expecially when you are

creating code that is used by other people).Meanwhile, in ECMAScript, the externally visible interface doesnt change when I gofrom a member variable to a getter/setter and back again. In some sense, theinterface hiding is already accomplished in the language. Creating public membervariables is safe in this sense.Perhaps this is already obvious to all the AS-heads out there, but it took me a bit of time to get used to the concept.

Q 7. How many events are fired when your focus goes in one text box, you entersome text and then press tab.Ans: PreinitializeHandler(), initializeHandler(), itemEditBegin, itemEditEnd,creationComplete()

Q 8. How you use styles different ways of using Style sheetAns: Using external style sheets, Using local style definitions, Using theStyleManager class ,Using the setStyle() and getStyle() methods, Using inlinestylesLoading style sheets at run time

Q 9. How can you use two Styles at the same timeAns: Using external style sheets and use Inline style commands

Q 10. Try to remember properties of few imp componentsAns:< id="WeatherService" wsdl="http:/example.com/ws/WeatherService?wsdl"useproxy="false">

< !-- Bind the value of the ZIP code entered in the TextInput control to the ZipCodeparameter of the GetWeather operation. -->< name="GetWeather">

{zip.text}< /mx:request>< /mx:operation>

Q 11. What is the difference between Flex 2.0 and Flex 3.0Ans: Enhanced Features like Faster compilation time, SWF file size reduction,Flex/Ajax bridge, Advanced Datagrid, Interactive debugging, Cross-Domain,Versionable, Easy to Use,Security and Code Signing,Failover and Hosting,Cross-Domain RSL, Advanced DatagridDeep Linking, Resource Bundles and RuntimeLocalization, Flex Component Kit for Flash CS3, Compilation, LanguageIntelligenceRefactoring, Class Outline,Code Search, Profiler, Module Support, MultipleSDK Support, Skin Importer, Design View Zoom/Pan,Design Mode support forItemRenderers, Advanced Constraints, CS3 Suite integration, CSS Outline, CSSDesign View, Flex 3 SDK Skinning/Style Enhancements

Q 12. How will you call Java method from Flex?Ans: Using RemoteObject. Explain the process to interviewer


5/12

Q 13. What are the config files used for connecting Java and Flex?Ans:data-management-config.xml,messaging-config.xml,proxy-config.xml,

remoting-config.xml,services-config.xml

Q 14. What are the channels and their typesAns: The Channel class is the base message channel class that all channels in themessaging system must extend.Channels are specific protocol-based conduits for messages sent betweenMessageAgents and remote destinations. Preconfigured channels are obtained withinthe framework using the ServerConfig.getChannel() method. You can create aChannel directly using the new operator and add it to a ChannelSet directlyIn Flex AMFChannel is used mostly. Action Message FormatMethodsapplySettings (),connect(),connectFailed(),connectSuccess(),connectTimeoutHandler()disconnect(),disconnectFailed(),disconnectSuccess(),flexClientWaitHandler(),getMessageResponder(),internalConnect(),internalDisconnect(),internalSend(),logout()send(),setCredentials()Propertiesauthenticated,channelSets,connected,connectTimeout,endpoint,failoverURIs,protocol,reconnecting,recordMessageSizes,recordMessageTimes,requestTimeout,uri

Q 15. Give the name of Collection which can be mapped to java and Flex and vice-versaAns: java.lang.String String

java.lang.Boolean, boolean Boolean java.lang.Integer, int int java.lang.Short, short int java.lang.Byte, byte[] int java.lang.Byte[] flash.utils.ByteArray java.lang.Double, double Number java.lang.Long, long Number java.lang.Float, float Number java.lang.Character, char String java.lang.Character[], char[] String java. math.BigInteger String java.math.BigDecimal String java.util.Calendar Date java.util.Date Date java.util.Collection mx.collections.ArrayCollection(for example, java.util.ArrayList)java.lang.Object[] Arrayjava.util.Map Object (untyped). Forexample, a java.util.Map[] is converted to an array (of objects).

java.util.Dictionary Object (untyped)org.w3c.dom.Document XML object

java.lang.Object (other than previously listed types) Typed ObjectObjects are serialized by using JavaBean introspection rules and also include publicfields. Fields that are static, transient, or nonpublic, as well as bean properties that


6/12

are nonpublic or static, are excluded.

