Modules

Estou estudando sobre módulos (Flex 3 Developer Guide) e fiz um resumo dos tópicos que achei importantes para melhor fixação e abaixo estou disponibilizando este resumo.

About modules

Modules are SWF files that can be loaded and unloaded by an application. They cannot be run independently of an application, but any number of applications can share the modules. The main application, can dynamically load other modules that it requires, when it needs them.

Benefits of modules

• Smaller initial download size of the SWF file.
• Shorter load time due to smaller SWF file size.
• Better encapsulation of related aspects of an application.

A module is a special type of dynamically loadable SWF that contains an IFlexModuleFactory class factory. This allows an application to load code at run time and create class instances without requiring that the class implementations be linked into the main application. Modules are similar to Runtime Shared Libraries (RSLs) in that they separate code from an application into separately loaded SWF files. Modules are much more flexible than RSLs because modules can be loaded and unloaded at run time and compiled without the application.

Creating ActionScript-based modules

If your module does not include any framework code, you can create a class that extends ModuleBase. If you use the ModuleBase class, your module will typically be smaller than if you use a module based on the Module class because it does not have any framework class dependencies.

Reducing module size

Module size varies based on the components and classes that are used in the module. By default, a module includes all framework code that its components depend on, which can cause modules to be large by linking classes that overlap with the application’s classes.

To reduce the size of the modules, you can optimize the module by instructing it to externalize classes that are included by the application. The result is that the module includes only the classes it requires, while the framework code and other dependencies are included in the application.

To externalize framework classes with the command-line compiler, you generate a linker report from the application that loads the modules. You then use this report as input to the module’s load-externs compiler option. The compiler externalizes all classes from the module for which the application contains definitions. This process is also necessary if your modules are in a separate project from your main application in Flex Builder.

1. Generate the linker report and compile the application:
mxmlc -link-report=report.xml MyApplication.mxml

2. Compile the module and pass the linker report to the load-externs option:

mxmlc -load-externs=report.xml MyModule.mxml

Note: If you externalize the module’s dependencies by using the load-externs or optimize option, your module might not be compatible with future versions of Adobe Flex.

Note: At Flash Builder this process can be performed in Project > Properties > Flex Modules.

ModuleManager and ModuleLoader

The ModuleManager manages the set of loaded modules, which are treated as a map of Singletons that are indexed by the module URL. The ModuleLoader class is a thin layer on top of the ModuleManager API that is intended to act similarly to the mx.controls.SWFLoader class for modules that only define a single visual UIComponent. The ModuleLoader class is the easiest class to use when implementing a module-based architecture, but the ModuleManager provides greater control over the modules.

When you load a module, Flex ensures that there is only one copy of a module loaded, no matter how many times you call the loadModule() method for that module.

Using the ModuleLoader class to load modules

Setting the target URL of a ModuleLoader object triggers a call to the loadModule() method. This occurs when you first create a ModuleLoader object with the url property set. It also occurs if you change the value of that property.

If you set the value of the url property to an empty string (""), the ModuleLoader object unloads the current module.

Using the ModuleManager class to load modules

To use the ModuleManager to load a module in ActionScript, you first get a reference to the module’s IModuleInfo interface by using the ModuleManager getModule() method. You then call the interface’s load() method.

Finally, you use the factory property of the interface to call the create() method and cast the return value as the module’s class.

import mx.events.ModuleEvent;
import mx.modules.ModuleManager;
import mx.modules.IModuleInfo;
public var info:IModuleInfo;

private function initApp():void {

info = ModuleManager.getModule("ColumnChartModule.swf");
info.addEventListener(ModuleEvent.READY, modEventHandler);
// Load the module into memory. Calling load() makes the
// IFlexModuleFactory available. You can then get an
// instance of the class using the factory's create() method.
info.load();

}

private function modEventHandler(e:ModuleEvent):void {

// Add an instance of the module's class to the display list.
vb1.addChild(info.factory.create() as ColumnChartModule);

}

You do not need to call the unload() method when adding and removing modules using the IModuleInfo class. You just need to set the IModuleInfo instance to null.

Module domains

By default, a module is loaded into a sibling domain of the current application domain. You can specify a different application domain by using the applicationDomain property of the ModuleLoader class. Because a module is loaded into a child domain, it owns class definitions that are not in the main application’s domain. For example, the first module to load the PopUpManager class becomes the owner of the PopUpManager class for the entire application because it registers the manager with the SingletonManager. If another module later tries to use the PopUpManager, Adobe ® Flash® Player throws an exception. The solution is to ensure that managers such as PopUpManager and DragManager and any other shared services are defined by the main application (This technique also applies to components). Typically, this is done by adding the following to a script block:

import mx.managers.PopUpManager;
import mx.managers.DragManager;
private var popUpManager:PopUpManager;
private var dragManager:DragManager;

Because a Flex module must be in the same security domain as the application (SWF) that loads it, when you’re using modules in an AIR application any module SWF must be located in the same directory as the main application SWF or one of its subdirectories, which ensures that like the main application SWF, the module SWF is in the AIR application security sandbox.

By default, modules do not share the main application’s StyleManager, however. They have their own instances of the IStyleManager2 class. As a result, modules can define their own styles. For example, style properties set on a Button control in one module are not applied to the Button control in another module or to the main application.

See also:
Gerenciamento de memória e tamanho dos arquivos em grandes aplicativos utilizando o Modules do Flex 2.0.1
Module unload doesn't competely unload a module (SDK-12025)