Any Which Array But Loose


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360|Flex Presentation on Arrays, Vectors, ByteArrays, Lists and Collections

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Any Which Array But Loose

  1. 1. Any Which Array But Loose Michael Labriola Digital Primates
  2. 2. Who are you? Michael Labriola Senior Consultant at Digital Primates Flex Geek Component Developer Flex Team Mentor
  3. 3. Who were you? Michael Labriola Software Engineer Embedded Systems Developer Reverse Engineer
  4. 4. What is this session about? This session is part of my continuing quest to teach Flash and Flex from the inside out. Learn what the Flash Player and the Flex framework are really doing and you are more likely to use them successfully, respect their boundaries and extend them in useful ways
  5. 5. One more reason Let’s call it “Game Theory”. If you know how something works really well, you know which rules you can bend and just how far you can bend them before they break. Sometimes you can even find really creative ways out of difficult situations
  6. 6. Standard Disclaimer I am going to lie to you a lot… a whole lot Even at this ridiculous level of detail, there is much more All of this is conditional. So, we are just going to take one route and go with it
  7. 7. What is an Array? Arrangement of objects in memory. Generally used to hold values in a directly index- able form
  8. 8. An Array Mostly contiguous block of memory Holds values Can grow or shrink in size at runtime
  9. 9. An Array Can Be Homogeneous Heterogeneous
  10. 10. An Array Can Be Dense Sparse
  11. 11. Null versus Sparse Array with Null Sparse
  12. 12. What is a Vector? A Vector is a new type of Array introduced with Flash Player 10. It’s primary benefits are performance and type safety
  13. 13. A Vector Is Dense (no gaps) Is Homogenous (always the same base class) Can be fixed length
  14. 14. Syntax Array Vector var a:Array = new Array(); var v:Vector.<uint> = new Vector.<uint>(n); a[0] = “value”; v[0] = “value”; //error a[1] = 345; v[1] = 345; a.push( 123 ); v.push( 123 ); trace( v.length ); trace( v.length );
  15. 15. A ByteArray About the lowest level memory access there is in ActionScript Let’s you access the raw bytes and order of data. Up to you to manage what exists inside of the array
  16. 16. Syntax ByteArray var byteArray:ByteArray = new ByteArray(); byteArray.writeBoolean(true); byteArray.writeDouble(Math.PI); byteArray.position = 0; trace( byteArray.readBoolean() ); //true trace( byteArray.readDouble() ); //3.1415926535897 trace( byteArray[ 2 ] ); //9… why?
  17. 17. Breaking Apart Pete When working with a ByteArray, the indices do not necessarily indicate discrete objects. They indicate discrete bytes
  18. 18. Position Byte Array also has a position indicator. This indicates the next place you will read from or write to. This is the beginning of a very important concept.
  19. 19. Great Things about Array Array’s can be extremely fast to access data at a known index. They also provide random access, meaning you can ask for the value at position 3 without caring that there is a position 2
  20. 20. Bad Things about Array Array’s can be pretty slow when you need to insert or delete information from the middle Moving from element to element (moving from 2 to 3) takes a fixed amount of time, which is good, but you also don’t get a speed advantage because those two are right next to eachother
  21. 21. Array Before Insert
  22. 22. Array Move Elements
  23. 23. Array Insert Element
  24. 24. Array Before Delete
  25. 25. Array Remove Element
  26. 26. Array Collapse
  27. 27. Array Searching Searching an Array generally involves iterating through each element looking for the value you would like. If the array is sorted, you can make the search a smarter
  28. 28. Array Collections At some point you may have been told to use the ArrayCollection class. So, what is it? ..It’s a wrapper around an array. It provides the basic access to array by acting as a proxy. This allows ArrayCollection to lie to you
  29. 29. Key Lies Since ArrayCollection controls all information flow in and out of its little regime, it can lie both about how big the array is and about the order of the elements. It does this by creating a duplicate array that points to the original, when and if it is convenient. Fortunately, you control this by means of the sort and filterFunction
  30. 30. Sorted Array Collection One you have provided the ArrayCollection a Sort instance and called its refresh() method, it builds an array which maps the original elements to the new sort
  31. 31. Syntax ArrayCollection Sort var ac:ArrayCollection = new ArrayCollection(data); var ac:ArrayCollection = new ArrayCollection(); var sort:Sort = new Sort(); var field:SortField = new SortField( quot;hireDatequot; ); sort.fields = [ field ]; ac.sort = sort; ac.refresh();
