Flex 4 Component Lifecycle

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The talk goes into the details of how the flash player works, why a component needs a lifecycle and the various stages of a components life.

Related Experimental code can be found at http://weblog.mrinalwadhwa.com/2009/06/21/flex-4-component-lifecycle/

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Flex 4 Component Lifecycle

  1. 1. A Flex 4 Component’s life cycle Mrinal Wadhwa http://www.mrinalwadhwa.com
  2. 2. What is a life cycle?
  3. 3. Why does a Flex component need a life cycle?
  4. 4. Flex applications run in the Flash Player
  5. 5. What Flex can do is a subset of what the Flash Player can do, not a superset.
  6. 6. so to understand flex components better, lets take a deeper look at how the flash player works ...
  7. 7. Frames
  8. 8. Frames everything is done in frames ...
  9. 9. Frame Rate the number of frames processed per second (fps)
  10. 10. Frame Rate you can suggest the player a frame rate you would like your swf to have ...
  11. 11. Frame Rate [SWF(width=”800”,height=”600”,frameRate=”60”)] OR stage.frameRate = 60; OR <s:Application frameRate=”60” ... >
  12. 12. Frame Rate lets look at some code to see what the player does with this suggestion ... view code
  13. 13. Frame Rate some observations from our experiment ....
  14. 14. Frame Rate the player tries its best to maintain the suggested frame rate, but there are no guarantees ...
  15. 15. Frame Rate the actual framerate achieved may be lower or higher than what we suggested ...
  16. 16. Frame Rate browsers can force a lower framerate on the flash player ...
  17. 17. Frame Rate In Firefox and Safari, frame rate falls to about 10 if the Tab running the swf is out of focus ...
  18. 18. Frame Rate In Safari if window is minimized, framerate falls to zero ..
  19. 19. now lets take a deeper look at what happens inside each frame ..
  20. 20. now lets take a deeper look at what happens inside each frame .. lets look at some more test code first .. view code
  21. 21. code execution rendering 1 frame the length of the track represents the time taken by this frame
  22. 22. what we saw in our experiment .. code execution rendering 1 frame the length of the track represents the time taken by this frame
  23. 23. what we saw in our experiment .. code execution rendering heavy code execution 1 frame 1 frame the length of the track represents the time taken by this frame
  24. 24. what we saw in our experiment .. code execution rendering heavy code execution heavy rendering 1 frame 1 frame 1 frame the length of the track represents the time taken by this frame
  25. 25. Ted Patrick called this ... code execution rendering heavy code execution heavy rendering 1 frame 1 frame 1 frame the length of the track represents the time taken by this frame
  26. 26. The Elastic Racetrack code execution rendering heavy code execution heavy rendering 1 frame 1 frame 1 frame the length of the track represents the time taken by this frame
  27. 27. Sean Christmann did some more research on this ...
  28. 28. The Marshal he proposed AVM2 is controlled by something he called the Marshal ..
  29. 29. The Marshal the marshal is responsible for carving out time slices ...
  30. 30. The Marshal the duration of a slice can vary based on your OS,browser etc. just for our discussion lets assume a slice is 20ms long ..
  31. 31. A Marshaled Slice
  32. 32. A Marshaled Slice but all these actions may not happen on each slice ...
  33. 33. A Marshaled Slice Flash Player’s Event.RENDER event is fired at this point
  34. 34. A Marshaled Slice invalidate action and render action only happen in the last slice of a frame ..
  35. 35. lets experiment with some more code ... view code
  36. 36. so from our experiment the marshal does seem to be carving out 20ms slices ...
  37. 37. with 20ms slices ...
  38. 38. with 20ms slices ... code execution
  39. 39. with 20ms slices ... render
  40. 40. with 20ms slices ...
  41. 41. with 20ms slices ... code execution
  42. 42. with 20ms slices ... render
  43. 43. with 20ms slices ...
  44. 44. the marshal pre calculates the number of slices ...
  45. 45. long running code execution or render segments can extend a given slice beyond 20ms this may or may not cause the the duration of the frame to increase ...
  46. 46. A swfs actual framerate won’t exceed the Marshals rate defined for the player instance ...
  47. 47. Code can be executed more often then the compiled framerate ... i.e in a single frame calculation can happen many times but rendering happens only once at the end
  48. 48. Code can be executed more often then the compiled framerate ... i.e in a single frame calculation can happen many times but rendering happens only once at the end This is very significant
  49. 49. now lets come back to our original question ...
  50. 50. Why does a Flex component need a life cycle?
  51. 51. Since code can execute more often than rendering .. you could potentially do calculations that have no effect ...
  52. 52. for example, lets say you change the width of a component ...
  53. 53. this will cause the component, its container (and its containers container, so on ...), its surrounding components etc. to recalculate size and positioning of themselves and all their children .. i.e a lot of calculation will happen.
