User manual MACROMEDIA FLEX 2-PROGRAMMING ACTIONSCRIPT 3.0

[. . . ] Programming ActionScript 3. 0 Adobe Flex 2 ® TM © 2006 Adobe Systems Incorporated. Flex 2 Programming ActionScript 3. 0 If this guide is distributed with software that includes an end-user agreement, this guide, as well as the software described in it, is furnished under license and may be used or copied only in accordance with the terms of such license. Except as permitted by any such license, no part of this guide may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, recording, or otherwise, without the prior written permission of Adobe Systems Incorporated. Please note that the content in this guide is protected under copyright law even if it is not distributed with software that includes an end-user license agreement. [. . . ] In each case, the overridden method adds a type check that prevents the addition of elements that are not the correct data type. Subsequently, each method calls the superclass version of itself. The push() method iterates through the list of arguments with a for. . in loop and does a type check on each argument. Any argument that is not the correct type is removed from the args array with the splice() method. After the for. . in loop ends, the args array contains values only of type dataType. The superclass version of push() is then called with the updated args array, as the following code shows: AS3 override function push(. . . args):uint { for (var i:* in args) { if (!(args[i] is dataType)) { args. splice(i, 1); } } return (super. push. apply(this, args)); } The concat() method creates a temporary TypedArray named passArgs to store the arguments that pass the type check. This allows the reuse of the type check code that exists in the push() method. A for. . in loop iterates through the args array, and calls push() on each argument. Because passArgs is typed as TypedArray, the TypedArray version of push() is executed. The concat() method then calls its own superclass version, as the following code shows: AS3 override function concat(. . . args):Array { var passArgs:TypedArray = new TypedArray(dataType); for (var i:* in args) { // type check done in push() passArgs. push(args[i]); } return (super. concat. apply(this, passArgs)); } Advanced Topics 247 The splice() method takes an arbitrary list of arguments, but the first two arguments always refer to an index number and the number of elements to delete. This is why the overridden splice() method does type checking only for args array elements in index positions 2 or higher. One point of interest in the code is that there appears to be a recursive call to splice() inside the for loop, but this is not a recursive call because args is of type Array rather than TypedArray, which means that the call to args. splice() is a call to the superclass version of the method. After the for. . in loop concludes, the args array contains only values of the correct type in index positions 2 or higher, and splice() calls its own superclass version, as shown in the following code: AS3 override function splice(. . . args):* { if (args. length > 2) { for (var i:int=2; i< args. length; i++) { if (!(args[i] is dataType)) { args. splice(i, 1); } } } return (super. splice. apply(this, args)); } The unshift() method, which adds elements to the beginning of an array, also accepts an arbitrary list of arguments. The overridden unshift() method uses an algorithm very similar to that used by the push() method, as shown in the following example code: AS3 override function unshift(. . . args):uint { for (var i:* in args) { if (!(args[i] is dataType)) { args. splice(i, 1); } } return (super. unshift. apply(this, args)); } } 248 Working with Arrays Example: PlayList The PlayList example demonstrates techniques for working with arrays, in the context of a music playlist application that manages a list of songs. These techniques are: Creating an indexed array Adding items to an indexed array Sorting an array of objects by different properties, using different sorting options Converting an array to a character-delimited string The PlayList application files can be found in the Samples/PlayList folder. The application consists of the following files: File PlayListApp. mxml com/example/programmingas3/playlist/ PlayList. as com/example/programmingas3/playlist/ Song. as com/example/programmingas3/playlist/ SortProperty. as Description The main application file in MXML for Flex. Provides the playlist functionality for the application, such as adding and sorting songs. A value object representing information about a single song. The items that are managed by the PlayList class are Song instances. A pseudo-enumeration whose available values represent the properties of the Song class by which a list of Song objects can be sorted. PlayList class overview The PlayList class manages a set of Song objects. It has public methods with functionality for adding a song to the playlist (the addSong() method) and sorting the songs in the list (the sortList() method). In addition, the class includes a read-only accessor property, songList, which provides access to the actual set of songs in the playlist. [. . . ] // Return a value to ActionScript; // the returned value must first be encoded as an XML-formatted string. _flashControl. SetReturnValue(encodedResponse); } The event object (e) has a request property (e. request) that is a string containing information about the function call, such as the function name and parameters, in XML format. This information can be used by the container to determine what code to execute. In the ExternalInterfaceProxy class, the request is converted from XML format to an ExternalInterfaceCall object, which provides the same information in a more accessible form. [. . . ]