backbone 学习之View

View，包含两部分的职责View和Controller.当model更改的时候 view也会相应的跟着更改，同理view更改的时候model也更改，有点MVVM的感觉

直接看源码：

// Backbone.View
  // -------------

  // Backbone Views are almost more convention than they are actual code. A View
  // is simply a JavaScript object that represents a logical chunk of UI in the
  // DOM. This might be a single item, an entire list, a sidebar or panel, or
  // even the surrounding frame which wraps your whole app. Defining a chunk of
  // UI as a **View** allows you to define your DOM events declaratively, without
  // having to worry about render order ... and makes it easy for the view to
  // react to specific changes in the state of your models.

  // Creating a Backbone.View creates its initial element outside of the DOM,
  // if an existing element is not provided...
  var View = Backbone.View = function(options) {
    this.cid = _.uniqueId('view');
    this._configure(options || {});
    this._ensureElement(); // 确保el
    this.initialize.apply(this, arguments);
    this.delegateEvents(); // 绑定事件
  };

  // Cached regex to split keys for `delegate`.
  var delegateEventSplitter = /^(\S+)\s*(.*)$/;

  // List of view options to be merged as properties.
  // view中的关键属性
  var viewOptions = ['model', 'collection', 'el', 'id', 'attributes', 'className', 'tagName', 'events'];

  // Set up all inheritable **Backbone.View** properties and methods.
  _.extend(View.prototype, Events, {

    // The default `tagName` of a View's element is `"div"`.
    // view 的tagName 在没有设置el的时候，默认view的内容的容器就是div
    tagName: 'div',

    // jQuery delegate for element lookup, scoped to DOM elements within the
    // current view. This should be prefered to global lookups where possible.
    // 查找元素
    $: function(selector) {
      return this.$el.find(selector);
    },

    // Initialize is an empty function by default. Override it with your own
    // initialization logic.
    initialize: function(){},

    // **render** is the core function that your view should override, in order
    // to populate its element (`this.el`), with the appropriate HTML. The
    // convention is for **render** to always return `this`.
    // 渲染函数 一般需要重写
    render: function() {
      return this;
    },

    // Remove this view by taking the element out of the DOM, and removing any
    // applicable Backbone.Events listeners.
    // 移除元素
    remove: function() {
      this.$el.remove();
      this.stopListening();
      return this;
    },

    // Change the view's element (`this.el` property), including event
    // re-delegation.
    // 设置元素
    setElement: function(element, delegate) {
      if (this.$el) this.undelegateEvents(); // 解绑 释放内存
      this.$el = element instanceof Backbone.$ ? element : Backbone.$(element);
      this.el = this.$el[0];
      if (delegate !== false) this.delegateEvents();
      return this;
    },

    // Set callbacks, where `this.events` is a hash of
    //
    // *{"event selector": "callback"}*
    //
    //     {
    //       'mousedown .title':  'edit',
    //       'click .button':     'save'
    //       'click .open':       function(e) { ... }
    //     }
    //
    // pairs. Callbacks will be bound to the view, with `this` set properly.
    // Uses event delegation for efficiency.
    // Omitting the selector binds the event to `this.el`.
    // This only works for delegate-able events: not `focus`, `blur`, and
    // not `change`, `submit`, and `reset` in Internet Explorer.
    // 根据键值对来绑定事件
    delegateEvents: function(events) {
      if (!(events || (events = _.result(this, 'events')))) return this;
      this.undelegateEvents();
      for (var key in events) {
        var method = events[key];
        if (!_.isFunction(method)) method = this[events[key]];
        if (!method) continue;

        var match = key.match(delegateEventSplitter);
        var eventName = match[1], selector = match[2];
        method = _.bind(method, this);
        eventName += '.delegateEvents' + this.cid;
        if (selector === '') {
          this.$el.on(eventName, method);
        } else {
          this.$el.on(eventName, selector, method);
        }
      }
      return this;
    },

    // Clears all callbacks previously bound to the view with `delegateEvents`.
    // You usually don't need to use this, but may wish to if you have multiple
    // Backbone views attached to the same DOM element.
    // 解绑事件
    undelegateEvents: function() {
      this.$el.off('.delegateEvents' + this.cid);
      return this;
    },

    // Performs the initial configuration of a View with a set of options.
    // Keys with special meaning *(e.g. model, collection, id, className)* are
    // attached directly to the view.  See `viewOptions` for an exhaustive
    // list.
    // 配置options中的viewOptions中的项到this上
    _configure: function(options) {
      if (this.options) options = _.extend({}, _.result(this, 'options'), options);
      _.extend(this, _.pick(options, viewOptions)); // 拓展this
      this.options = options;
    },

    // Ensure that the View has a DOM element to render into.
    // If `this.el` is a string, pass it through `$()`, take the first
    // matching element, and re-assign it to `el`. Otherwise, create
    // an element from the `id`, `className` and `tagName` properties.
    // 确保有el $el
    _ensureElement: function() {
      if (!this.el) {
        var attrs = _.extend({}, _.result(this, 'attributes')); // options中的attributes
        if (this.id) attrs.id = _.result(this, 'id'); // id
        if (this.className) attrs['class'] = _.result(this, 'className');
        var $el = Backbone.$('<' + _.result(this, 'tagName') + '>').attr(attrs);
        this.setElement($el, false);
      } else {
        this.setElement(_.result(this, 'el'), false);
      }
    }

  });

欢迎指导、纠错、建议。