Note: This page is not yet complete and has some sections marked TBD. But there's plenty here to get you started!
Introduction
This document lays out the coding standards for writing open-source Flex framework components in ActionScript 3. Adhering to these standards makes the source code look consistent, well-organized, and professional.
Some of these standards are completely arbitrary, since there is not always a “best way” to code. Nevertheless, in the interest of consistency, *all commits to the Flex SDK project will be expected to follow these conventions*.
Code conventions are important. Code reviewers should point out when code doesn't follow the conventions. If there are disagreements, they can be discussed and the conventions adjusted but following the conventions is not optional.
Naming
Choosing good names is critical to creating code that is easy to use and easy to understand. You should always take the time to think about whether you have chosen the right name for something, especially if it is part of the public API.
Our naming standards are mostly consistent with those of ECMAScript and Flash Player 9.
Abbreviations
Avoid them as a general rule. For example, calculateOptimalValue() is a better method name than calcOptVal().
Being clear is more important than minimizing keystrokes. And if you don't abbreviate, developers won't have to remember whether you shortened a word like “qualified” to “qual” or “qlfd”.
However, we have standardized on a few abbreviations:
- acc for accessibility, as in
ButtonAccImpl - auto for automatic, as in
autoLayout - eval for evaluate, as in
EvalBindingResponder - impl for implementation, as in
ButtonAccImpl - info for information, as in
GridRowInfo - num for number of, as in
numChildren - min for minimum, as in
minWidth - max for maximum, as in
maxHeight - nav for navigation, as in
NavBar - regexp for regular expression, as in
RegExpValidator - util for utility, as in
StringUtil
This list probably does not include all abbreviations that are currently in use. If you're considering using an abbreviation that isn't listed here, please search the source code to determine whether it is already in use. If you don't find it, think twice about whether abbreviating is really appropriate.
Occasionally we are (deliberately) inconsistent about abbreviations. For example, we spell out “horizontal” and “vertical” in most places, such as horizontalScrollPolicy and verticalScrollPolicy but we abbreviate them to H and V in the very-commonly-used container names HBox and VBox.
Acronyms
Various acronyms are common in Flex, such as AIR, CSS, HLOC, IME, MX, MXML, RPC, RSL, SWF, UI, UID, URL, WSDL, and XML.
An acronym is always all-uppercase or all-lowercase (e.g., SWF or swf, but never Swf). The only time that all-lowercase is used is when the acronym is used by itself as an identifier, or at the beginning of an identifier, and the identifier should start with a lowercase letter. See the rules below for which identifiers should start with which case.
Examples of identifiers with acronyms are CSSStyleDeclaration, IUID, uid, IIME, and imeMode.
Word boundaries
When an identifier contains multiple words, we use two ways of indicating word boundaries: intercaps (as in LayoutManager or measuredWidth) and underscores (as in object_proxy). See the rules below for which method to use.
Sometimes it isn't clear whether a word combination has become its own single word, and we are unforunately inconsistent about this in some places: dropdown, popUp, pulldown.
Follow the acronym-casing rules even in the rare case that two acronyms must be adjacent. An example (which isn't actually in use) would be something like loadCSSURL(). But try to avoid such names.
Type-specifying names
If you want to incorporate the type into the name, make it the last “word”. Don't use the old ActionScript 1 convention of concatenating abbreviated type suffixes such as _mc to indicate type. For example, name a border Shape border, borderSkin, or borderShape, but not 'border_mc'.
Often, the best name for an object is simply the same as its type, with different casing:
var button:Button = new Button();
Package names
Start them with a lowercase letter and use intercaps for subsequent words: 'controls', 'listClasses'.
Package names should always be nouns or gerunds (the -ing noun form of a verb), not verbs, adjectives, or adverbs.
A package implementing lots of similar things should have a name which is the plural form of the thing: 'charts', 'collections', 'containers', 'controls', 'effects', 'events', 'formatters', 'managers', 'preloaders', 'resources', 'skins', 'states', 'styles', 'utils', 'validators'.
It is common to use a gerund for the name of a package which implements a concept: 'binding', 'logging', 'messaging', 'printing'. Otherwise, they are generally "concept nouns": 'accessibility', 'core', 'graphics', 'rpc'.
A package containing classes that support component 'FooBar' should be called 'fooBarClasses'.
File names
For importable APIs, the file name must be the same as the public API inside. But include files don't have to follow this rule.
Start the names of include files for 'Style(...)' metadata with an uppercase letter, use intercaps for subsequent words, and make the last word “Styles”: 'BorderStyles.as', 'ModalTransparencyStyles.as'.
