richwklein.com

Sometimes when developing Firefox extensions, you need to store information on a per tab basis. I’ve developed some reusable code for doing this. As an added bonus the information is stored using the session store api so it will be restored when a tab is restored. It also listens to the private browsing notifications and clears its state when entering or exiting private browsing mode. This code only works in Firefox 3.5 or greater. It is based on 2 JavaScript objects. The first is a tab controller that will store the actual information. This is the object you will need to modify to suit your own purpose. The other is the tab listener that listens to different DOM events to keep track of the first object.

/*******************************************************************************
 *  Object used to store information on a per tab basis.  This should be passed
 *  into the TabListener as the func argument.
 *
 *  @version 1.0
 ******************************************************************************/
function TabController() {}
TabController.prototype = {

  /**
   * IMPORTANT!!! Add the properties here that you need to keep track of.
   */

  /**
   * Called when a tab is being restored so that we restore the controllers state.
   *
   * @param   data           A string of json data stored in the session store.
   */
  fromString: function TabController_fromString(data) {
    var json = window.JSON.parse(data);
    for (var property in json)
        this[property] = json[property];
  },

  /**
   * Called when a tab is being closed so that we can store the controllers state.
   *
   * @returns                A string of json data stored in the session store.
   */
  toString: function TabController_toString() {
    var json = {};
    for (var property in this)
      json[property] = this[property]
    return window.JSON.stringify(json);
  }
};

/*******************************************************************************
 *  Object used to listen to tab events and keep track of controllers
 *
 *  @param    func           The controller function to instantiate.
 *
 *  @version 1.0
 ******************************************************************************/
function TabListener(func) {
  this.func = func;

  // get the session store
  this.store = Components.classes["@mozilla.org/browser/sessionstore;1"].
               getService(Components.interfaces.nsISessionStore);

  // prefill the controller array
  this.prefill();

  // add session event listeners
  document.addEventListener("SSTabRestoring", this, false);
  document.addEventListener("SSTabClosing", this, false);

  // add tab event listeners
  var container = getBrowser().tabContainer;
  container.addEventListener("TabOpen", this, false);
  container.addEventListener("TabMove", this, false);
  container.addEventListener("TabClose", this, false);
  container.addEventListener("TabSelect", this, false);

  // add the private browsing observer
  var os = Components.classes["@mozilla.org/observer-service;1"].
           getService(Components.interfaces.nsIObserverService);
  os.addObserver(this, "private-browsing", true);
}
TabListener.prototype = {
  func: null,
  store: null,

  /**
   * Array of controllers stored in the same order as tabs.
   */
  _controllers: null,
  get controllers() { return this._controllers; },
  set controllers(val) { this._controllers = val; },

  /**
   * Index of the selected tab.
   */
  _index: null,
  get index() { return this._index; },
  set index(val) { this._index = val; },

  /**
   * Controller for the selected tab.
   */
  get selected() { return this.controllers[this.index]; },

  /**
   * Prefill the array of controllers.
   */
  prefill: function TabListener_prefill() {

    // set the index to the selected tab index
    this.index = getBrowser().selectedTab._tPos;

    // loop through the open tabs and instantiate a controller for each tab.
    controllers = []
    var container = getBrowser().tabContainer;
    for (var i=0; i<container.childNodes.length; i++)
      controllers.append(new this.func());
    this.controllers = controllers;
  },

  /* ::::: nsIDOMEventListener ::::: */
  handleEvent: function urlnavOverlay_handleEvent(event) {
    var index = event.originalTarget._tPos;
    var controller;

    switch (event.type) {

    // tab open - store a new controller in the array
    case "TabOpen":
      this.controllers.splice(index, 0, new this.func());
      break;

    // tab is being restored - restore controller from the session store
    case "SSTabRestoring":
      controller = this.controllers[index];
      var data = this.store.getTabValue(event.originalTarget, "tab-controller");
      if (data != "undefined")
        controller.fromString(data);
      break;

    // user moved the tab - move the controller in the array
    case "TabMove":
      var oldIndex = event.detail;
      this.controllers.splice(index, 0, this.controllers.splice(oldIndex, 1)[0]);
      break;

    // tab is closing - save state to the session store
    case "SSTabClosing":
      controller = this.controllers[index];
      this.store.setTabValue(event.originalTarget, "tab-controller", controller.toString());
      break;

    // tab is closed - remove the controller from the array
    case "TabClose":
      this.controllers.splice(index, 1);
      break;

    // tab is selected - change the stored tab index
    case "TabSelect":
      this.index = index;
      break;

    default:
      return;
    }
  },

  /* ::::: nsIObserver ::::: */
  observe: function urlnavOverlay_observe(subject, topic, data) {

    // make sure it's the private browsing topic
    if (topic != "private-browsing")
      return;

    // reset the controllers
    this.prefill();
  },

  /* ::::: nsISupports ::::: */
  QueryInterface: function TabListener_QI(iid) {
    if (iid.equals(Components.interfaces.nsIDOMEventListener) ||
        iid.equals(Components.interfaces.nsIObserver) ||
        iid.equals(Components.interfaces.nsISupportsWeakReference) ||
        iid.equals(Components.interfaces.nsISupports))
      return this;
    throw Components.results.NS_ERROR_NO_INTERFACE;
  }
}

Here is a version you can download and use for yourself.