Adobe Flex 3 Component Life Cycle
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Adobe Flex 3 Component Life Cycle

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An updated version of our Adobe Flex 3 Component Lifecycle talk. I gave this presentation at CFUnited Express in Denver on 4/6/2009. ...

An updated version of our Adobe Flex 3 Component Lifecycle talk. I gave this presentation at CFUnited Express in Denver on 4/6/2009.

Brad Umbaugh and I gave the original in Nov. 2008 at 360 Flex San Jose. Brad Umbaugh wrote half of these slides.

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  • Very neat. I like the presentation style and of course the content too.Way to go RJ.
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    Adobe Flex 3 Component Life Cycle Adobe Flex 3 Component Life Cycle Presentation Transcript

    • Adobe Flex 3 Component Lifecycle Presented by RJ Owen This presentation originally created by RJ Owen and Brad Umbaugh in 11/08.
    • Who are we? ‣ RJ Owen Senior Technical Architect @ EffectiveUI • • Adobe Community Expert in Flex
    • Who are you (hopefully)? ‣ Beginner to intermediate level developers ‣ Anyone who doesn’t currently understand the lifecycle ‣ Anyone who wants a good review of the basics
    • What’s this about, anyway? ‣ Flex component lifecycle (duh) ‣ Flex frame cycle (“elastic racetrack”) ‣ Deferment!
    • Flex ‣ What is Flex? A set of components • • MXML • The component lifecycle!
    • Flex Component Lifecycle ‣ What is it? The way the framework interacts with • every Flex component • A set of methods the framework calls to instantiate, control, and destroy components • Methods that make the most of the elastic racetrack
    • Elastic Racetrack: introduction image courtesy of Ted Patrick ‣ Flex component lifecycle is built on this frame model ‣ More on this later
    • A frame in AS3 image courtesy of Sean Christmann
    • Phases of the Lifecycle ‣ 3 Main Phases: ‣ BIRTH: construction, con guration, • attachment, initialization ‣ LIFE: • invalidation, validation, interaction ‣ DEATH: • detachment, garbage collection
    • Birth Congratulations: You’re about to have a component.
    • Construction Birth construction con guration attachment initialization Life Death
    • What is a constructor? ‣ A function called to instantiate (create in memory) a new instance of a class Birth construction con guration attachment initialization Life Death
    • How is a constructor invoked? Actionscript: var theLabel : Label = new Label(); MXML: <mx:Label id=quot;theLabelquot;/> Birth construction con guration attachment initialization Life Death
    • What does a constructor have access to? ‣ Properties on the class ‣ Methods on the class ‣ Children have not yet been created! Birth construction con guration attachment initialization Life Death
    • What does an ActionScript3 constructor look like? public function ComponentName() { super(); //blah blah blah } ‣ No required arguments (if it will be used in MXML); zero, or all optional ‣ Only one per class (no overloading!) ‣ No return type ‣ Must be public Birth construction con guration ‣ Calls super() to invoke superclass constructor; if attachment you don’t, the compiler will! initialization Life Death
    • What does an MXML constructor look like? ‣ No need to de ne one. In fact, if you try to put one in an <mx:Script> block, you’ll get an error. ‣ Why? Remember: MXML = Actionscript. A constructor is created by the compiler in the Actionscript generated from the MXML. ‣ Specify “-keep” in the Flex Builder Birth compiler arguments and look at the construction con guration generated code to verify this. attachment initialization Life Death
    • What should a constructor do? ‣ Not much. Since the component’s children have not yet been created, there’s not much that can be done. ‣ There are speci c methods (such as createChildren) that should be used for most of the things you’d be tempted to put in a constructor. ‣ A good place to add event listeners to the Birth object. construction con guration attachment initialization Life Death
    • Don’t create or attach children in the constructor ‣ It’s best to delay the cost of createChildren calls for added children until it’s necessary Birth construction con guration attachment initialization Life Death
    • Con guration Birth construction con guration attachment initialization Life Death
    • Con guration ‣ The process of assigning values to properties on objects ‣ In MXML, properties are assigned in this phase, before components are attached or initialized <local:SampleChild property1=quot;value!quot;/> Birth construction con guration attachment initialization Life Death
