1. Avoid the new operator when creating Arrays
var a = [];
NOT:
var a = new Array();
2. Arrays are expensive to create, do so conservatively
var vanityCollection01 : Array = new Array();
var vanityCollection02 : Array = new Array();
var vanityCollection03 : Array = new Array();
var vanityCollection04 : Array = new Array();
3. Fastest way to copy an array:
var copy : Array = sourceArray.concat();
4. Setting values in Arrays is slow
employees.push( employee );
employees[2] = employee;
5. Getting values from Arrays is twice as fast as setting
var employee : Employee = employees[2];
6. Use static for properties methods that do not require an object instance
StringUtils.trim( "text with space at end " );
Class definition:
package
{
public final class StringUtils
{
public static function trim( s : String ) : String
{
var trimmed : String;
// implementation...
return trimmed;
}
}
}
7. Use const for properties that will never change throughout the lifecycle of the application
public const APPLICATION_PUBLISHER : String = "Company, Inc.";
8. Use final when no subclasses need to be created of a class
public final class StringUtils
9. Length of method/variable names doesn't matter in ActionScript 3.0 (true in other langs)
someCrazyLongMethodNameDoesntReallyImpactPerformanceTooMuch();
10. One line assignments DO NOT buy any performance (true in other langs)
var i=0; j=10; k=200;
11. No difference in memory usage between an if statement and a switch statement
if ( condition )
{
// handle condition
}
IDENTICAL MEMORY USAGE:
switch ( condition ) { case "A": // logic to handle case A break; case "B": // logic to handle case B break; }
12. Rank your if statements in order of comparisons most likely to be true
if ( conditionThatHappensAlot ) { // logic to handle frequently met condition } else if ( conditionThatHappensSomtimes ) { // handle the case that happens occaisonally } else { // handle the case that doesn’t happen that often }
13. AVM promotes int to Number during calculations inside loops (VM has been changing, from 9 to 10, so int, uint and number conversions aren't as slow as they used to be.)
14. Resolve issues of promotion, unknown, or incorrect object types
15. Use uint sparingly, it can be slow (VM has been changing, from 9 to 10, so int, uint and number conversions aren't as slow as they used to be.)
var footerHex : uint = 0x00ccff;
16. Use integers for iterations
(var i: int = 0; i < n; i++) NOT for (var i: Number = 0; i < n; i++)
17. Don't use int with decimals
var decimal : Number = 14.654;
NOT:
var decimal : int = 14.654;
18. Multiply vs. Divide: instead of 5000/1000 use: 5000*0.001
19. Locally store function values in for and while statements instead of repeatedly accessing them
for (..){ a * 180 / Math.PI; } declare: toRadians = a*180/Math.PI; outside of the loop
20. Avoid calculations and method calls in loops
var len : int = myArray.lengh; for (var i=0;i<len;i++){}
NOT:
for (var i=0;i< myArray.lengh;i++){ }
21. Use RegEx for validation, use string methods for searching
// postal code validation example using regular expressions private var regEx:RegExp = /^[A-Z][0-9][A-Z] [0-9][A-Z][0-9]$/i; private function validatePostal( event : Event ) : void { if( regEx.test( zipTextInput.text ) ) { // handle invalid input case } } // search a string using String methods var string : String = "Search me"; var searchIndex : int = string.indexOf( "me" ); var search : String = string.substring( searchIndex, searchIndex + 2 );
22. Reuse objects to maintain a “memory plateau” DisplayObjects, URLLoader objects
23. Follow the Flex component model:
createChildren(); commitProperties(); updateDisplayList();
24. Only use Datagrids as a last resort (make sure you can’t implement in a regular List first)
25. Avoid Repeaters for scrollable data
26. Avoid the setStyle() method (One of the most expensive calls in the Flex framework)
27. Using too many containers dramatically reduces the performance of your application
<mx:Panel> <mx:VBox> <mx:HBox> <mx:Label text="Label 1" /> <mx:VBox> <mx:Label text="Label 2" /> </mx:VBox> <mx:HBox> <mx:Label text="Label 3" /> <mx:VBox> <mx:Label text="Label 4" /> </mx:VBox> </mx:HBox> </mx:HBox> </mx:VBox> </mx:Panel>
28. You do not need to always use a container tag as the top-level tag of components Totally valid component, no top level container needed:
<mx:Image xmlns:mx="http://www.adobe.com/2006/mxml" source="avatar.jpg" width="200" height="200" />
29. Remove unnecessary container wrappers to reduce container nesting
30. Avoid: The VBox container inside an tag, (eliminates redundancy)
<mx:Panel> <mx:Label text="Label 1" /> <mx:Label text="Label 2" /> </mx:Panel> <mx:Panel> <mx:VBox> <mx:Label text="Label 1" /> <mx:Label text="Label 2" /> </mx:VBox> </mx:Panel>
31. Avoid: VBox container inside an mx:Application tag, (eliminates redundancy)
<?xml version="1.0" encoding="utf-8"?> <mx:Application xmlns:mx=http://www.adobe.com/2006/mxml> <mx:Label text="Label 1" /> <mx:Label text="Label 2" /> </mx:Application>
NOT:
<?xml version="1.0" encoding="utf-8"?> <mx:Application xmlns:mx=http://www.adobe.com/2006/mxml> <mx:VBox> <mx:Label text="Label 1" /> <mx:Label text="Label 2" /> </mx:VBox> </mx:Application>
32. Set the recycleChildren property to true to improve a Repeater object's performance (re-uses previously created children instead of creating new ones)
<mx:Script> <![CDATA[ [Bindable] public var repeaterData : Array = ["data 1", "data 2"]; ]]> </mx:Script> <mx:Repeater id="repeater" dataProvider="{repeaterData}"> <mx:Label text="data item: {repeater.currentItem}"/> </mx:Repeater>
33. Keep framerate set at 60 fps or lower
<?xml version="1.0" encoding="utf-8"?> <mx:Application xmlns:mx=http://www.adobe.com/2006/mxml frameRate="45"> </mx:Application>
34. Avoid multiple display manipulations per frame
35. Code against ENTER_FRAME events instead of Timer events
public function onEnterFrame( event : Event ) : void { } private function init() : void { addEventListener( Event.ENTER_FRAME, onEnterFrame ); }
NOT:
public function onTimerTick( event : Event ) : void { } private function init() : void { var timer : Timer = new Timer(); timer.start(); timer.addEventListener( TimerEvent.TIMER, onTimerTick ); }
36. To defer object creation over multiple frames use:
<mx:Container creationPolicy="queued"/>
37. Alpha = 0 is not the same as visible = false (Objects marked invisible are passed over)
loginButton.visible = false;
NOT:
loginButton.alpha = 0;
关于消耗内存
我个人的看法是这样
少定义变量 减少内存消耗 但是加大CPU消耗
多定义变量 就相反过来
模块和组件 随用随加载 用完就卸载 （这个根据实际情况来弄）
监听能去掉就去掉 尽量复用已经存在的东西 包括Timer等
代码的效率
这个就得靠经验了
我不认为看几篇文章就能提高多少
算法越精细 程序运行效率就越高 代码量就越少
算法你可以理解为对一个业务逻辑的处理方法
这是代码量最大的地方
给你打个比方
if(a==2){
a=4;
}else{
a=6
｝
这个可以简单的写成
a = a==2?4:6;