关于openlayers:ol事件类型

本文次要学习 openlayers 的 Event 模块相干源码

Openlayers 依据 W3C DOM Level 2 Event 接口简化实现了本人的事件类, 它只提供了 type 和target属性以及 preventDefault 和stopPropagation办法。

class BaseEvent {
  /**
   * @param {string} type Type.
   */
  constructor(type) {
    /**
     * @type {boolean}
     */
    this.propagationStopped;

    /**
     * @type {boolean}
     */
    this.defaultPrevented;

    /**
     * The event type.
     * @type {string}
     * @api
     */
    this.type = type;

    /**
     * The event target.
     * @type {Object}
     * @api
     */
    this.target = null;
  }

  /**
   * Prevent default. This means that no emulated `click`, `singleclick` or `doubleclick` events
   * will be fired.
   * @api
   */
  preventDefault() {this.defaultPrevented = true;}

  /**
   * Stop event propagation.
   * @api
   */
  stopPropagation() {this.propagationStopped = true;}
}

EventType对象保留了所有触发地图事件的事件名称。

/**
 * @enum {string}
 * @const
 */
export default {
  /**
   * Generic change event. Triggered when the revision counter is increased.
   * @event module:ol/events/Event~BaseEvent#change
   * @api
   */
  CHANGE: 'change',

  /**
   * Generic error event. Triggered when an error occurs.
   * @event module:ol/events/Event~BaseEvent#error
   * @api
   */
  ERROR: 'error',

  BLUR: 'blur',
  CLEAR: 'clear',
  CONTEXTMENU: 'contextmenu',
  CLICK: 'click',
  DBLCLICK: 'dblclick',
  DRAGENTER: 'dragenter',
  DRAGOVER: 'dragover',
  DROP: 'drop',
  FOCUS: 'focus',
  KEYDOWN: 'keydown',
  KEYPRESS: 'keypress',
  LOAD: 'load',
  RESIZE: 'resize',
  TOUCHMOVE: 'touchmove',
  WHEEL: 'wheel',
};

KeyCode对象只记录了上下左右键盘方向键的 keycode，便于事件监听。

export default {
  LEFT: 37,
  UP: 38,
  RIGHT: 39,
  DOWN: 40,
};