    • Hooray: Sample code! <mx:Application ...> ... <local:SampleChild property1=quot;value!quot;/> </mx:Application> Output: SampleChild constructor SampleChild.property1 setter Birth Adding child SampleChild4 construction con guration attachment initialization Life Death
    • Con guration and Containers ‣ Containers must not expect their children have to be instantiated when properties are set. <mx:Application ...> <local:SampleContainer property1=quot;value!quot;> <local:SampleChild property1=quot;value!quot;/> </local:SampleContainer> </mx:Application> SampleContainer constructor Birth SampleContainer.property1 setter construction SampleChild constructor con guration attachment SampleChild.property1 setter initialization Life Death
    • Con guration Optimization ‣ To avoid performance bottlenecks, make your setters fast and defer any real work until validation ‣ We’ll talk more about deferment in the validation / invalidation section Birth construction con guration attachment initialization Life Death
    • Attachment Birth construction con guration attachment initialization Life Death
    • What is attachment? ‣ Adding a component to the display list (addChild, addChildAt, MXML declaration) ‣ The component lifecycle is stalled after con guration until attachment occurs. Birth construction con guration attachment initialization Life Death
    • Consider this component: public class A extends UIComponent (It traces all of its methods.) { public function A() { trace( quot;CONSTRUCTORquot; ); super(); } override protected function createChildren() : void { trace( quot;CREATECHILDRENquot; ); super.createChildren(); } override protected function measure() : void { trace( quot;MEASUREquot; ); super.measure(); } override protected function updateDisplayList(width:Number, height:Number) : void { trace( quot;UPDATEDISPLAYLISTquot; ); super.updateDisplayList(width,height); } override protected function commitProperties():void { trace( quot;COMMITPROPERTIESquot; ); super.commitProperties(); }
    • And this application: <mx:Application ...> <mx:Script> <![CDATA[ override protected function createChildren() : void { super.createChildren(); var a : A = new A(); } ]]> </mx:Script> </mx:Application> Output: CONSTRUCTOR ‣ Without attachment, the rest of the lifecycle doesn’t happen.
    • But what about this application? <mx:Application ...> <mx:Script> <![CDATA[ override protected function createChildren() : void { super.createChildren(); var a : A = new A(); this.addChild( a ); } ]]> </mx:Script> Output: CONSTRUCTOR </mx:Application> CREATECHILDREN COMMITPROPERTIES MEASURE UPDATEDISPLAYLIST ‣ Moral of the story: don’t add components to the stage until you need them.
    • Initialization Birth construction con guration attachment initialization Life Death
    • Initialization ‣ 2 phases, 3 events: 1. ‘preInitialize’ dispatched Create 2. createChildren(); called 3. ‘initialize’ dispatched Validate 4. rst validation pass occurs 5. ‘creationComplete’ dispatched Birth construction con guration attachment initialization Life Death
    • createChildren() ‣ MXML uses the createChildren() method to add children to containers ‣ Override this method to add children using AS Follow MXML’s creation strategy: create, • con gure, attach override protected function createChildren():void { ... create textField = new UITextField(); textField.enabled = enabled; con gure textField.ignorePadding = true; textField.addEventListener(quot;textFieldStyleChangequot;, textField_textFieldStyleChangeHandler); ... ... attach addChild(DisplayObject(textField)); }
    • createChildren() cont. ‣ Defer creating dynamic and data-driven components until commitProperties() ‣ UIComponent.createChildren() is empty, but it’s good practice to always call super.createChildren() anyway Birth construction con guration attachment initialization Life Death
    • rst validation pass ‣ Invalidation is not part of initialization - only Validation ‣ Validation consists of 3 methods: • commitProperties() • measure() • updateDisplayList() ‣ more on these later Birth construction con guration attachment initialization Life Death
    • Life They grow up so fast.
    • Invalidation Birth Life invalidation validation interaction Death
    • Invalidation / Validation cycle ‣ Flex imposes deferred validation on the Flash API • goal: defer screen updates until all properties have been set ‣ 3 main method pairs to be aware of: • invalidateProperties() -> commitProperties() • invalidateSize() -> measure() • invalidateDisplayList() -> updateDisplayList()
    • Invalidation / Validation theory ‣ First, a little theory.
