Diving Deep with the Flex Component Life Cycle
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The document discusses the Flex component lifecycle, which consists of three main phases: birth, life, and death. The birth phase includes construction, configuration, attachment, and initialization. The life phase involves invalidation, validation, and interaction. Invalidation triggers the validation phase, which consists of commitProperties(), measure(), and updateDisplayList() methods. These methods apply deferred changes, measure component sizes, and update displays. The validation phase prepares components for rendering before the next frame.
![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.](https://image.slidesharecdn.com/divingdeepwiththeflexcomponentlifecycle-100913115235-phpapp02/85/Diving-Deep-with-the-Flex-Component-Life-Cycle-26-320.jpg)
![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>
</mx:Application> Output: CONSTRUCTOR
CREATECHILDREN
COMMITPROPERTIES
MEASURE
UPDATEDISPLAYLIST
‣ Moral of the story: don’t add components to the
stage until you need them.](https://image.slidesharecdn.com/divingdeepwiththeflexcomponentlifecycle-100913115235-phpapp02/85/Diving-Deep-with-the-Flex-Component-Life-Cycle-27-320.jpg)
![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="Click me!" click="onClick()"/>
<test:BadList id="theList" dataProvider="{arr}"/>
</mx:VBox>
</mx:Application>](https://image.slidesharecdn.com/divingdeepwiththeflexcomponentlifecycle-100913115235-phpapp02/85/Diving-Deep-with-the-Flex-Component-Life-Cycle-40-320.jpg)
![Event Propagation
‣ Three phases: Capturing, Targeting, Bubbling
<mx:Application initialize="onInitialize()">
<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("----------------------------------------------------------");
trace("TARGET: " + e.target.id );
trace("CURRENT TARGET: " + e.currentTarget.id );
trace("PHASE: " + ( e.eventPhase == 1 ? "CAPTURE" : ( e.eventPhase == 2 ? "TARGET" : "BUBBLE" ) ) );
}
]]>
</mx:Script>
<mx:VBox>
<mx:Panel id="outer">
<mx:TitleWindow id="inner">
<mx:Button id="button"/>
</mx:TitleWindow>
Birth </mx:Panel>
</mx:VBox>
Life </mx:Application>
invalidation
‣
validation
interaction
Death](https://image.slidesharecdn.com/divingdeepwiththeflexcomponentlifecycle-100913115235-phpapp02/85/Diving-Deep-with-the-Flex-Component-Life-Cycle-64-320.jpg)
![Dispatching events from custom
components
‣ MXML:
<mx:Metadata>
[Event(name="atePizza", type="flash.events.JoshEvent")]
</mx:Metadata>
‣ Actionscript:
[Event(name="atePizza", type="flash.events.JoshEvent")]
public class MyComponent extends UIComponent
{
...
}
Birth
Life
invalidation
validation
interaction
Death](https://image.slidesharecdn.com/divingdeepwiththeflexcomponentlifecycle-100913115235-phpapp02/85/Diving-Deep-with-the-Flex-Component-Life-Cycle-68-320.jpg)
Diving Deep with the Flex Component Life Cycle
- 1. Diving Deep with the Flex Component Lifecycle Joshua Jamison EffectiveUI www.effectiveui.com January 30, 2009
- 2. Who am I? ‣ Joshua Jamison • Software Architect @ EffectiveUI
- 3. 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
- 4. What’s this about, anyway? ‣ Flex component lifecycle ‣ Flex frame cycle (“elastic racetrack”)
- 5. 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
- 6. Elastic Racetrack: introduction image courtesy of Ted Patrick ‣ Flex component lifecycle is built on this frame model ‣ More on this later
- 7. A frame in AS3 image courtesy of Sean Christmann
- 8. Phases of the Lifecycle ‣ 3 Main Phases: ‣ BIRTH: • construction, con guration, attachment, initialization ‣ LIFE: • invalidation, validation, interaction ‣ DEATH: • detachment, garbage collection
- 9. Birth Congratulations: You’re about to have a component.
- 10. Construction Birth construction con guration attachment initialization Life Death
- 11. 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
- 12. How is a constructor invoked? Actionscript: var theLabel : Label = new Label(); MXML: <mx:Label id="theLabel"/> Birth construction con guration attachment initialization Life Death
- 13. 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
- 14. 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 Birth ‣ Must be public construction con guration ‣ Calls super() to invoke superclass constructor; if attachment initialization you don’t, the compiler will! Life Death
- 15. 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. Birth ‣ Specify “-keep” in the Flex Builder construction con guration compiler arguments and look at the attachment generated code to verify this. initialization Life Death
- 16. 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. Birth ‣ A good place to add event listeners to the construction con guration object. attachment initialization Life Death
- 17. 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
- 18. Con guration Birth construction con guration attachment initialization Life Death
- 19. 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="value!"/> Birth construction con guration attachment initialization Life Death
- 20. Hooray: Sample code! <mx:Application ...> ... <local:SampleChild property1="value!"/> </mx:Application> Output: SampleChild constructor Birth SampleChild.property1 setter construction Adding child SampleChild4 con guration attachment initialization Life Death
- 21. Con guration and Containers ‣ Containers must not expect their children have to be instantiated when properties are set. <mx:Application ...> <local:SampleContainer property1="value!"> <local:SampleChild property1="value!"/> </local:SampleContainer> </mx:Application> SampleContainer constructor Birth construction SampleContainer.property1 setter con guration SampleChild constructor attachment SampleChild.property1 setter initialization Life Death
- 22. 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
- 23. Attachment Birth construction con guration attachment initialization Life Death
- 24. 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
- 25. Consider this component: public class A extends UIComponent { public function A() { (It traces all of its methods.) trace( "CONSTRUCTOR" ); super(); } override protected function createChildren() : void { trace( "CREATECHILDREN" ); super.createChildren(); } override protected function measure() : void { trace( "MEASURE" ); super.measure(); } override protected function updateDisplayList(width:Number, height:Number) : void { trace( "UPDATEDISPLAYLIST" ); super.updateDisplayList(width,height); } override protected function commitProperties():void { trace( "COMMITPROPERTIES" ); super.commitProperties(); }
- 26. 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.