Start the names of individual asset files with a lowercase letter and use underscores between words: 'icon_align_left.png'.
Namespace names
Start them with a lowercase letter and use underscores between words: 'mx_internal', 'object_proxy'.
Interface names
Start them with I and use intercaps for subsequent words: 'IList', 'IFocusManager', 'IUID'.
Class names
Start them with an uppercase letter and use intercaps for subsequent words: 'Button, FocusManager', 'UIComponent'.
Name 'Event' subclasses 'FooBarEvent'. Name 'Error' subclasses 'FooBarError'. Name the 'EffectInstance' subclass associated with effect 'FooBar' 'FooBarInstance'. Name 'Formatter' subclasses 'FooBarFormatter'. Name 'Validator' subclasses 'FooBarValidator'. Name skinning classes 'FooBarBackground', 'FooBarBorder', 'FooBarSkin', 'FooBarIcon', 'FooBarIndicator', 'FooBarSeparator', 'FooBarCursor', etc. Name utility classes 'FooBarUtil' (not 'FooBarUtils'; the package is plural but the class is singular).
It is common to name a base class 'FooBarBase': 'ComboBase', 'DateBase', 'DataGridBase', 'ListBase'.
Event names
Start them with a lowercase letter and use intercaps for subsequent words: '"move"', '"creationComplete"'.
Style names
Start them with a lowercase letter and use intercaps for subsequent words: 'color', 'fontSize'.
Enumerated values for String properties
Start them with a lowercase letter and use intercaps for subsequent words: '"auto"', '"filesOnly"',
Constant names
Use all uppercase letters with underscores between words: 'OFF', 'DEFAULT_WIDTH'.
The words in the identifier must match the words in the constant value if it is a String:
public static const FOO_BAR:String = "fooBar";
Property (variable and getter/setter) names
Start them with a lowercase letter and use intercaps for subsequent words: 'i', 'width', 'numChildren'.
Use 'i' for a loop index and 'n' for its upper limit. Use 'j' for an inner loop index and 'm' for its upper limit.
for (var i:int = 0; i < n; i++)
{
for (var j:int = 0; j < m; j++)
{
...
}
}
Use 'p' (for “property”) for a 'for-in' loop variable:
for (var p:String in o)
{
...
}
If a class overrides a getter/setter and wants to continue to expose the base getter/setter, it should do so by implementing a property whose name is the base name with a $ prepended. This getter/setter should be marked 'final' and should do nothing more than call the supergetter/setter.
mx_internal final function get $numChildren():int
{
return super.numChildren;
}
Storage variable names
Give the storage variable for the getter/setter 'foo' the name '_foo'.
Method names
Start them with a lowercase letter and use intercaps for subsequent words: 'measure()', 'updateDisplayList()'.
Method names should always be verbs.
Parameterless methods should generally not be named 'getFooBar()' or 'setFooBar()'; these should be implemented as getter/setters instead. However, if 'getFooBar()' is a slow method requiring a large amount of computation, it should be named 'findFooBar()', 'calculateFooBar()', 'determineFooBar()', etc. to suggest this, rather than being a getter.
If a class overrides a method and wants to continue to expose the base method, it should do so by implementing a method whose name is the base name with a $ prepended. This method should be marked 'final' and should do nothing more than call the supermethod.
mx_internal final function $addChild(child:DisplayObject):DisplayObject
{
return super.addChild(child);
}
Event handler names
Event handlers should be named by concatenating “Handler” to the type of the event: 'mouseDownHandler()'.
If the handler is for events dispatched by a subcomponent (i.e., not 'this'), prefix the handler name with the subcomponent name and an underscore: 'textInput_focusInHandler().'
Argument names
Use 'value' for the argument of every setter:
Do this:
public function set label(value:String):void
Not this:
public function set label(lab:String):void
Or this:
public function set label(labelValue:String):void
Or this:
public function set label(val:String):void
Use 'event' (not 'e', 'evt', or 'eventObj') for the argument of every event handler:
protected function mouseDownHandler(event:Event):void
Resource bundle names
If a resource bundle contains resources for a particular package, name the bundle the same as the package: 'controls, {formatters}}, validators'.
Resource key names
Start them with a lowercase letter and use intercaps for subsequent words: 'pm', 'dayNamesShort'.
Miscellaneous nomenclature
Avoid “object” because it is vague.
An “item” is a data item, not a DisplayObject.
A “renderer” is a DisplayObject that displays a data item.
A “type” is an AS3 type; use "kind" otherwise.
Language Usage
This section discusses how we use the language constructs of ActionScript 3, especially when there are multiple ways to express the same thing.