    • Deferment ‣ Deferment is the central concept to understand in the component Life-cycle ‣ Use private variables and boolean ags to defer setting any render-related properties until the proper validation method
    • Text-book example Bad: public function set text(value:String):void { myLabel.text = value; // Possible Error! during first config phase, // myLabel might not exist! } Good: private var _text:String = quot;quot;; override protected function public function set text(value:String):void { commitProperties():void{ { textSet = true; _text = value; if(textChanged){ myLabel.text = _text; textChanged = true; textChanged = false; } invalidateProperties(); invalidateSize(); super.commitProperties(); } invalidateDisplayList(); }
    • The Elastic Racetrack revisited image courtesy of Sean Christmann Invalidation occurs here
    • Invalidation methods ‣ invalidateProperties() Any property changes • ‣ invalidateSize() • Changes to width or height ‣ invalidateDisplayList() • Changes to child component size or position Birth Life invalidation validation interaction Death
    • Invalidation example 1 <mx:Application> <mx:Script> <![CDATA[ import mx.collections.ArrayCollection; [Bindable] public var arr : ArrayCollection = new ArrayCollection(); public function onClick() : void { var c : int = 0; while( c++ < 20 ) { arr.addItem( c ); } } ]]> </mx:Script> <mx:VBox> <mx:Button label=quot;Click me!quot; click=quot;onClick()quot;/> <test:BadList id=quot;theListquot; dataProvider=quot;{arr}quot;/> </mx:VBox> </mx:Application>
    • Invalidation example 2 public class BadList extends VBox { private var _dataProvider : ArrayCollection; public function set dataProvider( arr : ArrayCollection ) : void { this._dataProvider = arr; arr.addEventListener( CollectionEvent.COLLECTION_CHANGE, dataProviderChangeHandler ); } private function dataProviderChangeHandler( e : Event ) : void { this.removeAllChildren(); for each( var n : Number in this._dataProvider ) { var l : Label = new Label(); l.text = n.toString(); this.addChild( l ); } } public function BadList() {} } Result: dataProviderChangeHandler called 20 times
    • Invalidation example 3 public class GoodList extends VBox { private var _dataProvider : ArrayCollection; private var _dataProviderChanged : Boolean = false; public function set dataProvider( arr : ArrayCollection ) : void { this._dataProvider = arr; arr.addEventListener( CollectionEvent.COLLECTION_CHANGE, dataProviderChangeHandler ); this._dataProviderChanged = true; this.invalidateProperties(); } override protected function commitProperties():void { super.commitProperties(); if( this._dataProviderChanged ) { this.removeAllChildren(); for each( var n : Number in this._dataProvider ) { var l : Label = new Label(); l.text = n.toString(); Result: commitProperties this.addChild( l ); called only twice (once } during initialization) this._dataProviderChanged = false; } } private function dataProviderChangeHandler( e : Event ) : void { this._dataProviderChanged = true; this.invalidateProperties(); } public function GoodList() {} }
    • Validation Birth Life invalidation validation interaction Death
    • The Elastic Racetrack revisited Validation occurs here
    • Validation ‣ Apply the changes deferred during invalidation ‣ Update all visual aspects of the application in preparation for the render phase ‣ 3 methods: • commitProperties() • measure() Birth • updateDisplayList() Life invalidation validation interaction Death
    • commitProperties() ‣ Ely says: “Calculate and commit the effects of changes to properties and underlying data.” ‣ Invoked rst - immediately before measurement and layout Birth Life invalidation validation interaction Death
    • commitProperties() cont. ‣ ALL changes based on property and data events go here ‣ Even creating and destroying children, so long as they’re based on changes to properties or underlying data ‣ Example: any list based component with empty renderers on the screen Birth Life invalidation validation interaction Death
    • measure() ‣ Component calculates its preferred (“default”) and minimum proportions based on content, layout rules, constraints. ‣ Measure is called bottom up - lowest children rst ‣ Caused by “invalidateSize()” ‣ NEVER called for explicitly sized Birth components Life invalidation validation interaction Death
    • overriding measure() ‣ Used for dynamic layout containers (VBox, etc.) ‣ Use getExplicitOrMeasuredWidth() (or height) to get child proportions ‣ ALWAYS called during initialization ‣ Call super.measure() rst! ‣ Set measuredHeight, measuredWidth for the default values; measuredMinHeight Birth and measuredMinWidth for the minimum. Life invalidation validation interaction Death
    • measure() cont. ‣ Not reliable - Framework optimizes away any calls to measure it deems “unecessary” ‣ Ely says: “Start by explicitly sizing your component and implement this later.” Birth Life invalidation validation interaction Death
    • updateDisplayList() ‣ All drawing and layout code goes here, making this the core method for all container objects ‣ Caused by invalidateDisplayList(); ‣ Concerned with repositioning and resizing children ‣ updateDisplayList() is called top-down Birth Life invalidation validation interaction Death
    • Overriding updateDisplayList() ‣ Usually call super.updateDisplayList() rst • super() is optional - don’t call it if you’re overriding everything it does ‣ Size and lay out children using move(x,y) and setActualSize(w,h) if possible • I never have good luck with setActualSize() Birth Life invalidation validation interaction Death
    • Elastic Racetrack cont. ‣ User Actions Dispatch invalidation events • • Interact with any non-validation events from this frame (mouse movements, timers, etc.)