Q 16. How can you call JavaScript from MXMLAns: IExternalInterface.call()

Q 17. How can you access a var defined in 1 MXML flex in to another MXML file

Ans: Create 1 object of MXML fiel into another MXML File

Q 18 . Is it possible to make httpService Requests synchronous?Ans var mytoken:AsyncToken = yourservice.send();mytoken.addResponder(new ItemResponder(function,errorFunction));ORYou can create a result handler to your HTTPService.remoteObjectName.Your methodname.addEventListener("result",HandlerFunction,false,0,true);

Q 19 . I need to load an image from flickr into my application. Do I need acrossdomain.xml file on flickr?Ans: every SWF file you view runs locally on your machine. This means that a SWFwould have HTTP access to all machines behind the company firewall. To preventthis, every server other than the one the SWF is loaded from, needs to have acrossdomain.xml file in its root, listing all domains that have access to that particularserver

Q 20. What is the difference between httpService and Data Service?Basically, Flex allows three types of RPC services: HttpService, WebServices, andRemoteObject Services. In Flex, using the RemoteObjects specifies named orunnamed sources and connects to an Action Message Format (AMF) gateway,whereas using the HTTPService and WebService use named services or raw URLsand connect to an HTTP proxy using text-based query parameters or XML.Specifically, HTTPServices use raw HTTP requests, WebServices use the SOAP

protocol and RemoteObjects uses AMF3.

Q 21. How do you generate random numbers within a given limit with actionscript?Ans: var randNum:Number = Math.random()*100;

Q 22. Have you built any components with actionscript? If so explain how you did it?Ans:package myComponents{import mx.controls.Button;public class MyButton extends Button {public function MyButton() {super();label="Submit";}}}

Q 23. How do you implement push on a flex applications?AnsMessaging systems let separate applications communicate asynchronously as peersby passing packets of data called messages back and forth through a MessageService. A message usually consists of a header and a body. The header contains anidentifier and routing information. The body contains application data.


7/12

So, you will be building an application that allows you to asynchronously send datathrough the DS message service to our Flex client application. Here are some key DSmessaging terms:

Producer: Producers are applications that create/send messages to the destination.Consumer: Consumers are applications that receive messages from the destination.

Message Destination: Destinations are the resources used for both publish-subscribeand point-to-point messaging.Message Channel: The channel is the method for connecting producers andconsumers to the destination (using an endpoint).Message Endpoint: An endpoint is the interface responsible for encoding anddecoding data into messages.Message Adaptor: The adaptor defines the messaging implementation. Optionsinclude using the ActionScriptAdapter provided with DS, or an external Java MessageService (JMS) provider.

Q 24. I am going to add images into a tag. How will it resize itself?

Q 25. What is a resource Manager??

Q 26. What are the similarities between java and flex?

Q 27. What is the dynamic keyword used for?

Q 28. How do you implement push with flex data services?

Q 29. What are the methods called when a UI component is intialized?

Q 30. How do you implement drag and drop on components that do not supportondrag and ondrop?

Q 31. Can you write to the file system from flex?

Q 32. What is a drag manager?Ans: Manages the drag-and-drop operations; for example, its doDrag() methodstarts the drag operation.

Q 33. How do you call javascript from Flex?Ans: flash.external.ExternalInterface.call(function_name: String[, arg1, ...]):Object;

Q 34. How do you use a repeater?Ans:< id="rp" dataprovider="{dp}">< height="49" width="50" click="Alert.show(String(event.currentTarget.getRepeaterItem()) + ' pressed')" label="{String(rp.currentItem)}">< /mx:repeater>

Q 35. What are three ways to skin a component in flex?Ans: Graphical skins: Images that define the appearance of the skin. These imagescan JPEG, GIF, or PNG files, or they can be symbols embedded in SWF files. Typicallyyou use drawing software such as Adobe PhotoShop or Adobe Illustrator tocreate graphical skins.


8/12

Programmatic skins: ActionScript or MXML classes that define a skin. To changethe appearance of controls that use programmatic skins, you edit an ActionScript orMXML file. You can use a single class to define multiple skins.Stateful skins: A type of programmatic skin that uses view states, where each viewstate corresponds to a state of the component.The definition of the view statecontrols the look of the skin. Since you can have multiple view states in a

component, you can use a single component to define multiple skins.

Q 36 . How do you use css styles in flex?Ans: Using external style sheets, Using local style definitions, Using theStyleManager class ,Using the setStyle() and getStyle() methods, Using inlinestylesLoading style sheets at run time.

