Flex Building User Interface Components

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design user interface components in flex is just like any other language. This presentation provides some guidelines as to how such components should be design and implemented with performance in …

design user interface components in flex is just like any other language. This presentation provides some guidelines as to how such components should be design and implemented with performance in mind.

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  • good reference for any language ui design
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  • In my opinion, this presentation serves as a good starting point in building your custom flex components.
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  • Dude you have done a great job putting it together. If you don’t mind I would like to use it on my website http://rishikdhar.com. And if you have time, would you mind updating it to version 3.0 or higher, so all the version comptability stuff is taken care of.
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  • A common coding practice is to divide an application into functional units, or modules, where each module performs a discrete task. Dividing your application into modules provides you with many benefits, including the following:Ease of development Different developers or development groups can develop and debug modules independently of each other. Reusability You can reuse modules in different applications so that you do not have to duplicate your work.Maintainability By developing your application in discrete modules, you can isolate and debug errors faster than you could if you developed your application in a single file.
  • Ideally components are placed inside another component or container or document. They fire events and have properties for configuration. As we said earlier components may contain other subcomponents. A point I’m going to stress now and always. Its never recommended to have public methods for components you should always try to introduce events for listening to your component and modify data properties to configure your components. using events and properties allow you to integrate smoothly with the UI model of flex and not create performance issues.
  • Simple Components: are components that standardize the look and feel for another component by extending it.Composite Components: are components that group one or more components together to control their layout using on of flexlayout container(vBox,hBox,canvas,panel)Complex Components: are “complex” , they modify a container, control behaviour and the way it lays its data Nonvisual Components: such as formatters, validator,
  • Constructor is called when you instantiate your component.CreateChildren is for instantiating your subcomponents Commitproperties for reading all assign properties … this may be called more than once Measure doing all measurmentsUpdateDisplaylist layout and drawing
  • Keep in mind , overriding methods is always little bit better than handling events inside a component because IF used correctly they reduce the number rendering cycles
  • Binding calls the setter of the property
  • Recommnedations Check if the value actually changed Create a flag to notify the component that the property changed Invalidate the component so it reapplies the property.
  • 2. Differentiate events from internal methods3. Constructor stuff -> preinitialize createChildren stuff -> initializecommitproperties, measure, updateDisplayList ->render, creationComplete (causing rerendering )
  • Dynamic data driven properties components like those that you don’t need if certain properties are set. Flex calls it when the call to the addChild() ….. That is why it might be called more than once check next slide
  • Recommendation Check if a subcomponent is already instantiated because createChildren might be called more than when
  • invalidateProperties() for deferred calculation, child managementinvalidateSize() for changes to the measured size of a componentinvalidateDisplayList() for changes to the appearance of a component


  • 1. Building User Interface Components
    FLEX 2.01
  • 2. In this presentation
    Component lifecycle and optimization tips
    Generalizing components
    Designing component API
  • 3. Why create Components?
    Ease of development 
  • 4. What are Components?
    UI Component
    Data Properties
    Data Properties
    Data Properties
  • 5. MXML vs. AS Flex Components
    Some basic guidelines include the following:
    • Simple components, it is simpler and faster to create them in MXML.
    • 6. Composite components that contains other components & the Layout of those other components can be set using one of the Flex layout containers, use MXML.
    • 7. Complex components, such as to modifying the way a container lays out its children, use ActionScript.
    • 8. Visual component forinstance creating a subclass from UIComponent, use ActionScript.
    • 9. Nonvisual component, such as a formatter, validator, or effect, use ActionScript.
  • Component Lifecycle
    From birth to death, A Component goes through a defined set of steps:
    Garbage Collection
    Building your prototype is the process of implementing this lifecycle…
  • 10. Component Lifecycle in FLEX
    Implementing the lifecycle boils down to these methods:
    Custom events
  • 11. Construction
    MXML-able components must have zero arg constructors
    Call super()…or the compiler will do it for you.
    Good place to attach your own event handlers
    Try to avoid creating children here…for best performance
  • 12. Construction
    <local:RandomWalk />
    Varinstance:RandomWalk = newRandomWalk();
    public function RandomWalk()
  • 13. Configuration
    MXML assigns properties before sub-components are attached and initialized (avoids duplicate code execution).
    Your properties (get, set functions) need to expect that subcomponents haven’t been created yet.
    Avoid creating performance bottlenecks: make set functions defer work until validation.
  • 14. Configuration
    Properties invalidated?
  • 15. Configuration (pattern)

