Most ActionScript developers are very familiar with Anonymous Objects in ActionScript 3.0 as they provide a convenient mechanism from which properties of an object which are not known at design time can be defined at runtime. This post is just a quick tip on the Object.setPropertyIsEnumerable() method, for more detailed information on using Objects in ActionScript 3.0 visit livedocs.

The Object class has a few useful methods, specifically toString();, hasOwnProperty(); and propertyIsEnumerable();. There is also another method of the Object class which is very useful: setPropertyIsEnumerable() which can be utilized to explicitly omit a property from being included in an enumeration of an object.

Consider the following example:

When enumerating the object instance all properties and their values can easily be retrieved, however it is important to keep in mind that when enumerating an Object the order in which properties are retrieved is not guaranteed. So executing the same loop against the same object instance could yield different results each time, such as “value B, value A, value C” as opposed to what you might have expected, i.e. “value A, value B, value C”.

Now suppose you do not want a property to be exposed via an enumeration of the object, this can be achieved via:

So based on the above examples, if we did not want to expose the “propA” property in a for in… loop we could omit the property as follows:

So when you need to omit properties from being included in an enumeration of an object, Object.setPropertyIsEnumerable(); proves very useful.

When working with the Adobe AIR SQL API it is important to consider the various best practices advocated by Adobe regarding performance, security and design. As there is nothing in particular in the SQL API itself to guide developers in following these best practices, developers are left to implement their own solutions, which often may vary across different applications.

For instance, consider the SQLStatement class. In order to optimize performance of the execution of a statement, the statement must first be prepared (i.e. compiled), which optimizes the statement by the runtime prior to execution. Once a statement is prepared, if the text property does not change, subsequent executions of the statement will execute faster. In order to facilitate this particular optimization developers must first be aware of this best practice, then determine the appropriate way to implement a solution in order to take advantage of the advocated practice. A simple way to facilitate this is to define separate SQLStatement instances for each unique statement which is to be executed more than once, as is suggested by Adobe, and assume the text property is not to be assigned a new value. You could take this a step further as well and define a sub class of SQLStatement which enforces the text property is only assigned a value once, thus ensuring the optimization has been set. The AIR SQL Framework provides such facilities.

The AIR SQL Framework is a simple, reusable framework which facilitates advocated best practices when working with the SQL API in AIR.

At the foundation of the AIR SQL Framework sits the following packages:

• com.ericfeminella.sql The sql package contains a PreparedStatement class for enforcing a SQLStatement instance to only have a text value assigned during instantiation. In addition the sql package contains an ISQLStatementCache interface which can be used to indicate an implementing class is to serve as a repository of reusable PreparedStatement instances.
• com.ericfeminella.sql.dao The DAO package provides abstractions for both synchronous and asynchronous SQL DAO implementations.
• com.ericfeminella.sql.utils The utils package provides helper classes for substituting statement parameters and retrieving shared SQLConnection instances

This distribution of the AIR SQL Framework should be considered an alpha release as there are some additional features which I am planning to implement, namely, the addition of support for named parameter substitutions in the SQLStatementHelper class.

I have provided an example project which demonstrates a simple AIR application built utilizing the AIR SQL Framework, along with the source, binary and documentation.

AIRSQL 0.9.1

Class annotations, also known as metadata in Flex, are extremely valuable as they allow developers to provide additional information about classes, properties and methods which may not be appropriate to convey through implementation details such as Marker interfaces or some other means. An annotation can be viewed as a comment of sorts that provides a facility which can be utilized to convey the intent of a class, property or method, however unlike comments annotations are compiled into byte code with the class, thus allowing inspection at runtime via object introspection / reflection. Annotations do not directly affect code semantics themselves, however they can be inspected at runtime which in turn may affect the semantics of the running application.

Annotations are also very useful for providing pre-compiler instructions for generating boilerplate code. Although custom annotations can not be used in this way directly in Flex, this usage can be found throughout the Flex Framework. A perfect example of how the Flex framework uses annotations to generate boiler plate code is the [Bindable] meta-data tag, which itself is an annotation as are all meta-data tags in Flex. When a class or property is defined as [Bindable] the pre-compiler in turn reads this attribute and generates the code which facilitates actual data binding; i.e. PropertyChangeEvent, IEventDispatcher etc.

In order to use custom annotations in Flex you first need to instruct the compiler to keep Actionscript 3 metadata. This is achieved by using the keep-as3-metadata compiler argument. An example of setting two custom metadata attributes named “Foo” and “Bar” in the Flex IDE under project > compiler options is as follows.

Additionally annotations can be specified in a flex configuration file as follows:

When you create custom metadata in Actionscript you do so by first declaring the name of the annotation followed by arbitrary properties specified as name/value pairs. For example, you are most likely familiar with the [Event] metadata tag in Flex. The name of the annotation is “Event” and the valid properties for the annotation are “name” and “type”, as can be seen below:

Likewise you create your own custom metadata following the same format. The example which follows defines a custom metadata attribute utilized for annotating a class with version information. The name of the annotation is “Version”, which contains three properties; major, minor and revision.

Accessing custom annotations in Flex is accomplished via the flash.utils reflection APIs; describeType, getQualifiedClassName and getDefinitionByName.

To help simplify the process of accessing custom annotations in Flex I have developed a simple API: MetadataUtils which is an all static class that provides utility operations from which class annotations can be located and inspected, and Metadata which provides a strongly typed implementation of a metadata entry.

As you begin experimenting with your own custom annotations you will quickly find that there are numerous applications where they can be utilized, the most significant of which (IMHO) is to help facilitate IoC / DI solutions. It would be great if at some point Adobe would provide an APT implementation for mxmlc as part of a future release of Flex.

This week Adobe announced that Cairngorm has been moved to from Labs to opensource.adobe.com.

So what does this mean for you, as a developer, building RIAs targeting the Adobe Flex platform on top of Cairngorm?

It means a lot.

The most significant being that Cairngorm now has a formal community based initiative. This in itself facilitates positive growth as it encourages community feedback and collaboration. It allows the community to have an open podium for discussion, collaboration and most important, knowledge sharing.

So how can you contribute? To begin, start by signing up as a member and sharing your thoughts and experiences. Get involved; engage in conversations with the rest of the community. Take a look under the hood; get to know Cairngorm internals (if you don’t already).

I have a lot of confidence in the future of Cairngorm and I think we can all expect good things to come.