上一篇博客,我们讲解了SimpleCommand类,接下来我们看一下与SimpleCommand类很相似的MacroCommand类。
MacroCommand类和SimpleCommand类一样,都继承Notifier类(通知者),都可以发送消息。
/* subclass Notifier */ MacroCommand.prototype= new Notifier; MacroCommand.prototype.constructor= MacroCommand;
MacroCommand类比SimpleCommand类多了一个subCommands属性。它是干嘛用的呢?其实,通过类名我们就可以看出MacroCommand类和SimpleCommand类的异同。"SimpleCommand"顾名思义可以理解为”简单的命令,"MacroCommand"可以理解为"巨大的、大量的命令".subCommands是一个数组,它里面存放者多个SimpleCommand类和MacroCommand类(我们把SimpleCommand类和MacroCommand类统称为命令类),在MacroCommand对象接收到消息时,他就会依次调用subCommands里面所有命令的execute()方法(执行命令)。
MacroCommand类和SimpleCommand类一样,都有一个execute()方法(执行命令),但是MacroCommand类的execute()方法比SimpleCommand类的execute()要复杂很多:
/** * Execute this MacroCommands *SubCommands* * * The *SubCommand*s will be called in First In / First Out (FIFO) order * @param {puremvc.Notification} note * The Notification object to be passed to each *SubCommand* */ MacroCommand.prototype.execute= function(note) { // SIC- TODO optimize while(this.subCommands.length > 0) { var ref= this.subCommands.shift(); var cmd= new ref; cmd.initializeNotifier(this.multitonKey); cmd.execute(note); } };
MacroCommand类有一个addSubCommand()方法,用来往subCommands数组里面添加命令类。
/** * @protected * Add a *SubCommand* * The *SubCommand*s will be called in First In / First Out (FIFO) order * @param {Function} commandClassRef * A reference to a subclassed SimpleCommand or MacroCommand constructor */ MacroCommand.prototype.addSubCommand= function(commandClassRef) { this.subCommands.push(commandClassRef); };
我们再看看MacroCommand类的构造函数:
/* * If your subclass does define a constructor, be sure to call "super" like so * * function MyMacroCommand () * { * MacroCommand.call(this); * }; * @constructor */ function MacroCommand() { this.subCommands= []; this.initializeMacroCommand(); };
在MacCommand类的构造函数中,先对subCommands属性进行了初始化,然后调用了initializeMacroCommand()方法。【我们注意注释,可以知道我们继承MacCommand类的,需要在自雷的构造函数中调用MacroCommand的构造函数(MacroComand.call(this)】。
我们看看initializeMacroCommand()方法:
MacroCommand.prototype.initializeMacroCommand= function() {}
initializeMacroCommand类,主要是MacroCommand对象的初始化,在继承MacroCommand的子类中我们需要重写这个方法,源码中有这么一段注释:
* In your subclass, override this method to * initialize the MacroCommand's *SubCommand* * list with command class references like * this: * * // Initialize MyMacroCommand * MyMacroCommand.prototype.initializeMacroCommand= function () * { * this.addSubCommand( com.me.myapp.controller.FirstCommand ); * this.addSubCommand( com.me.myapp.controller.SecondCommand ); * this.addSubCommand( com.me.myapp.controller.ThirdCommand ); * }; * * Note that *SubCommand*s may be any command implementor, * MacroCommands or SimpleCommands are both acceptable.
其实,initializeMacroCommand类其实就是往subCommands数组中添加命令类(可以是SimpleCommand类也可以是MacroCommand类,记住添加的是类名,不是类的实例化对象,MacroCommand对象接收到消息后,会在execute()方法中实例化这些命令类)。
在实际开发过程中,我们需要写一些复杂的逻辑处理单元(Command类),这写逻辑处理类要么继承SimpleCommand,要么继承MacroCommand类,哪什么时候继承MacroCommand类,什么时候继承SimpleCommand类,需要看我们逻辑的复杂度,如果一个逻辑单元可以拆分为多个子逻辑单元,那我们可以继承MacroCommand类,如果一个逻辑单元就可以处理,那我们只需要继承SimpleCommand类。
关于,SimleCommand类和MacroCommand类的不同,源码中有这么一段注释:
* Unlike {@link puremvc.SimpleCommand SimpleCommand}, * your subclass should not override #execute but instead, should * override the #initializeMacroCommand method, calling #addSubCommand once for * each *SubCommand* to be executed. *
上面的注释说的很清楚,就是继承MacroCommand类的子类需要重写initializeMacroCommand方法,不需要重写execute方法,继承SimpleCommand类的子类需要重写execute方法。
最后,附上MacroCommand类的思维导图: