# ComponentMgr.js

    /**
     * @class Ext.ComponentMgr
     * <p>Provides a registry of all Components (instances of {@link Ext.Component} or any subclass
     * thereof) on a page so that they can be easily accessed by component id (see {@link #get}, or
     * the convenience method {@link Ext#getCmp Ext.getCmp}).</p>
     * <p>This object also provides a registry of available Component <i>classes</i>
     * indexed by a mnemonic code known as the Component's {@link Ext.Component#xtype xtype}.
     * The <tt>xtype</tt> provides a way to avoid instantiating child Components
     * when creating a full, nested config object for a complete Ext page.</p>
     * <p>A child Component may be specified simply as a <i>config object</i>
     * as long as the correct xtype is specified so that if and when the Component
     * needs rendering, the correct type can be looked up for lazy instantiation.</p>
     * <p>For a list of all available xtypes, see {@link Ext.Component}.</p>
     * @singleton
     */
    Ext.ComponentMgr = function(){
        var all = new Ext.util.MixedCollection();
        var types = {};

        return {
            /**
             * Registers a component.
             * @param {Ext.Component} c The component
             */
            register : function(c){
                all.add(c);
            },

            /**
             * Unregisters a component.
             * @param {Ext.Component} c The component
             */
            unregister : function(c){
                all.remove(c);
            },

            /**
             * Returns a component by id
             * @param {String} id The component id
             * @return Ext.Component
             */
            get : function(id){
                return all.get(id);
            },

            /**
             * Registers a function that will be called when a specified component is added to ComponentMgr
             * @param {String} id The component id
             * @param {Function} fn The callback function
             * @param {Object} scope The scope of the callback
             */
            onAvailable : function(id, fn, scope){
                all.on("add", function(index, o){
                    if(o.id == id){
                        fn.call(scope || o, o);
                        all.un("add", fn, scope);
                    }
                });
            },

            /**
             * The MixedCollection used internally for the component cache. An example usage may be subscribing to
             * events on the MixedCollection to monitor addition or removal.  Read-only.
             * @type {MixedCollection}
             */
            all : all,

            /**
             * <p>Registers a new Component constructor, keyed by a new
             * {@link Ext.Component#xtype}.</p>
             * <p>Use this method to register new subclasses of {@link Ext.Component} so
             * that lazy instantiation may be used when specifying child Components.
             * see {@link Ext.Container#items}</p>
             * @param {String} xtype The mnemonic string by which the Component class
             * may be looked up.
             * @param {Constructor} cls The new Component class.
             */
            registerType : function(xtype, cls){
                types[xtype] = cls;
                cls.xtype = xtype;
            },

            /**
             * Creates a new Component from the specified config object using the
             * config object's {@link Ext.component#xtype xtype} to determine the class to instantiate.
             * @param {Object} config A configuration object for the Component you wish to create.
             * @param {Constructor} defaultType The constructor to provide the default Component type if
             * the config object does not contain an xtype. (Optional if the config contains an xtype).
             * @return {Ext.Component} The newly instantiated Component.
             */
            create : function(config, defaultType){
                return new types[config.xtype || defaultType](config);
            }
        };
    }();

    /**
     * Shorthand for {@link Ext.ComponentMgr#registerType}
     * @param {String} xtype The mnemonic string by which the Component class
     * may be looked up.
     * @param {Constructor} cls The new Component class.
     * @member Ext
     * @method reg
     */
    Ext.reg = Ext.ComponentMgr.registerType; // this will be called a lot internally, shorthand to keep the bytes down

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