  32. 32. Collection Resorted Sorting doesn’t actually need to shift the original data, just the new internal array.
  33. 33. Searching a Collection Once an ArrayCollection has been sorted, searching it is a very efficient and easy process. The reduction in time to sort a large ArrayCollection is very significant over an array.
  34. 34. Filtered Array Collection One you have provided the ArrayCollection with a filter function and called its refresh() method, it builds an array which maps the original elements to the new array if they pass the test in your function
  35. 35. Syntax ArrayCollection Filter var ac:ArrayCollection = new ArrayCollection(); ac.filterFunction = ifIFeelLikeIt; ac.refresh(); function ifIFeelLikeIt( item:Object ):Boolean { //do some logic and decide return ( item != Andy ); }
  36. 36. Andy Filtered Out
  37. 37. Another Key Feature While not busy deceiving you, ArrayCollection has a handful of really useful additional features. The reason most people use ArrayCollection, even if they aren’t sure why, is that it is an event dispatcher. When you use the ArrayCollection with DataBinding, the ArrayCollection informs you of changes
  38. 38. Collection Broadcaster
  39. 39. Collection Internals trace( collection[ 3 ] ); getProperty( 3 ); getItemAt( 3 ); get localIndex[ 3 ]; setProperty( 3, 8 ); collection[ 3 ] = 8; setItemAt( 8, 3 ); list.setItemAt; Update Value Dispatch Event
  40. 40. Final One Through inheritance ArrayCollection also provides one final important feature, it can work with a cursor. A bit like the position in a ByteArray, the cursor points to a given object in the collection. You can use the cursor to move forward to the next item, move back to a previous item, seek to well-known locations or search sorted data.
  41. 41. Cursor
  42. 42. Cursor.moveNext()
  43. 43. DataGrid and List Base In fact, the List base controls in Flex use these cursors pretty much exclusively inside of these components. One of the reasons they can accept many different types of input is they simply wrap the input in one of (n) classes that implement ICollectionView
  44. 44. ICollectionView ICollectionView mandates that an object can dispatch events, understands how to sort, filter and refresh along with a handful of other items, and, most importantly, that the object can create a cursor that will move through an child objects.
  45. 45. ICollectionView This is really important as it allows us to use various types of Data Structures, other than just ArrayCollection to fill this need. For example, we can trivially make a VectorCollection which uses vectors instead of Arrays. We can create a ByteArrayCollection should we feel so inclined.
  46. 46. Cursor/Iterator With this new found knowledge, we could also explore data structures that don’t exist in Flex today, but could. One data structure in particular is really fantastic when you need to do frequent inserts/deletes or simply move through the values sequentially, a linked list.
  47. 47. Linked List A linked list is a data structure that is just a sequence of pieces of data, often called nodes. Linked lists can be implemented in a single fashion, where each node only knows about the next, or, in a double fashion where each node knows who came before it and who came after it
  48. 48. Linked List Each node in this linked list knows about who is sequentially before it, and who is sequentially after. They don’t have any information about the other nodes
  49. 49. Inserting List This makes the process of inserting into a list extremely efficient. There is no need to move any of the existing nodes, you simply change who (in this case) Pete and Andy believe are next and previous.
  50. 50. Deleting List Deleting is equally as efficient. In this case when we chose to remove Andy, we simply change the previous and next of Pete and Thomas
  51. 51. Andy is GCed Eventually in the future, the garbage collector ruthlessly slaughters Andy. However, that is not the concern of this session.
  52. 52. Searching List Searching an unsorted list takes about the same effort as searching an Array.
  53. 53. Searching By Index Where linked lists are much slower is when you need to find an item at a particular index. For an array, that is a very fast operation. Here it requires a walk through the list.
  54. 54. Working with Cursors The paradigm used by cursors, however, works very well with lists where we generally are moving between nodes
  55. 55. Results For good measure, let’s take a look at some data
  56. 56. Q&A Seriously? You must have some questions by now?
  57. 57. Resources Blog Aggregator (All of the Digital Primates) My Blog Specifically Follow Me on Twitter mlabriola