Compilation options
Compile with the options '-strict' and '-show-actionscript-warnings'. (These are the defaults in the flex-config.xml file.)
Property-based APIs
Favor property-based APIs rather than method-based APIs, because these are more suitable for declarative-style MXML programming.
Type declarations
Write a type annotation for every constant, variable, function argument, and function return value, even if the annotation is simply :* to indicate “no type”.
Do this:
var value:*;
Not this:
var value;
Use the narrowest type that is appropriate. For example, a loop index should be a 'int', not a 'Number', and certainly not an 'Object' or '*'. As another example, a 'mouseDownHandler' should declare its argument as 'event:MouseEvent', not 'event:Event'.
Use 'int' for integers, even if they can't be negative. Use 'uint' only for RGB colors, bit masks, and other non-numeric values.
Use '*' only if the value can be 'undefined'. You should generally use 'Object' rather than '*', with 'null' being the “object doesn't exist” value.
If you declare something to be of type 'Array', add a comment of the form '/* of ElementType */' immediately after 'Array' indicate the type of the array elements. A future version of the language is likely to have typed arrays.
Do this:
var a:Array /* of String */ = [];
Not this:
var a:Array = [];
And this:
function f(a:Array /* of Number */):Array /* of Object */
{
...
}
Not this:
function f(a:Array):Array
Literals
'undefined'
Avoid using this when possible. It is only necessary when dealing with values whose compile-time is type is '', and you should be using '' sparingly as well.
'int' and 'uint' literals
Do not use a decimal point in a integer.
Do this:
2
Not this:
2.
Use a lowercase 'x' and uppercase 'A-Z' in hexadecimal numbers.
Do this:
0xFEDCBA
Not this:
0Xfedcba
Always write an RGB color as a six-digit hexadecimal number.
Do this:
private const BLACK:uint = 0x000000;
Not this:
private const BLACK:uint = 0;
When dealing with indices, use the value '-1' to mean “no index”.
'Number' literals
If a Number value typically can be fractional, indicate this by using a decimal point, and follow the decimal point by a single trailing zero.
Do this:
alphaFrom = 0.0;
alphaTo = 1.0;
Not this:
alphaFrom = 0;
alphaTo = 1;
However, don't do this for pixel coordinates, which are by convention integral even though they can in principle be fractional.
Do this:
var xOffset:Number = 3;
Not this:
var xOffset:Number = 3.0;
Use 'e', not 'E', when using exponential notation.
Do this:
1.0e12
Not this:
1.0E12
Use the default value 'NaN' as the “not set” value for a 'Number'.
'String' literals
Use quotation marks (double quotes), not apostrophes (single quotes), to delimit strings, even if that string contains a quotation mark as a character.
Do this:
"What's up, \"Big Boy\"?"
Not this:
'What\'s up, "Big Boy"?'
Use '\u', not '\U', for unicode escape sequences.
'Array' literals
Use Array literals rather than 'new Array()'.
Do this:
[]
Not this:
new Array()
And this:
[ 1, 2, 3 ]
Not this:
new Array(1, 2, 3)
Use the Array constructor only to allocate an array of a prespecified size, as in 'new Array(3)', which means '[ undefined, undefined, undefined ]', not '[ 3 ]'.
'Object' literals
Use Object literals rather than 'new Object()'.
Do this:
{}
Not this:
new Object()
And this:
o = { a: 1, b: 2, c: 3 };
Not this:
o = new Object();
o.a = 1;
o.b = 2;
o.c = 3;
Or this:
o = {};
o.a = 1;
o.b = 2;
o.c = 3;
'Function' literals
Avoid using function literals to define anonymous functions; use a class method or package function instead.
If you must use a function literal, declare a return type, and terminate the last statement inside the function block with a semicolon.
Do this:
function(i:int):void { doIt(i - 1); doIt(i + 1); }
Not this:
function(i:int) { doIt(i - 1); doIt(i + 1) }
'RegExp' literals
Use the literal notation rather than constructing a 'RegExp' instance from a 'String'.
Do this:
var pattern:RegExp = /\d+/g;
Not this:
var pattern:RegExp = new RegExp("\\d+", "g");
'XML' and 'XMLList' literals
Use the literal notation rather than constructing an 'XML' instance from a 'String'.
Do this:
var node:XML = <name first="Jane" last="Doe"/>;
Not this:
var node:XML = new XML("<name first=\"Jane\" last=\"Doe\"/>");
Use double-quotes rather than single-quotes around XML attribute values:
Do this:
var node:XML = <name first="Jane" last="Doe"/>;
Not this:
var node:XML = <name first='Jane' last='Doe'/>;
'Class' literals
Use a fully-qualified class literal only if necessary to disambiguate between two imported classes with the same unqualified name.
Do this:
import mx.controls.Button;
...
var b:Button = new Button();
Not this:
import mx.controls.Button;
...
var b:Button = new mx.controls.Button();
But here a fully-qualified name is required and therefore qppropriate:
import mx.controls.Button;
import my.controls.Button;
...
var b:Button = new mx.controls.Button();
Expressions
Parentheses
Don't use unnecessary parentheses with common operators such as +, -, *, /, &&, ||, <, <=, >, >=, ==, and !=.
Do this:
var e:Number = a * b / (c + d);
Not this:
var e:Number = (a * b) / (c + d);
And this:
var e:Boolean = a && b || c == d;
Not this:
var e:Boolean = ((a && b) || (c == d));
The precedence rules for other operators are harder to remember, so parentheses can be helpful with them.
Coercion
Don't compare a Boolean value to 'true' or 'false'; it already is one or the other.
Do this:
if (flag)
Not this:
if (flag == true)
Do this:
var flag:Boolean = a && b;
Not this:
var flag:Boolean = (a && b) != false;
Explicitly coerce a 'Number', 'String', 'XML', 'XMLList', 'Array', 'Object', or '*' to a 'Boolean', because these types have multiple values which might reasonably be thought to coerce to 'false' and it is difficult to remember which ones actually do coerce to false in AS3.
Type |
Can you remember which of these values coerce to false? |
|---|---|
Number |
|
String |
|
XML / XMLList |
|
Array |
|
Object |
|
|
|
Do this:
if (s != null && s != "")
Not this:
if (s)
Subclasses of 'Object' (e.g., 'UIComponent') can coerce implicitly to Boolean, because it is obvious that only the 'null' value coerces to 'false' and all others coerce to 'true'. It's OK to explicitly compare the object to 'null' as required in Java. (Note: Object and its subclasses cannot store the value 'undefined'.)
Do this:
if (child)
Or this:
if (child == null)
And this:
if (!child)
Or this:
if (child != null)
For 'int' and 'uint', it is obvious that only the 0 value coerces to 'false' and all others coerce to 'true'. So if you want to use implicit coercion, it's OK but a comparison against 0 reads more nicely.
Do this:
if (num != 0)
Or this:
if (num)
And this:
if (num == 0)
Or this:
if (!num)
Prefer the use of a cast to the use of the 'as' operator. Use the 'as' operator only if the coercion might fail and you want the expression to evaluate to 'null' instead of throwing an exception.
Do this:
IUIComponent(child).document
Not this:
(child as IUIComponent).document
Comparison
Write comparisons in the order that they read most naturally:
Do this:
if (n == 3) // "if n is 3"
Not this:
if (3 == n) // "if 3 is n"
'++' and '--' operators
In cases where the postfix and prefix forms are equivalent, use the postfix form. Use the prefix form only when you need to use the value before it is incremented.
Do this:
for (var i:int = 0; i < n; i++)
Not this:
for (var i:int = 0; i < n; ++i)
Ternary operator
Use a ternary operator in place of a simple 'if'/'else' statement, especially for 'null' checks:
Do this:
return item ? item.label : null;
Not this:
if (!item)
return null;
return item.label;
But don't use nested ternary operators in place of complex 'if'/'else' logic.
Do this:
if (a < b)
return -1;
else if (a > b)
return 1;
return 0;
Not this:
return a < b ? -1 : (a > b ? 1 : 0);
'new' operator
Use parentheses after the class reference, even if the constructor takes no arguments.
Do this:
var b:Button = new Button();
Not this:
var b:Button = new Button;
Statements
Terminate each statement with a semicolon. Do not use the optional-semicolon feature of ActionScript 3.
Do this:
a = 1;
b = 2;
c = 3;
Not this:
a = 1
b = 2
c = 3
'include' statements
Use 'include', not the deprecated '#include'. Terminate the include statement with a semicolon, like any other statement.
Do this:
include "../core/ComponentVersion.as";
Not this:
#include "../core/ComponentVersion.as"
Use relative, not absolute, paths.
'import' statements
Import specific classes, interfaces, and package-level functions rather than using the * wildcard.
Do this:
import mx.controls.Button;
import flash.utils.getTimer;
Not this:
import mx.core.*;
'use namespace' statements
Use them. Do not use :: syntax on each reference to something in a non-open namespace.
Do this:
import mx.core.mx_internal;
use namespace mx_internal;
// Later, in some method...
doSomething();
Not this:
import mx.core.mx_internal;
// Later, in some method...
mx_internal::doSomething();
'if' statements
If the various branches of an if/else statement involve single statements, don't make them into blocks.
