Flex Component Life-cycle

What is it? Sequence of steps that occur when you create a component object from a component class. As part of this process, Flex automatically calls component methods, dispatches events, and makes the component visible.

Component Life-cycle steps Creation Construction Configuration Attachment Initialization Life Invalidation Validation

Creation – Construction Purpose Create an instance of a component class Configure the object by setting its initial properties Examples In Actionscript: var b:Button = new Button(); b.label = test; b.addEventListener(MouseEvent.CLICK, onClick); In MXML

Creation – Configuration Purpose Set initial properties with setters Generic setter features Check to see if the value has changed Set a private instance of the value Set a boolean flag to indicate the property has changed Schedule component for invalidation (if necessary) Dispatch binding events (optional) Adobe does this in their component framework.

Creation – Configuration Check to see if the value has changed private var _label:String = ; private var _labelChanged:Boolean = false; public function set label (value:String):void { if (_label != value) { } }

Creation – Configuration Set a private instance of the new value private var _label:String = ; private var _labelChanged:Boolean = false; public function set label (value:String):void { if (_label != value) { _label = value; } }

Creation – Configuration Set a boolean flag to indicate the value change private var _label:String = ; private var _labelChanged:Boolean = false; public function set label (value:String):void { if (_label != value) { _label = value; _labelChanged = true; } }

Creation – Configuration Schedule component for invalidation (optional) private var _label:String = ; private var _labelChanged:Boolean = false; public function set label (value:String):void { if (_label != value) { _label = value; _labelChanged = true; invalidateProperties(); invalidateSize(); invalidateDisplayList(); } }

Creation – Configuration Dispatch binding events (optional) private var _label:String = ; private var _labelChanged:Boolean = false; public function set label (value:String):void { if (_label != value) { _label = value; _labelChanged = true; invalidateProperties(); invalidateSize(); invalidateDisplayList(); dispatchEvent(new Event(labelChanged)); } }

Creation – Configuration Dispatch binding events (optional) [Bindable(labelChanged)] public function get label ():String { return _label; }

Creation – Attachment Purpose Attach the component to the display list. Component life-cycle is stalled after configuration until attachment occurs In Actionscript: panel.addChild(button); In MXML: Don't need to do anything, the child is automatically added according to how it is nested.

Creation – Initialization Consists of 1 life-cycle phase and 3 events preinitialize event is dispatched on the component Component is in a very raw state. Its children have not yet been added (including internal children) Use this event in rare circumstances (set the properties on a parent before the children are created) createChildren() method is called by Flex on the component override this method from UIComponent Add child components that make up your custom component Construct component, set properties, add to display list

Creation – Initialization Consists of 1 life-cycle phase and 3 events initialize event is dispatched At this point, the component's children have been added and the component's initial properties are set, but it has not been sized, positioned, or processed for layout Use this event to perform additional processing before layout childAdd event is dispatched from parent If the parent is also being initialized, its initialize event is dispatched when all of its children are added.

Life – Invalidation Deferred Validation Flex uses a deferred validation for rendering components in their various states Central concept in the component life-cycle Use private variables and boolean flags to defer setting any render-related properties until the proper validation method is reached

Life – Invalidation Deferred Validation 3 methods that trigger validation methods invalidateProperties() --> commitProperties() Use this to set any of the component's properties invalidateSize() --> measure() Use this to change the component's default size invalidateDisplayList() --> updateDisplayList() Use this to change the component's size or position

Life – Validation Purpose Apply the changes deferred until validation 3 Phases occur in validation commitProperties() measure() updateDisplayList()

Life – Validation commitProperties() Purpose Commit any changes to component properties Synchronize changes to occur at the same time or ensure that they are set in a specific order When is it called? Immediately after the initialize event during component creation Whenever invalidateProperties() is called What is its phase order This method is called before measure() or updateDisplayList() This allows you to set property values that influence size or position

Life – Validation commitProperties() Example

Life – Validation measure() Purpose Calculate the component's preferred width and height and its preferred minimum width and height When is it called? After commitProperties() during initialization When the invalidateSize() method is called NOTE: measure() will never be called if the component is given an explicit width or height What is its phase order? After commitProperties() and before updateDisplayList()

Life – Validation measure() Caveats Only 4 properties should normally be set in measure() measuredHeight The default height of the component measuredWidth The default width of the component measuredMinHeight The default minimum height of the component measuredMinWidth The default minimum width of the component Use getExplicitOrMeasuredHeight() and getExplicitOrMeasuredWidth() to get child proportions.

Life – Validation measure() Example

Life – Validation updateDisplayList() Purpose To position and size children Allow use of the Drawing API to draw on the component When is it called? After measure() during the initialization process When invalidateDisplayList() is called What is it's order? After measure()

Life – Validation updateDisplayList() Caveats Position children using move(x, y), size them using setActualSize(width, height) instead of using the x, y, width, height properties Adobe recommends these methods because they work better with Container layouts. These methods are said to be quirky at times, so if they don't work for some reason just set the properties manually.

Life – Validation updateDisplayList() unscaledWidth, unscaledHeight Arguments for updateDisplayList() Indicate the width and height of the component as dictated by its parent. They do not take scaleX and scaleY properties into account, so you will have to calculate scaling manually if needs be. updateComplete event is dispatched by the component after its updateDisplayList() is executed Use this event for actions that must be performed each time a component's characteristics change, not just when it is created.

Life – Validation updateDisplayList() Example