    instance.dataProvider = xmlDataSet;
    instance.width = 600;
    instance.height = 200;
    instance.labelText = “hello”;
    Or via binding
    … labelText=“{hello}” width=“600” … dataprovider=“{xmlDataSet}”
    private var _labelText:String;
    private var _labelTextDirty;
    public function set
    If (_labelText != value)
    _labelText= value;
    //BAD _label.text = _labelText;
    _labelTextDirty = true;
    invalidateProperties(); //invalidation
  • 16. Attachment
    • Most component initialization is deferred until it gets attached to a Parent
    • 17. Styles may not be initialized until its ancestors get rooted to the displayList()
    • 18. Parent.addChild(At) calls initialize() method to trigger next phase…you can call this explicitly if necessary
    addChild (ComponentInstance)
    Component initialization begins
  • 19. Startup
    Trigger preinitialize
    initialization Phase
    Validation Phase
  • 20. Startup
    Startup happens in multiple sub-phases:
    1. ‘preinitialize’ event is dispatched
    2. createChildren method is called, adds sub-components
    3. ‘initialize’ event is called – component is fully created
    4. First validation pass occurs
    5. ‘creationComplete’ event is fired – component is fully commited, measured, and updated.
  • 21. Startup
    Parent-> preinitialize
    Parent-> createChildren
    Child-> preinitialize
    Child-> createChildren
    grandChild-> preinitialize
    grandChild-> createChildren
    grandChild-> initialize
    Child-> initialize
    Child2-> preinitialize
    Child2-> createChildren
    Child2-> initialize
    Parent-> initialize
    Parent-> commitProperties
    Child-> commitProperties
    grandChild-> commitProperties
    grandChild-> measure
    Child-> measure
    Parent-> measure
    Parent-> updateDisplayList
    Child-> updateDisplayList
    grandChild-> updateDisplayList
    Parent-> render
    Child-> render
    grandChild-> render
    grandChild-> creationComplete
    Child-> creationComplete
    Parent-> creationComplete
  • 22. Initialization : createChildren()
    Creating children here streamlines startup performance
    Follow the same pattern MXML uses: create, configure, attach.
    Flex components give subclasses first-crack at defining subcomponents.
    Don’t forget to call super.createChildren();
    Defer creating dynamic and data-driven components to commitProperties();
  • 23. Initialization : createChildren
    protected varcommitButton:UIComponent;
    override protected function createChildren():void
    if (commitButton == null) //only create once—why ?
    commitButton = new Button();
    Button(commitButton).label = “OK”;
    commitButton.addEventListener(MouseEvent.CLICK, commitHandler);
  • 24. Invalidation
    Flex imposes a deferred validation model
    Aggregate changes, defer work until the last possible moment
    avoid creating performance traps for your consumers
    Three main invalidation functions:
  • 25. Invalidation
    Rules of Thumb:
    1. Change values immediately
    2. Dispatch events immediately
    3. Defer Side-effects and calculations to commitProperties()
    4. Defer rendering to updateDisplayList()
    5. Be suspicious of rules of Thumb 
  • 26. Validation : commitProperties
    Invoked by the framework immediately before measurement and layout
    Use it to calculate and commit the effects of changes to properties and underlying data
    Avoid extra work: Use flags to filter what work needs to be done
    Proper place to destroy and create dynamic subcomponents based on changes to properties or underlying data.
  • 27. Validation : commitProperties
    override protected function commitProperties():void
    if (_cme_datachanged)
    { _ cme_datachanged = false; //reset flag
    //data change effects applied here
  • 28. Validation : measure
    Invoked by the framework when a component’s invalidateSize() is called
    Components calculate their ‘natural’ size based on content and layout rules.
    Implicitly invoked when component children change size.
    Don’t count on it: Framework optimizes away unnecessary calls to measure.
    Quick Tip: start by explicitly sizing your component, and implement this later.
  • 29. Validation : updateDisplayList
    Invoked by the framework when a component’s invalidateDisplayList() is called
    The ‘right’ place to do all of your drawing and layout
  • 30. Interaction
    Properties: Talk to your component
    Events: Listen to your component
    Public methods: Only in very specific cases where you can not use properties or events to fulfill the need