Do this:
if (flag)
doThing1();
Not this:
if (flag)
{
doThing1();
}
And this:
if (flag)
doThing1();
else
doThing2():
Not this:
if (flag)
{
doThing1();
}
else
{
doThing2();
}
But if any branch has multiple statements, make all of them into blocks.
Do this:'
if (flag)
{
doThing1();
}
else
{
doThing2();
doThing3();
}
Not this:
if (flag)
doThing1();
else
{
doThing2();
doThing3();
}
When doing multiple error checks, use sequential if statements that test for failure and return early. The successful execution flow is then down the page, with the succesful return at the end of the method. Do not use nested tests for success, which make the execution flow drift across the page.
Do this:
if (!condition1)
return false;
...
if (!condition2)
return false;
...
if (!condition2)
return false;
...
return true;
Not this:
if (condition1)
{
...
if (condition2)
{
...
if (condition3)
{
...
return true;
}
}
}
return false;
'for' statements
Make the body of a 'for' loop be a block, even if it consists of only one statement.
Do this:
for (var i:int = 0; i < 3; i++)
{
doSomething(i);
}
Not this:
for (var i:int = 0; i < 3; i++)
doSomething(i);
Store the upper limit for a 'for'-loop variable in a local variable so that it isn't re-evaluated every time through the loop (unless, of course, it needs to be re-evaluated on each interation).
Do this:
var n:int = a.length;
for (var i:int = 0; i < n; i++)
{
...
}
Not this:
for (var i:int = 0; i < a.length; i++)
{
...
}
Declare the loop var inside the parentheses of the 'for' statement, unless it is reused elsewhere.
Do this:
for (var i:int = 0; i < 3; i++)
Not this:
var i:int;
for (i = 0; i < 3; i++)
{
...
}
'while' statements
Make the body of a 'while' loop be a block, even if it consists of only one statement.
Do this:
while (i < n)
{
doSomething(i);
}
Not this:
while (i < n)
doSomething(i);
'do' statements
Make the body of a 'do' loop be a block, even if it consists of only one statement.
Do this:
do
{
doSomething(i);
}
while (i < n);
Not this:
do
doSomething(i);
while (i < n);
'switch' statements
Make the body of each 'case' clause, and of the 'default' clause, be a block. Put the 'break' or 'return' statement within the block, not after it. If you are returning, don't put a 'break' after the 'return'. Treat the default clause similarly to the case clauses; 'break' or 'return' from it rather than falling through the bottom of the 'switch'.
Do this:
switch (n)
{
case 0:
{
foo();
break;
}
case 1:
{
bar();
return;
}
case 2:
{
baz();
return;
}
default:
{
blech();
break;
}
}
Not this:
switch (n)
{
case 0:
foo();
break;
case 1:
{
bar();
}
break;
case 2:
baz();
return;
break;
default:
blech();
}
'return' statements
Do not enclose a return value in unnecessary parentheses.
Do this:
return n + 1;
Not this:
return (n + 1);
Returning from the middle of a method is OK.
Declarations
Don't declare multiple constants or variables in a single declaration.
Do this:
var a:int = 1;
var b:int = 2;
Not this:
var a:int = 1, b:int = 2;
The 'override' keyword
If present, put this first, before the access specifier.
Do this:
override protected method measure():void
Not this:
protected override method measure():void
Access specifiers
Put an explicit access specifier everywhere that one is allowed. Do not use the fact that 'internal' is the implicit access specifier if none is written.
Before making an API 'public' or 'protected', think hard about whether it is really needs to be. Public and protected APIs must be documented. They must also be supported for several releases before being formally deprecated.
The 'static' keyword
If present, put this after the access specifier.
Do this:
public static const MOVE:String = "move"
Not this:
static public const MOVE:String = "move";
The 'final' keyword
If present, put this after the access specifier.
Do this:
public final class BoxDirection
Not this:
final public class BoxDirection
Declare all “enum classes” to be final.
Also declare “base” properties and methods (those starting with '$') to be final.
Constants
All constants should be static. There is no reason to use an instance constant, since all instances would store the same value.
Do this:
public static const ALL:String = "all";
Not this:
public const ALL:String = "all";
Variables
If a variable needs to be initialized to a non-default value, do this in the declaration, not in the constructor.
Do this:
private var counter:int = 1;
Not this:
private var counter:int;
...
public function MyClass()
{
super();
...
counter = 1;
}
Local variables
Declare local variables at or just before the point of first use. Don't declare them all at the top of the function.