Q 37. What is the difference between sealed class and dynamic classes?Ans: Sealed Classes: ActionScript 3.0 introduces the concept of sealed classes. Asealed class possesses only the fixed set of properties and methods that weredefined at compile time; additional properties and methods cannot be added. Thisenables stricter compile-time checking, resulting in more robust programs. It alsoimproves memory usage by not requiring an internal hash table for each objectinstance. Dynamic classes are also possible using the dynamic keyword. All classes inActionScript 3.0 are sealed by default, but can be declared to be dynamic with thedynamic keyword.Dynamic classes A dynamic class defines an object that can be altered at run timeby adding or changing properties and methods. A class that is not dynamic, such asthe String class, is a sealed class. You cannot add properties or methods to a sealedclass at run time.dynamic class Protean{ //Use dynamic keyword before the name of class}

Q 38. What is e4X and XML?

Ans: E4X means "ECMAScript For XMLUsing E4X, we can develop code with XML data faster than was possible withprevious programming techniques. E4X provides a set of classes and functionality forworking with XML data. ActionScript 3.0 includes the following E4X classes: XML,XMLList, QName, and Namespace.Here is an example of manipulating data with E4X:var myXML:XML =< id="'1'">burger3.95< /item>< id="'2'">fries1.45< /item>< /order>trace (myXML.item[0].menuName); // Output: burgertrace (myXML.item.(@id==2).menuName); // Output: friestrace (myXML.item.(menuName=="burger").price); // Output: 3.95

Q 39. What is state? What is the difference between states and ViewStack?


9/12

Ans: View Stack is to handle different MXML file eg TAB control, and states is thetransition within single MXML file

Q 40. How does item renderer work? How do I add item renderer at runtime?

Q 41. . What keyword allows you to refer to private variables of a class?

Q 42. How polymorphism works on actionscript?

Q 43. . How do you overload functions in actionscript?

Q 44. What is dynamic keyword used for?Ans: Those Classes which should be extended and changed are called Dynamicclasses

Q 45. What are sealed classes?Ans: Classes whichyou cant extend. ex String

Q 46. What are runtime shared libraries?

Q 47. What is caringhorm? How do you use it? Have you worked with Cairngorms?

Q 48. What keyword allows you to implement abstraction better?

Q 49. What design patterns have you used? In Actionscript and java?

Q 50. What's the difference between Java and AS3 getters and setters? Ans: I haveto explicitly call a setter/getter function in Java, while AS3 allows me to Access mysetters and getters as though they are variables.Q 51. Explain the component lifecycle.Q 52. Tell me about dataServices

Q 53. understanding of MVCQ 54. They ask what frameworks you aree familiar with When getting developers tohelp create "standard" application, I'd weight a lot more heavily on the as3questions. Aside from basic "show me how you'd write X" algorithm questions, youcan ask more in depth ones about the workings of the language:Q 55. Explain how binding works in mxml components.

Q 56. Explain the ChangeWatcher.Wach()Ans: You can detect when a binding occurs in your application. Flex includes themx.binding.utils.ChangeWatcher class that you can use to define a watcher for adata binding. Typically, your event watcher invokes an event listener when thebinding occurs

Q 57. Why would you want to keep a reference to a ChangeWatcher and callunwatch()?Q 58. How do you add event listeners in mxml components. Now AS3 components?Q 59. What does calling preventDefault() on an event do? How is this enforced?Ans: Prevent defaults helps skipping the default behaviour or any componnent. Likein radio Button when you will click it will get selected, but if you want only the skin tobe changed you can use preventDefault()

Q 60. (If applicable) Explain the lifecycle of a Cairngorm action.
http://livedocs.macromedia.com/flex/2/langref/mx/binding/utils/ChangeWatcher.htmlhttp://livedocs.macromedia.com/flex/2/langref/mx/binding/utils/ChangeWatcher.html


10/12

Q 61. I was interviewed for a Flex position. The hiring manager kept on asking Javaand J2EE questions. So, I asked him politely: you are hiring me for a flex position,why do you keep on asking Java questions?Q 62. What are some ways to specify styles on components?

Q 63. What is the problem with calling setStyle()Ans: When you are instantiating an object and setting the styles for the first time,you should try to apply style sheets rather than use the setStyle() method because itis computationally expensive. This method should only be used when you arechanging an object's styles during run timeQ 64. Explain the difference between creating an effect and setting the target asopposed to adding an effectListenerQ 65. What do repeater components do?Q 66. How do you identify a component created in a repeater?