  • 31. Interaction: Events
    Events consist of:
    Name: A unique (per target) name identifying the type of event
    Target: the object that dispatched the event
    Event: An Object containing additional information relevant to the event
    Handler: the function invoked when the event occurs.
  • 32. Interaction: Events
    1. Handling Events
    Registering, removing, capture, bubble
    2. Dispatching Events
    Flex’s event system is extensible – you can define the events you need to make your component useful. – more on this later
    Remember that events will bubble up from your sub-components. If you don’t want that to happen, you need to explicitly stop them from propagating.
  • 33. How the Flash Player Works?
  • 34. Other topics
    Generalizing Components
    Designing Components
  • 35. Generalizing Components
    Three important concepts for generalizing your component
  • 36. Generalizing Components
    Three important concepts for generalizing your component
    Use Properties to generalize the behavior and data
    Use Skinning and Styling to generalize the look
    Use Templating to generalize the content.
  • 37. Generalizing Component : Templating
    Instance properties
    Properties typed as UIComponent can be set in MXML like any other property.
    Reparenting allows you to embed passed values into your own display tree.
    Allows you to define complex components with configurable parts
    public function set thumbnailView(value:UIComponent)
    _thumbnailView = value;
  • 38. Generalizing Component : Templating
    2. Item Renderers (Factories)
    Factories are used to generate multiple child components
    Data driven components use them to generate renderers for the data
    Allows you to separate management of the data from displaying the data.
    Quick Tips:
    Type your item renderers as IFactory
    Use the IDataRenderer interface to pass your data to the instances
    If you have additional data to pass, define a custom interface and test to see if it is supported first.
  • 39. Generalizing Component : Binding
    Databinding is there to eliminate boilerplate data routing code
    <mx:Button enabled=“{randomWalk.selectedItem != null}” />
    Any property can be the destination of a binding, but the source needs special Support
    Good rule of thumb: If you think someone might want to bind to it…make it bindable.
  • 40. Generalizing Component: Binding
    Add [Bindable] to your class:
    [Bindable] public class RandomWalk extends UIComponent { …
    Makes all public varsbindable
    Convenience feature for value objects.
    Add [Bindable] to your property
    [Bindable] public varselectedItem:Object;
    [Bindable] public function get selectedItem():Object { …
    Wraps the variable or property in an autogenerated get/set
    Good for simple properties.
    Roll your own event based bindings:
    [Bindable(event=“selectedItemChange”)] public function get selectedItem():Object { …
    dispatchEvent(new Event(“selectedItemChange”));
    Works well for read only and derived properties
  • 41. Designing you API: base Class?
    What Base Class should you extend?
    Base class for all component and containers
    Gateway to key flex functionality: styles, Containers, invalidation, etc.
    Best choice for most components
    Container (and derivatives):
    Only use if your customers will think of your component as a container
    Allows developers to specify children in MXML (but there are other ways)
    Scrolling, clipping, and chrome management for free
    Other ‘Leaf’ Components
    Good for minor enhancements and guaranteeing type compatibility
    Major Functionality changes run the risk of ‘dangling properties’
    Consider using aggregation instead
  • 42. Designing your API: MXML schema
    Remember, Your API defines your MXML schema
    ClassName -> XML Tags Name
    Package -> XML Namespace
    Properties -> XML Attributes
    Complex Properties -> Child Tags
  • 43. Designing your API: Examples
    A Few Examples:
    Choose Properties over Methods
    Properties can be set from MXML
    Avoid write-once properties
    Anything that can be set in MXML can be bound to.
    Use value objects for complex and multi-valued properties
    MXML makes object graphs simple
    <DataGridColumncolumnName=“revenue” width=“30” dataField=“revYr” />
    <DataGridColumncolumnName=“profit” width=“30” dataField=“profYr” />
    Use different names for styles, events, and properties.
  • 44. THANKSQuestions ?