Do this:
private function f(i:int, j:int):int
{
var a:int = g(i - 1) + g(i + 1);
var b:int = g(a - 1) + g(a + 1);
var c:int = g(b - 1) + g(b + 1);
return (a * b * c) / (a + b + c);
}
Not this:
private function f(i:int, j:int):int
{
var a:int;
var b:int;
var c:int;
a = g(i - 1) + g(i + 1);
b = g(a - 1) + g(a + 1);
c = g(b - 1) + g(b + 1);
return (a * b * c) / (a + b + c);
}
Declare local variables only one per function. ActionScript 3 doesn't have block-scoped locals.
Do this:
var a:int;
if (flag)
{
a = 1;
...
}
else
{
a = 2;
...
}
Not this:
if (flag)
{
var a:int = 1;
...
}
else
{
var a:int = 2;
...
}
And this:
var i:int;
for (i = 0; i < n; i++)
{
...
}
for (i = 0; i < n; i++)
{
...
}
Not this:
for (var i:int = 0; i < n; i++)
{
...
}
for (var i:int = 0; i < n; i++)
{
...
}
Classes
If a class simply extends 'Object', omit the 'extends Object' clause.
The only “bare statements” in a class should be calls to static class initialization methods, such as 'loadResources()'.
Constructors
If a classes has instance members, write a constructor, and make it explicitly call 'super()', even if it does nothing else.
If the constructor takes arguments that set instance vars, give the the same names as the instance vars.
Do this:
public function MyClass(foo:int, bar:int)
{
super();
this.foo = foo;
this.bar = bar;
}
Not this:
public function MyClass(fooVal:int, barVal:int)
{
super();
foo = fooVal;
bar = barVal;
}
Don't set the classes' instance vars in the constructor; do this in the declarations of the instance vars. However, if you need to reset the values of inherited instance vars, do this in the consturctor.
Interfaces
TBD
Namespaces
TBD
Implementing properties
TBD
Metadata
TBD
Packages
One public API (usually a class, sometimes a namespace or function) inside the package statement.
Helper classes
bare statements
File Organization
This section presents the order in which a Flex framework file should be organized.
File template
When creating a new Flex component the File Template for Flex Components should be used so that the class is organized in the correct order. Unused sections can be deleted.
Copyright notice
Include a copyright notice at the top of every file (.as, .mxml, .xml) in the framework
//////////////////////////////////////////////////////////////////////////////// // // Licensed to the Apache Software Foundation (ASF) under one or more // contributor license agreements. See the NOTICE file distributed with // this work for additional information regarding copyright ownership. // The ASF licenses this file to You under the Apache License, Version 2.0 // (the "License"); you may not use this file except in compliance with // the License. You may obtain a copy of the License at // // http://www.apache.org/licenses/LICENSE-2.0 // // Unless required by applicable law or agreed to in writing, software // distributed under the License is distributed on an "AS IS" BASIS, // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. // See the License for the specific language governing permissions and // limitations under the License. // ////////////////////////////////////////////////////////////////////////////////
Note that it is 80 characters wide.
package statement
TBD
import statements
TBD
use namespace statement
TBD
Class metadata
Organize the class metadata into sections, in the order Events, Styles, Effects, Excluded APIs, and Other Metadata.
Put a minor section header before each section. Note that the minor section headers are 40 characters wide and that there are two spaces between the // and the section name.
Alphabetize the metadata by name="..." within each section. In the Other Metadata section, alphabetize them by metadata tag name.
//--------------------------------------
// Events
//--------------------------------------
/
**
* ASDoc comment.
*/
[Event
/**
* ASDoc comment.
*/
[Event
//--------------------------------------
// Styles
//--------------------------------------
/**
* ASDoc comment.
*/
[Style
/**
* ASDoc comment.
*/
[Style]
//--------------------------------------
// Effects
//--------------------------------------
/**
* ASDoc comment.
*/
[Effect
/**
* ASDoc comment.
*/
[Effect]
//--------------------------------------
// Excluded APIs
//--------------------------------------
[Exclude(name="horizontalAlign", kind="style")]
[Exclude(name="verticalAlign", kind="style")]
//--------------------------------------
// Other metadata
//--------------------------------------
[DefaultBindingProperty(source="text", destination="text")]
[IconFile("Text.png")]
Class declaration
TBD
include statement for Version.as
Every class should include core/Version.as using a relative path. This file contains the declaration for 'static const VERSION:String'.
include "../core/Version.as";
Implementation notes
TBD
Class initialization
TBD
Class constants
Put 'static const' declarations here.
ActionScript 3 does not allow a constant to have type 'Array' or 'Object'. Declare such constants using 'static var' rather than 'static const', but put them in this section because they are conceptually constants.
