ActionScript 3.0 Design Patterns.pdf - VideoTutorials-bg.com

Client
Figure 7-3. Command pattern class diagram
The client assigns each ConcreteCommand instance to specific triggers in invokers.
Invokers are where the commands are called from. They hold on to the
ConcreteCommand objects and call their execute( ) methods when it’s time to execute
the command. You’ll clearly see how this is implemented in ActionScript 3.0 in the
minimalist application.
Minimalist Example of a Command Pattern
This example implements the command pattern class diagram in Figure 7-3. The
command pattern consists of the command interface, concrete commands that implement
the command interface, invokers that call the execute( ) method in concrete
commands, receivers that implement the behavior required of commands, and clients
that create concrete commands and pass them on to invokers.
Code examples Examples 7-1 through 7-5 show the minimalist implementation of
the command pattern.
The Command Interface
Example 7-1 shows the ICommand class that defines the interface for commands. It
defines a single method called execute( ).
Example 7-1. ICommand.as
The Concrete Command
Invoker
Receiver
action()
package
{
public interface ICommand {
function execute( ):void;
}
}
receiver
Command
execute()
ConcreteCommand
execute()
receiver->action()
Example 7-2 shows the ConcreteCommand class that implements the ICommand interface.
The parameterized constructor takes a Receiver class instance and assigns it to
the receiver property. The execute( ) command is implemented by delegating to the
receiver instance by calling its action( ) method. Note that, because the receiver
Minimalist Example of a Command Pattern | 251