(FFOS Gecko & Gaia) OTA - 重回Gaia层

var detail = evt.detail;

if (detail.type && detail.type === ‘update-available‘) {
  // systemUpdatable是在UpdateManager初始化时new出来的，UpdateManager中只会存在一个SystemUpdatable。
  this.systemUpdatable.size = detail.size;
  this.systemUpdatable.rememberKnownUpdate();
  // 添加到UpdateManager中的updatesQueue队列。
  this.addToUpdatesQueue(this.systemUpdatable);
}

    addToUpdatesQueue: function um_addToUpdatesQueue(updatable) {
      if (this._downloading) {
        return;
      }

      if (updatable.app &&
          updatable.app.installState !== ‘installed‘) {
        return;
      }

      if (updatable.app &&
          this.updatableApps.indexOf(updatable) === -1) {
        return;
      }

      var alreadyThere = this.updatesQueue.some(function lookup(u) {
        return (u.app === updatable.app);
      });
      if (alreadyThere) {
        return;
      }

      this.updatesQueue.push(updatable);

      if (this._notificationTimeout === null) {
        this._notificationTimeout = setTimeout(
          this.displayNotificationAndToaster.bind(this),
          this.NOTIFICATION_BUFFERING_TIMEOUT);
      }
      this.render();
    },

this.downloadButton = document.getElementById(‘updates-download-button‘);
this.downloadButton.onclick = this.requestDownloads.bind(this);

requestDownloads: function um_requestDownloads(evt) {
  evt.preventDefault();
  // 通过DataConnection去下载
  if (evt.target == this.downloadViaDataConnectionButton) {
    this._startedDownloadUsingDataConnection = true;
    this.startDownloads();
  } else {
    this.promptOrDownload();
  }
},

    promptOrDownload: function um_promptOrDownload() {
      var self = this;

      if (self.downloadDialog.dataset.online == ‘false‘) {
        self.showPromptNoConnection();
        return;
      }
      // check wifi
      if (self._wifiAvailable()) {
        self._startedDownloadUsingDataConnection = false;
        self.startDownloads();
        return;
      }
    ……
    }

    startDownloads: function um_startDownloads() {
      this.downloadViaDataConnectionDialog.classList.remove(‘visible‘);
      this._closeDownloadDialog();
      Service.request(‘UtilityTray:show‘);

      var checkValues = {};
      var dialog = this.downloadDialogList;
      var checkboxes = dialog.querySelectorAll(‘input[type="checkbox"]‘);
      for (var i = 0; i < checkboxes.length; i++) {
        var checkbox = checkboxes[i];
        checkValues[checkbox.dataset.position] = checkbox.checked;
      }

      // 遍历updatesQueue
      this.updatesQueue.forEach(function(updatable, index) {
        // The user opted out of the download
        if (updatable.app && !checkValues[index]) {
          return;
        }

        updatable.download();
      });

      this._downloadedBytes = 0;
      this.render();
    },

SystemUpdatable.prototype.download = function() {
  if (this.downloading) {
    return;
  }

  this.downloading = true;
  this.paused = false;
  UpdateManager.addToDownloadsQueue(this);
  this.progress = 0;
  this._dispatchEvent(‘update-available-result‘, ‘download‘);
};

    addToDownloadsQueue: function um_addToDownloadsQueue(updatable) {
      if (updatable.app &&
          this.updatableApps.indexOf(updatable) === -1) {
        return;
      }

      var alreadyThere = this.downloadsQueue.some(function lookup(u) {
        return (u.app === updatable.app);
      });
      if (alreadyThere) {
        return;
      }

      this.downloadsQueue.push(updatable);

      if (this.downloadsQueue.length === 1) {
        this._downloading = true;
        Service.request(‘incDownloads‘);
        this._wifiLock = navigator.requestWakeLock(‘wifi‘);

        this.displayNotificationIfHidden();
        this.render();
      }
    },