Class mix-ins
Declare any static variables of type 'Function' that get mixed in rather than being declared as methods.
Class resources
TBD
Class variables
TBD
Class properties
Declare static getters and setters here. Order them alphabetically by property name. Use a minor separator with the property name for each one. Put the getter before the setter.
Class methods
Put 'static function' declarations here.
Constructor
TBD
Variables
TBD
Overridden properties
Put overrides of non-static getters and setters here. Order them alphabetically by property name. Use a minor separator with the property name for each one. Put the getter before the setter.
Properties
Put new non-static getters and setters here. Order them alphabetically by property name. Use a minor separator with the property name for each one. Put the getter before the setter.
Overridden methods
Put overrides of non-static functions here.
Methods
Put new non-static functions here.
Overridden event handlers
Put overrides of event handlers here.
Event handlers
Put new event handlers here.
Out-of-package helper classes
TBD
Formatting
This section covers how a Flex framework class should be formatted.
Line width
The target line length is 80-characters per line although up to 100-characters per line is permissible.
The most important factor to consider is readability.
FlashBuilder should be configured to show the print margin column (Preferences->General->Editors->Text Editors->Print Margin Column) so the line width is not exceeded.
Indentation
Use 4-space indentation. Configure your text editor to insert spaces rather than tabs. This allows another program that uses a different indentation setting, such as Notepad with its 8-character indents, to display the code without disfiguring it.
Section separators
The major section separators inside a class look like this:
//--------------------------------------------------------------------------
//
// Overridden methods
//
//--------------------------------------------------------------------------
They extend from column 4 through column 80. The text is indented to column 8.
The minor section separators inside a class, such as between properties, look like this:
//----------------------------------
// visible
//----------------------------------
They extend from column 4 through column 40. The text is indented to column 8.
Put a single blank line above and below the separators.
Separation of declarations
Use a single blank line as a vertical separator between constant, variable, or function declarations.
/**
* @private
* Holds something.
*/
var a:Number;
/**
* @private
*/
var b:Number
Metadata
TBD
Do this:
Inspectable[a="1", b="2"]
Not this:
Inspectable[a=1 b=2]
Array indexing
Don't put any spaces before or after the left bracket or before the right bracket.
Do this:
a[0]
Not this:
a[ 0 ]
Commas
Follow a comma with a single space. This applies to argument lists, array literals, and object literals.
Array literals
Put a single space after the left bracket and a single space before the right bracket, and put a single space after (but none before) each comma.
Do this:
[ 1, 2, 3 ]
Not these:
[1, 2, 3]
[1,2,3]
An empty array is a special case.
Do this:
[]
Not this:
[ ]
Format lengthy array initializers requiring multiple lines with aligned brackets:
static var numberNames:Array /* of String */ =
[
"zero",
"one",
"two",
"three",
"four",
"five",
"six",
"seven",
"eight",
"nine"
];
Object literals
Put a single space after the left brace and a single space before the right brace, and put a single space after the colon separating the property name and value.
Do this:
{ a: 1, b: 2, c: 3 }
Not these:
{a: 1, b: 2, c: 3}
{a:1, b:2, c:3}
{a:1,b:2,c:3}
An empty Object is a special case.
Do this:
{}
Not this:
{ }
Format lengthy object initializers requiring multiple lines with aligned braces:
private static var TextStyleMap:Object =
{
color: true,
fontFamily: true,
fontSize: true,
fontStyle: true,
fontWeight: true,
leading: true,
marginLeft: true,
marginRight: true,
textAlign: true,
textDecoration: true,
textIndent: true
};
Function literals
TBD
var f:Function;
f = function():void
{
doSomething();
};
Type declarations
Don't put any spaces before or after the colon that separates a variable, parameter, or function from its type.
Do this:
var n:Number;
Not these:
var n : Number;
var n: Number;
And this:
function f(n:Number):void
Not these:
function f(n : Number) : void
function f(n: Number): void
Operators and assignments
Put a single space around the assignment operator.
Do this:
a = 1;
Not this:
a=1;
Put a single space around infix operators.
Do this:
a + b * c
Not this:
a+b*c
Put a single space around comparison operators.
Do this:
a == b
Not this:
a==b
Don't put any spaces between a prefix operator and its operand.
Do this:
!o
Not this:
! o
Don't put any spaces between a postfix operator and its operand.
Do this:
i++
Not this:
i ++
Statements
Start each statement on a new line, so that you can set a breakpoint on any statement.
Do this:
a = 1;
b = 2;
c = 3;
Not this:
a = 1; b = 2; c = 3;
Align the braces of statement blocks.