- 27. 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> </mx:Application> Output: CONSTRUCTOR CREATECHILDREN COMMITPROPERTIES MEASURE UPDATEDISPLAYLIST ‣ Moral of the story: don’t add components to the stage until you need them.
- 28. Initialization Birth construction con guration attachment initialization Life Death
- 29. 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
- 30. 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("textFieldStyleChange", textField_textFieldStyleChangeHandler); ... ... attach } addChild(DisplayObject(textField));
- 31. 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
- 32. Life They grow up so fast.
- 33. Invalidation Birth Life invalidation validation interaction Death
- 34. 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()
- 35. Invalidation / Validation theory ‣ First, a little theory.
- 36. 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
- 37. 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 = ""; public function set text(value:String):void override protected function { commitProperties():void{ textSet = true; { _text = value; if(textChanged){ textChanged = true; myLabel.text = _text; textChanged = false; invalidateProperties(); } invalidateSize(); super.commitProperties(); invalidateDisplayList(); } }
- 38. The Elastic Racetrack revisited image courtesy of Sean Christmann Invalidation occurs here
- 39. 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
- 40. 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="Click me!" click="onClick()"/> <test:BadList id="theList" dataProvider="{arr}"/> </mx:VBox> </mx:Application>
- 41. 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
- 42. 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 } this._dataProviderChanged = false; during initialization) } } private function dataProviderChangeHandler( e : Event ) : void { this._dataProviderChanged = true; this.invalidateProperties(); } public function GoodList() {} }
- 43. Validation Birth Life invalidation validation interaction Death
- 44. The Elastic Racetrack revisited Validation occurs here
- 45. 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 Life • updateDisplayList() invalidation validation interaction Death
- 46. 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
- 47. 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
- 48. 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 Life components invalidation validation interaction Death
- 49. 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 Birth the default values; measuredMinHeight Life invalidation and measuredMinWidth for the minimum. validation interaction Death
- 50. measure() cont. ‣ Not reliable - Framework optimizes away any calls to measure it deems “unecessary” Birth Life invalidation validation interaction Death
- 51. 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
- 52. 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
- 53. Elastic Racetrack cont. ‣ User Actions • Dispatch invalidation events • Interact with any non-validation events from this frame (mouse movements, timers, etc.)
- 54. Elastic Racetrack Cont. ‣ Invalidate Action • Process all validation calls ‣ Render Action • Do the heavy lifting - actually draw on the screen
- 55. The Elastic Racetrack revisited Queued Invalidation Deferred Validation Render!
- 56. Interaction Birth Life invalidation validation interaction Death
- 57. 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 Life ‣ Event-based architecture is loosely- invalidation validation coupled interaction Death
- 58. 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
- 59. 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
- 60. How to tell events apart? ‣ Event class • Different classes allow for customized payloads ‣ “type” eld: a constant Birth Life invalidation validation interaction Death
- 61. Common Events ‣ Event.CHANGE ‣ MouseEvent.CLICK ‣ FlexEvent.CREATION_COMPLETE ‣ Event.RESIZE ‣ MouseEvent.ROLL_OUT Birth Life invalidation validation interaction Death
- 62. Handling Events ‣ <mx:Button id=”theButton” click=”callThisFunction(event)”/> ‣ theButton.addEventListener( MouseEvent .CLICK, callThisFunction ) Birth Life invalidation validation interaction Death
- 63. Event Propagation ‣ Three phases: Capturing, Targeting, Bubbling Application Application Capturing Bubbling Phase Phase Target Targeting Birth Phase Life invalidation validation interaction Death
- 64. Event Propagation ‣ Three phases: Capturing, Targeting, Bubbling <mx:Application initialize="onInitialize()"> <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("----------------------------------------------------------"); trace("TARGET: " + e.target.id ); trace("CURRENT TARGET: " + e.currentTarget.id ); trace("PHASE: " + ( e.eventPhase == 1 ? "CAPTURE" : ( e.eventPhase == 2 ? "TARGET" : "BUBBLE" ) ) ); } ]]> </mx:Script> <mx:VBox> <mx:Panel id="outer"> <mx:TitleWindow id="inner"> <mx:Button id="button"/> </mx:TitleWindow> Birth </mx:Panel> </mx:VBox> Life </mx:Application> invalidation ‣ validation interaction Death
- 65. 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
- 66. 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
- 67. 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
- 68. Dispatching events from custom components ‣ MXML: <mx:Metadata> [Event(name="atePizza", type="flash.events.JoshEvent")] </mx:Metadata> ‣ Actionscript: [Event(name="atePizza", type="flash.events.JoshEvent")] public class MyComponent extends UIComponent { ... } Birth Life invalidation validation interaction Death
- 69. Death All good things come to an end.
- 70. Detachment Birth Life Death detachment garbage collection
- 71. 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 Birth active references, it *should* be garbage- Life Death collected detachment garbage collection
- 72. 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
- 73. Garbage Collection Birth Life Death detachment garbage collection
- 74. 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 ‣ Talk to Grant Skinner about forcing GC Birth • http://gskinner.com/blog/archives/2006/08/as3_resource_ma_2.html Life Death detachment garbage collection
- 75. Conclusion ‣ Defer, Defer, DEFER! ‣ Use validation methods correctly ‣ Remember the elastic racetrack
- 76. 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