Mar 30 2009

Learning design patterns with Actionscript 3: episode 2 – Decorator pattern

Category: actionscript — Davide Zanotti @ 2:21 am

The objective of the decorator pattern is to provide a way to add extra features and responsibilities to a class at runtime without to subclass it.

The classes diagram of this pattern is composed by an interface or an abstract class which will define the supertype of the class that will be extended (decorated) by one or more classes implementing the same interface and extending an abstract class which identify these as decorator classes.

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Mar 18 2009

Set DataGridColumn’s width in percentage with ease

Category: flex — Davide Zanotti @ 3:40 pm

I was trying to set the columns of a DataGrid to a certain percentage, but I discovered that inexplicably DataGridColumn doesn’t provide percentageWidth property nor it accepts a percentage string as width property… so I did a quick search on google and I found that is sad but true and moreover the solution I found on the web is to use a function to calculate each single column width after creationComplete event is dispatched… terrible! However I did a test before, by assign a decimal value to width (0.5 instead of 50%) and it works! The width property in fact accepts a Number as value not an int, so we can specify a value under 1, which is treated as a percentage… what surprise me, is that no one seems to had this idea… anyway I hope this will be helpful for all.

This is a piece of my AS code to set DataGridColumn width in percentage:

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col = new DataGridColumn();
col.width = options[i] == "Message" ? 0.6 : 0.1;

In my code I’m setting the columns to 10% and to 60% only for “Message” column.

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Mar 06 2009

parseInt(): difference between Javascript and Actionscript

Category: actionscript,javascript — Davide Zanotti @ 8:27 am

Today is the day of the little big discoveries. I realized that the parseInt() function, which objective is the same in both languages (Actionscript and Javascript), is a bit different between them. In Actionscript the function is based on base 10 numeration, in Javascript instead the funny thing is that it try to guess the radix by analyzing the string received as first argument, so if you want to be sure of the result returned you have to explicitly pass the radix in the second argument.

Example:

var myString = "000123";
alert(parseInt(myString));

The code above will alert 83 instead of 123 (because the default base guessed by Javascript isn’t 10 like in Actionscript), to get 123 the code must be:

var myString = "000123";
alert(parseInt(myString, 10));

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Feb 23 2009

Extending Flex’s logging framework to write custom log files

Category: flex — Davide Zanotti @ 11:19 am

In these days I played with Flex’s logging framework and I extended it to write log messages to files, both plain text .log files and dynamic HTML, CSS formatted and Javascript powered files with the ability to filter message type (debug, error, fatal and so on).

The logging framework is a powerful feature that comes with Flex’s sdk and it’s composed by the classes under mx.logging package, which includes the two “subpackages” mx.logging.errors and mx.logging.target.

Java developers should be already confident whit such framework, because logging api are commonly used in Java programming,  Actionscript /Flash/Flex developers may find this tool a novelty (as I did).

The objective of logging framework is to provide a tool that offers a far better, flexible and centralized way to debug an application than simple use a lot of trace() callings. With Flex’s debugging framework we are able to print and filtering among different types of message based on their severity, such:

  • DEBUG
  • ERROR
  • FATAL
  • INFO
  • WARN

We can also print the timestamp of the message and the class it refers to, and finally we can simultaneously print messages to different targets.

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Feb 12 2009

Converting Java to Actionscript… maybe is not so hard (I hope)

Category: actionscript — Davide Zanotti @ 5:06 am

After valuate my own realization of a certain library, I opted to try the porting of an already existent one… which is made in Java. This library has a lot of classes and interfaces and the manually translation would be very time-expensive, considering also that it uses a lot of classes and functions which are unavailable in Actionscript 3. Fortunately I found a small and useful AIR application which automatically converts .java files to .as files (the application is here: http://thunderhead.esri.com/readonlyurl/J2AS3.air), this application anyway helps a lot but many extra-work is required to properly convert the classes… for example Actionscript has not the abstract key, variable can’t be market as final and so on, so we have to manually adjust these issues. Another useful stuff I found is an Actionscript library which aim is to provide to AS3 developers the same (more or less) features and power of Java Collection framework, which provide classes like HashMap, ArrayList, LinkedList and so on (the library can be found here: http://code.google.com/p/addicted2flash/). Despite these helps I’m still facing some incompatibility issues… classes/methods AS3 is missing, but implementing them by myself is quite simple. For example I implemented the Java’s System.arraycopy() in 2 minutes, by following the JavaDoc ).

In conclusion Actionscript and Java have a  lot of stuff in common, the syntax and structure is quite the same, except for some issues like abstract classes and methods, multiple methods and constructors declaration (override). The main difference is that Java provides an huge number of Classes that Actionscript doesn’t, however it seems not so hard to translate Java code and implement Java functionality in Actionscript.

I hope I won’t have to deny my words :)

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