openlayers源码分析（2）

Feature

Feature的父类是BaseObject，先从构造函数开始

构造函数参数可以是一个Geometry对象或者是一个对象包含属性，但是这个对象必须有个geometry属性，而且值必须是Geometry类型。构造函数前面主要是对私有变量初始化。

/**
   * @param {import("./geom/Geometry.js").default|Object=} opt_geometryOrProperties
   *     You may pass a Geometry object directly, or an object literal containing
   *     properties. If you pass an object literal, you may include a Geometry
   *     associated with a `geometry` key.
   */
  constructor(opt_geometryOrProperties) {

    super();

    /**
     * @private
     * @type {number|string|undefined}
     */
    this.id_ = undefined;

    /**
     * @type {string}
     * @private
     */
    this.geometryName_ = 'geometry';

    /**
     * User provided style.
     * @private
     * @type {import("./style/Style.js").StyleLike}
     */
    this.style_ = null;

    /**
     * @private
     * @type {import("./style/Style.js").StyleFunction|undefined}
     */
    this.styleFunction_ = undefined;

    /**
     * @private
     * @type {?import("./events.js").EventsKey}
     */
    this.geometryChangeKey_ = null;

    listen(
      this, getChangeEventType(this.geometryName_),
      this.handleGeometryChanged_, this);

    if (opt_geometryOrProperties) {
      if (typeof /** @type {?} */ (opt_geometryOrProperties).getSimplifiedGeometry === 'function') {
        const geometry = /** @type {import("./geom/Geometry.js").default} */ (opt_geometryOrProperties);
        this.setGeometry(geometry);
      } else {
        /** @type {Object} */
        const properties = opt_geometryOrProperties;
        this.setProperties(properties);
      }
    }
  }

listen函数 主要做了一件事，就是绑定handleGeometryChanged_,并绑定geometryChangeKey_为typeCHANGE的事件监听对象

 /**
   * @private
   */
  handleGeometryChanged_() {
    if (this.geometryChangeKey_) {
      unlistenByKey(this.geometryChangeKey_);
      this.geometryChangeKey_ = null;
    }
    const geometry = this.getGeometry();
    if (geometry) {
      this.geometryChangeKey_ = listen(geometry,
        EventType.CHANGE, this.handleGeometryChange_, this);
    }
    this.changed();
  }

clone方法

不仅深拷贝feature对象，也拷贝geometry对象

  /**
   * Clone this feature. If the original feature has a geometry it
   * is also cloned. The feature id is not set in the clone.
   * @return {Feature} The clone.
   * @api
   */
  clone() {
    const clone = new Feature(this.getProperties());
    clone.setGeometryName(this.getGeometryName());
    const geometry = this.getGeometry();
    if (geometry) {
      clone.setGeometry(geometry.clone());
    }
    const style = this.getStyle();
    if (style) {
      clone.setStyle(style);
    }
    return clone;
  }

getId

  /**
   * Get the feature identifier.  This is a stable identifier for the feature and
   * is either set when reading data from a remote source or set explicitly by
   * calling {@link module:ol/Feature~Feature#setId}.
   * @return {number|string|undefined} Id.
   * @api
   */
  getId() {
    return this.id_;
  }

getGeometryName

  /**
   * Get the name of the feature's default geometry.  By default, the default
   * geometry is named `geometry`.
   * @return {string} Get the property name associated with the default geometry
   *     for this feature.
   * @api
   */
  getGeometryName() {
    return this.geometryName_;
  }

getStyle

  /**
   * Get the feature's style. Will return what was provided to the
   * {@link module:ol/Feature~Feature#setStyle} method.
   * @return {import("./style/Style.js").StyleLike} The feature style.
   * @api
   */
  getStyle() {
    return this.style_;
  }

changed()

  /**
   * Increases the revision counter and dispatches a 'change' event.
   * @api
   */
  changed() {
    ++this.revision_;
    this.dispatchEvent(EventType.CHANGE);
  }

dispatchEvent

  /**
   * Dispatches an event and calls all listeners listening for events
   * of this type. The event parameter can either be a string or an
   * Object with a `type` property.
   *
   * @param {{type: string,
   *     target: (EventTargetLike|undefined),
   *     propagationStopped: (boolean|undefined)}|
   *     import("./Event.js").default|string} event Event object.
   * @return {boolean|undefined} `false` if anyone called preventDefault on the
   *     event object or if any of the listeners returned false.
   * @api
   */
  dispatchEvent(event) {
    const evt = typeof event === 'string' ? new Event(event) : event;
    const type = evt.type;
    evt.target = this;
    const listeners = this.listeners_[type];
    let propagate;
    if (listeners) {
      if (!(type in this.dispatching_)) {
        this.dispatching_[type] = 0;
        this.pendingRemovals_[type] = 0;
      }
      ++this.dispatching_[type];
      for (let i = 0, ii = listeners.length; i < ii; ++i) {
        if (listeners[i].call(this, evt) === false || evt.propagationStopped) {
          propagate = false;
          break;
        }
      }
      --this.dispatching_[type];
      if (this.dispatching_[type] === 0) {
        let pendingRemovals = this.pendingRemovals_[type];
        delete this.pendingRemovals_[type];
        while (pendingRemovals--) {
          this.removeEventListener(type, VOID);
        }
        delete this.dispatching_[type];
      }
      return propagate;
    }
  }

extent

Corner

/**
 * @module ol/extent/Corner
 */

/**
 * Extent corner.
 * @enum {string}
 */
export default {
  BOTTOM_LEFT: 'bottom-left',
  BOTTOM_RIGHT: 'bottom-right',
  TOP_LEFT: 'top-left',
  TOP_RIGHT: 'top-right'
};

Relationship

/**
 * @module ol/extent/Relationship
 */

/**
 * Relationship to an extent.
 * @enum {number}
 */
export default {
  UNKNOWN: 0,
  INTERSECTING: 1,
  ABOVE: 2,
  RIGHT: 4,
  BELOW: 8,
  LEFT: 16
};