    • Elastic Racetrack Cont. ‣ Invalidate Action Process all validation calls • ‣ Render Action • Do the heavy lifting - actually draw on the screen
    • The Elastic Racetrack revisited Queued Invalidation Deferred Validation Render!
    • Interaction Birth Life invalidation validation interaction Death
    • How do objects know when something happens? ‣ Events: objects passed around when anything interesting goes on (clicks, moves, changes, timers...) ‣ If something happens to a component, it “ res” or “dispatches” the event ‣ If another component wants to know when something happens, it “listens” for events Birth ‣ Event-based architecture is loosely- Life invalidation coupled validation interaction Death
    • Bene ts of Loosely-Coupled Architectures ‣ Everything becomes more reusable ‣ Components don’t have to know anything about the components in which they’re used Birth Life invalidation validation interaction Death
    • Who can dispatch events? ‣ Subclasses of EventDispatcher EventDispatcher inherits directly from • Object ‣ Simply call dispatchEvent(event) to re off an event when something happens Birth Life invalidation validation interaction Death
    • How to tell events apart? ‣ Event class Different classes allow for customized • payloads ‣ “type” eld: a constant Birth Life invalidation validation interaction Death
    • Common Events ‣ Event.CHANGE ‣ MouseEvent.CLICK ‣ FlexEvent.CREATION_COMPLETE ‣ Event.RESIZE ‣ MouseEvent.ROLL_OUT Birth Life invalidation validation interaction Death
    • Handling Events ‣ <mx:Button id=”theButton” click=”callThisFunction(event)”/> ‣ theButton.addEventListener( MouseEvent .CLICK, callThisFunction ) Birth Life invalidation validation interaction Death
    • Event Propagation ‣ Three phases: Capturing, Targeting, Bubbling Application Application Capturing Bubbling Phase Phase Target Targeting Phase Birth Life invalidation validation interaction Death
    • Event Propagation ‣ Three phases: Capturing, Targeting, Bubbling <mx:Application initialize=quot;onInitialize()quot;> <mx:Script> <![CDATA[ public function onInitialize() : void { this.addEventListener( MouseEvent.CLICK, clickHandler, true ); this.addEventListener( MouseEvent.CLICK, clickHandler, false ); outer.addEventListener( MouseEvent.CLICK, clickHandler, true ); outer.addEventListener( MouseEvent.CLICK, clickHandler, false ); inner.addEventListener( MouseEvent.CLICK, clickHandler, true ); inner.addEventListener( MouseEvent.CLICK, clickHandler, false ); button.addEventListener( MouseEvent.CLICK, clickHandler, true ); button.addEventListener( MouseEvent.CLICK, clickHandler, false ); } public function clickHandler( e : Event ) : void { trace(quot;----------------------------------------------------------quot;); trace(quot;TARGET: quot; + e.target.id ); trace(quot;CURRENT TARGET: quot; + e.currentTarget.id ); trace(quot;PHASE: quot; + ( e.eventPhase == 1 ? quot;CAPTUREquot; : ( e.eventPhase == 2 ? quot;TARGETquot; : quot;BUBBLEquot; ) ) ); } ]]> </mx:Script> <mx:VBox> <mx:Panel id=quot;outerquot;> <mx:TitleWindow id=quot;innerquot;> <mx:Button id=quot;buttonquot;/> </mx:TitleWindow> Birth </mx:Panel> </mx:VBox> Life </mx:Application> invalidation ‣ validation interaction Death
    • Event Propagation ---------------------------------------------------------- TARGET: button CURRENT TARGET: eventTest PHASE: CAPTURE ---------------------------------------------------------- TARGET: button CURRENT TARGET: outer PHASE: CAPTURE ---------------------------------------------------------- TARGET: button CURRENT TARGET: inner PHASE: CAPTURE ---------------------------------------------------------- TARGET: button CURRENT TARGET: button PHASE: TARGET ---------------------------------------------------------- TARGET: button CURRENT TARGET: inner PHASE: BUBBLE ---------------------------------------------------------- TARGET: button CURRENT TARGET: outer PHASE: BUBBLE ---------------------------------------------------------- Birth TARGET: button CURRENT TARGET: eventTest Life PHASE: BUBBLE invalidation validation interaction Death