  54. 54. now in the next code segment you change width of your component again .... all that calculation will happen again ... now since code segments can execute more times than render segments ...
  55. 55. your first set of calculations for change in width could potentially be useless ..
  56. 56. ... this is the main reason a component needs a life cycle performance
  57. 57. so what is the life cycle of a component ...
  58. 58. BIRTH
  59. 59. BIRTH LIFE
  60. 60. BIRTH LIFE DEATH
  61. 61. Construction Addition BIRTH Initialization LIFE DEATH
  62. 62. Construction Addition BIRTH Initialization Invalidation LIFE Validation Update DEATH
  63. 63. Construction Addition BIRTH Initialization Invalidation LIFE Validation Update Removal DEATH
  64. 64. lets setup some breakpoints and walk through some code as we look at each of these phases ..
  65. 65. Construction var b:MyButton = new MyButton(); • not much happens in this phase • thats good because Constructors are not JIT • the component is given a name in FlexSprite • event listeners are added
  66. 66. Addition this.addChild(b); • calls addingChild(), $addChild() and childAdded() • a lot happens in addingChild(), • child’s parent and document properties are set etc. • $addChild() is the flash player method that adds the component to the display list • childAdded() calls the initialize() method of the child if not initialized
  67. 67. Initialization initialize(); // called by the parent’s childAdded • fires FlexEvent.PREINITIALIZE when it starts • calls createChildren() .. where children of this component are created and added to itself • fires FlexEvent.INITIALIZED when it ends
  68. 68. Construction Addition BIRTH Initialization a component has been born ...
  69. 69. Construction Addition BIRTH Initialization LIFE
  70. 70. Construction Addition BIRTH Initialization Invalidation LIFE Validation Update
  71. 71. Invalidation LIFE Validation Update
  72. 72. Invalidation invalidateProperties invalidateSize invalidateDisplayList Event.RENDER LIFE Validation commitProperties measure layoutChrome(optional) updateDisplayList Update
  73. 73. Invalidation/Validation cycle (Life) this is how the framework defers calculations to the end of the frame, just before rendering ...
  74. 74. Invalidation/Validation cycle (Life) when a property changes... •its new value is stored in a temp variable, •a dirty flag is set, •and invalidate methods are called.
  75. 75. Invalidation/Validation cycle (Life) the LayoutManager keeps track of invalidated components
  76. 76. Invalidation/Validation cycle (Life) the invalidation methods tell the LayoutManager that a component is now in an invalid state
  77. 77. Invalidation/Validation cycle (Life) LayoutManger listens for Event.RENDER and calls corresponding validate methods when the render event occurs
  78. 78. Invalidation/Validation cycle (Life) invalidateProperties commitProperties invalidateSize measure invalidateDisplayList updateDisplayList
  79. 79. Invalidation/Validation cycle (Life) finally an UPDATE_COMPLETE event is dispatched
  80. 80. Construction Addition BIRTH Initialization Invalidation LIFE Validation Update
  81. 81. Construction Addition BIRTH Initialization Invalidation LIFE Validation Update DEATH
  82. 82. Construction Addition BIRTH Initialization Invalidation LIFE Validation Update Removal DEATH
  83. 83. Removal (death) this.removeChild(b); • $removeChild() is the flash player method that removes the component from the display list
  84. 84. All that we saw till now has been the same since Flex 2 and Flash Player 9 .. maybe even before that, I’m not sure
  85. 85. So what has changed in Flex 4?
  86. 86. not much ....
  87. 87. not much .... at least from a life cycle perspective ..
  88. 88. Flex 3 Component Model (Halo)
  89. 89. Flex 4 Component Model (Spark) Flex 3 Component Model (Halo)
  90. 90. Flex 4 Component Model (Spark) Flex 3 Component Model (Halo) Spark is built on top of Halo ....
  91. 91. Flex 4 Component Model (Spark) Flex 3 Component Model (Halo) SkinnableComponent extends UIComponent ...
  92. 92. SkinnableComponent lives the same life cycle ...
  93. 93. the Skin is a child to the component and lives its own life cycle ...
  94. 94. lets step through some more code ...
  95. 95. some observations ...
  96. 96. createChildren() of SkinnableComponent calls validateSkinState() which in turn calls attachSkin() ...
  97. 97. attachSkin() creates the skin and adds it as a child ... which in turn kicks off the life cycle of the skin
  98. 98. attachSkin() also calls findSkinParts() which looks though the children of the skin and populates our declared static part references
  99. 99. attachSkin() also calls findSkinParts() which looks though the children of the skin and populates our declared static part references findSkinParts() calls partAdded() for all the static parts it finds
  100. 100. attachSkin() also calls findSkinParts() which looks though the children of the skin and populates our declared static part references findSkinParts() calls partAdded() for all the static parts it finds also throws an exception if it does not find a required part
  101. 101. at a later time, when you create a dynamic part using createDynamicPartInstance() that method calls partAdded() as well
  102. 102. ?
  103. 103. Mrinal Wadhwa http://www.mrinalwadhwa.com http://twitter.com/mrinal

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