Do this:
function f():void
{
var n:int = numChildren;
for (var i:int = 0; i < n; i++)
{
if ()
{
x = horizontalGap * i;
y = verticalGap * i;
}
}
}
Not this:
function f():void {
var n:int = numChildren;
for (var i:int = 0; i < n; i++) {
if () {
x = horizontalGap * i;
y = verticalGap * i;
}
}
}
Variable declarations
TBD
Constant declarations
Use the const keyword for values that are unmodifiable.
Do this:
const vsp:String = getStyle("verticalScrollPolicy");
Or this:
const dataProvider:ICollectionView = this.dataProvider as ICollectionView;
Avoid calculations and method calls in loops.
Do this:
const myArrayLength:int = myArray.length;
for (var i=0; i < myArrayLength; i++)
{
}
Not this:
for (var i=0; i < myArray.length; i++)
{
}
Function declarations
TBD
Do this:
f(a, b)
Not these:
f(a,b)
f( a, b )
If the parameters have to wrap, indent the subsequent lines after the left parenthesis. Put multiple parameters per line if they fit. Otherwise, put one per line. If even one won't fit, put the first one on the second line, indented past the beginning of the function name.
public function foo(parameter1:Number, parameter2:String,
parameter3:Boolean):void
public function foo(parameter1:Number,
parameter2:String,
parameter3:Boolean):void
public function aVeryLongFunctionName(
parameter1:Number, parameter2:String,
parameter3:Boolean):void
Function calls
TBD
Do this:
f(a, b)
Not these:
f(a,b)
f( a, b )
'if' statements
Follow the 'if' keywords with a single space before the left parenthesis. Don't put any spaces after the left parenthesis or before the right parenthesis.
Do this:
if (a < b)
Not these:
if(a < b)
if( a < b )
if ( a < b )
else if ?
multiline ?
'for' statements
Follow the 'for' keyword with a single space before the left parenthesis. Don't put any spaces after the left parenthesis or before the right parenthesis.
Do this:
for (var i:int = 0; i < n; i++)
Not these:
for(var i:int = 0; i < n; i++)
for( var i:int = 0; i < n; i++ )
for ( var i:int = 0; i < n; i++ )
If the 'for' clause needs to wrap, indent the subsequent lines after the left parenthesis.
for (var aLongLoopVariableName:int = aLongInitialExpression;
aLongLoopVariableName < aLongUpperLimit;
aLongLoopVariableName++)
'switch' statements
Follow the 'switch' keyword with a single space before the left parenthesis. Don't put any spaces after the left parenthesis or before the right parenthesis.
Do this:
switch (n)
Not these:
switch(n)
switch( n )
switch ( n )
Follow the 'switch' keyword with a single space before the left parenthesis. Don't put any spaces after the left parenthesis or before the right parenthesis.
Do this:
switch (n)
{
case 1:
{
a = foo();
break;
}
case 2:
{
a = bar();
break;
}
default:
{
a = blech();
break;
}
}
Not these:
switch(n)
switch( n )
switch ( n )
'class' and 'interface' declarations
braces are always balanced
no braces around single lines
single statement per line
Exceptions to formatting rules
It is permissible to deviate from the standard when modifying code that is not conformant to the standard. It is more important to be consistent with the style of the surrounding code.
ASDoc
Property comments
Only document the first function of a get/set function pair for a property. The idiom for defining and documenting a property is:
/**
* @private
* The backing variable for the property.
*/
private var _someProp:Foo;
/**
* Place all comments for the property with the getter which is defined first.
* Comments should cover both get and set behavior as appropriate.
*/
public function get someProp():Foo
{
...
}
/**
* @private
*/
public function set someProp(value:Foo):void
{
...
}
Also, ASDoc comments are applied to metadata tags as well as other constructs within a class so take care that your comments apply to the proper target. If you tag a property as Bindable, your property comment must precede the get function, not the Bindable metadata tag.
Do this:
[Bindable("somePropChanged")]
/**
* Comments for someProp
*/
public function get someProp():Foo
Not this:
/**
* Comments for someProp
*/
[Bindable("somePropChanged")]
public function get someProp():Foo
Using the private tag
Do not use the @private tag in ASDoc comments before private variables and private methods. They are not needed and they take up space.
General Guidelines
- Start each sentence in an ASDoc comment on a new line. It is easier to edit the ASDoc.
- Always close HTML tags in comments, including \<p>\</p> and \<code>\</code> tags.
- Do not use @return in a setter/getter. It is ignored.
- Do not use \<code> tags around a class name.
This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License
This text is adapted from Adobe Flex SDK Coding Conventions And Best Practices.