    • Stopping events from propagating ‣ stopPropagation() : Prevents processing of any event listeners in nodes subsequent to the current node in the event ow ‣ stopImmediatePropagation() : Prevents processing of any event listeners in the current node and any subsequent nodes in the event ow Birth Life invalidation validation interaction Death
    • target vs. currentTarget ‣ target: the object that dispatched the event (doesn’t change) ‣ currentTarget: the object who is currently being checked for speci c event listeners (changes) Birth Life invalidation validation interaction Death
    • Dispatching events from custom components ‣ MXML: <mx:Metadata> [Event(name=quot;atePizzaquot;, type=quot;flash.events.BradEventquot;)] </mx:Metadata> ‣ Actionscript: [Event(name=quot;atePizzaquot;, type=quot;flash.events.BradEventquot;)] public class MyComponent extends UIComponent { ... } Birth Life invalidation validation interaction Death
    • gutterShark: event manager ‣ guttershark is Aaron Smith’s “Actionscript 3 Productivity Library” ‣ Contains a lot of stuff commonly needed when developing Flash web sites ‣ Includes an EventManager that’s helpful Birth Life invalidation validation interaction Death
    • gutterShark: event manager <mx:Application initialize=quot;onInitialize()quot;> <mx:Script> <![CDATA[ import net.guttershark.events.EventManager; private var em : EventManager; public function onInitialize( e : Event = null ) : void { em = EventManager.gi(); em.handleEvents(theButton,this,quot;onButtonquot;); } public function onButtonClick() : void { theLabel.text = quot;CLICKquot;; } public function onButtonMouseOver() : void { theLabel.text = quot;MOUSE OVERquot;; } public function onButtonMouseOut() : void { theLabel.text = quot;MOUSE OUTquot;; } ]]> Birth </mx:Script> <mx:VBox> Life <mx:Button id=quot;theButtonquot; label=quot;Click Me!quot;/> invalidation <mx:Label id=quot;theLabelquot;/> </mx:VBox> validation </mx:Application> interaction Death
    • gutterShark: event manager ‣ Supports many different types of events and the addition of more ‣ Easy integration with Google Analytics, Atlas, Webtrends ‣ http://www.guttershark.net Birth Life invalidation validation interaction Death
    • Death All good things come to an end.
    • Detachment Birth Life Death detachment garbage collection
    • Detachment ‣ “Detachment” refers to the process of removing a child from the display list ‣ These children can be re-parented (brought back to life) or abandoned to die ‣ Abandoned components don’t get validation calls and aren’t drawn ‣ If an abandoned component has no more active references, it *should* be garbage- Birth collected Life Death detachment garbage collection
    • Detachment cont. ‣ Re-parenting isn’t cheap, but it’s cheaper than re-creating the same component twice ‣ Children do not need to be removed from their parent before being re-parented, but always should be ‣ Consider hiding rather than removing • set visible and includeInLayout to false Birth Life Death detachment garbage collection
    • Garbage Collection Birth Life Death detachment garbage collection
    • Garbage Collection ‣ The process by which memory is returned to the system ‣ Only objects with no remaining references to them will be gc’d • Set references to detached children to “null” to mark them for GC ‣ Consider using weak references on event listeners ‣ Talk to Grant Skinner about forcing GC Birth Life http://gskinner.com/blog/archives/2006/08/as3_resource_ma_2.html • Death detachment garbage collection
    • Conclusion ‣ Defer, Defer, DEFER! ‣ Use validation methods correctly ‣ Remember the elastic racetrack ‣ Always look on the bright side of detachment.
    • References ‣ Ely Green eld: “Building a Flex Component” • http://www.on ex.org/ACDS/ BuildingAFlexComponent.pdf ‣ Cha c Kazoun, Joey Lott: “Programming Flex 2” by O’Reilly • http://oreilly.com/catalog/9780596526894/ ‣ Colin Moock: “Essential Actionscript 3.0” by O’Reilly • http://oreilly.com/catalog/9780596526948/ index.html
    • Questions? RJ Owen rj.owen@effectiveui.com twitter: rjowen http://rjria.blogspot.com