Q 67. What is state? What is the difference between states and ViewStack? Ans:View Stack is to handle different MXML file eg TAB control.And states is the transitionwithin single MXML file ViewStack should be used where there is complete change inthe controls used and States should be used when you just want to add or removeafew components based on certain conditions. Login/Registration/Forgot password isthe best example for using States as each page will either add or remove to thealready existing one.

Q 68. What is the difference between httpService and Data Service? Ans. The Flexpresentation layer communicates with the business layer by using Flex data services,which are objects you insert in a Flex file. Specifically, you can use Flex data servicesto interact with the following:* Web services* HTTP services* Remote objects

A Flex data service is an object you insert in an MXML file to communicate with thebusiness layer of a multi-tier application. You use data services to send and receivedata from web services, HTTP URLs, and remote objects such as server-based Javaobjects. An HTTP service is nothing more than an HTTP request to a URL. Theprimary purpose of HTTP services is to retrieve XML data from an external source.

Q 69. Why you dont Embed all images in your applicationAns: That increases the size of the SWF File

Q 70. What type of images can be loadedAns: (PNG, GIF, JPEG, SWF at run time and PNG, GIF, JPEG, SWF, SVG at compiletime)

Q 71. Explain ContainerCreationPolicyAns: This is used with the containers like Accordian, ViewStack etc. depending uponthe ContainerCreationPolicy you have set accordingly the child pages will be loaded.ALL Immediately create all descendants.AUTO: Delay creating some or all descendants until they are needed.NONE: Do not create any children.QUEUED: Add the container to a creation queue.

Q 72. What are the factory classes


11/12

Ans: Factory class The factory class creates an object of the instance class toperform the effect on the target. You create a factory class instance in yourapplication, and configure it with the necessary properties to control the effect, suchas the zoom size or effect duration.

Q 73. Explain Metadata

Ans: You insert metadata tags into your MXML and ActionScript files to provideinformation to the Adobe Flex compiler. Metadata tags do not get compiled intoexecutable code, but provide information to control how portions of your code getcompiled.

Q 74. I was asked too many questions on the event bubbling, Like how to captureand event if the component is disabled.Ans: addEventListner on the parents and enable the component in that handler

Q 75. obj.addEventListener(MouseEvent.CLICK, MouseClickHAndler); in this objshould inherit which class?Ans: DispachEventYou can manually dispatch events using a component instance's dispatchEvent()method. All components that extend UIComponent have this methodobjectInstance.dispatchEvent(event:Event):Boolean

Q 76. Why we extent Sprite Class in our Graphical Classes?

Q 77. What is Layout Manager and explain the Properties and Methods?Ans The LayoutManager is the engine behind Flex's measurement and layoutstrategy. Layout is performed in three phases; commit, measurement, and layout.The commit phase begins with a call to validateProperties(), which walks through alist (sorted by nesting level) of objects calling each object'svalidateProperties()method.

The objects in the list are processed by nesting order, with the most deeply nestedobject accessed first. This can also be referred to as bottom-up inside-out ordering.

The measurement phase begins with a call to validateSize(), which walks througha list (sorted by nesting level) of objects calling each object's validateSize() methodto determine if the object has changed in size.

The layout phase begins with a call to the validateDisplayList() method, whichwalks through a list (reverse sorted by nesting level) of objects calling each object'svalidateDisplayList() method to request the object to size and position allcomponents contained within it (i.e. its children).

Property of LayoutManagerusePhasedInstantiation : BooleanA flag that indicates whether the LayoutManager allows screen updates betweenphases.

Q 78. How do you call a method in particular ItemRenderer. Also the ItemRenderer isyour own Custom Component.Ans< id="comboBox" dataprovider="{statesXMLList}" labelfield="@name"


12/12

itemrenderer="ComboBoxItemRenderer">< /mx:Application>View ComboBoxItemRenderer.mxml< ?xml version="1.0" encoding="utf-8"?>

< mx="http://www.adobe.com/2006/mxml" stylename="plain">

< text="{data.@name}" onclick="MyOwnMethodThatIWantToCall()">< /mx:VBox>

Q 79. How can you implement Singleton in Flex Application?Ans: If you are a Java Programmer dont be mistaken by saying create PrivateConstructor. We cant create private Constructor in Flex.

Q 80. Give similiarities btw Java and FlexAns: Both are object Oriented, Encapsulation, Inheritance, Abstraction andPolymorphism are implemeted in both of the technologies.* The package like imports* Availability of Classes in the scripting language* Capabilities Arrays & ArrayCollections* On the UI end, similarities to SWING

what is flex

Documents