MD Settings: Save and restore scroll position in iron-list

chrome/browser/resources/settings/bluetooth_page/bluetooth_device_dialog.js

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 cr.exportPath('settings');
 
 (function() {
 
 var PairingEventType = chrome.bluetoothPrivate.PairingEventType;
 
@@ skipping 14 matching lines @@
 
     /**
      * The ordered list of bluetooth devices.
      * @type {!Array<!chrome.bluetooth.Device>}
      */
     deviceList: {
       type: Array,
       value: /** @return {Array} */ function() {
         return [];
       },
-      observer: 'deviceListChanged_',
+    },
+
+    /**
+     * The ordered list of unpaired bluetooth devices.
+     * @type {!Array<!chrome.bluetooth.Device>}
+     */
+    unpairedDeviceList_: {
+      type: Array,
+      value: /** @return {Array} */ function() {
+        return [];
+      },
     },
 
     /**
      * Reflects the iron-list selecteditem property.
      * @type {!chrome.bluetooth.Device}
      */
-    selectedItem: {
+    selectedItem_: {
       type: Object,
       observer: 'selectedItemChanged_',
     },
   },
 
-  /** @type {boolean} */ itemWasFocused_: false,
+  observers: ['deviceListChanged_(deviceList.*)'],
+
+  /** @type {boolean} */
+  itemWasFocused_: false,
 
   /** @private */
   adapterStateChanged_: function() {
     if (!this.adapterState.powered)
       this.close();
   },
 
   /** @private */
   deviceListChanged_: function() {
+    var devices = this.$.devices;
+    this.saveScroll(devices);
+    this.unpairedDeviceList_ = this.deviceList.filter(function(device) {
+      return !device.paired;
+    });

[Dan Beam, 2017/01/24 06:15:18]

can't we just make this do a diff instead?

iron-list is pretty good at handling change to specific items with the mutation
API (i.e. splice, set, append).  can we just add / remove and potentially keep
in sorted order for consistency?

we used to do something like this in downloads.

     this.updateScrollableContents();
-    if (this.itemWasFocused_ || !this.getUnpaired_().length)
+    this.restoreScroll(devices);
+
+    if (this.itemWasFocused_ || !this.unpairedDeviceList_.length)
       return;
     // If the iron-list is populated with at least one visible item then
     // focus it.
     let item = this.$$('iron-list bluetooth-device-list-item');
     if (item && item.offsetParent != null) {
       item.focus();
       this.itemWasFocused_ = true;
       return;
     }
     // Otherwise try again.
     setTimeout(function() { this.deviceListChanged_(); }.bind(this), 100);
   },
 
   /** @private */
   selectedItemChanged_: function() {
-    if (this.selectedItem)
-      this.fire('device-event', {action: 'connect', device: this.selectedItem});
+    if (!this.selectedItem_)
+      return;
+    this.fire('device-event', {action: 'connect', device: this.selectedItem_});
   },
 
   /**
-   * @return {!Array<!chrome.bluetooth.Device>}
+   * @return {boolean}
    * @private
    */
-  getUnpaired_: function() {
-    return this.deviceList.filter(function(device) {
-      return !device.paired;
-    });
-  },
-
-  /**
-   * @return {boolean} True if deviceList contains any unpaired devices.
-   * @private
-   */
-  haveUnpaired_: function(deviceList) {
-    return this.getUnpaired_().length > 0;
+  haveUnpaired_: function() {
+    return this.unpairedDeviceList_.length > 0;
   },
 };
 
 /** @polymerBehavior */
 settings.BluetoothPairDeviceBehavior = {
   properties: {
     /**
      * Current Pairing device.
      * @type {?chrome.bluetooth.Device|undefined}
      */
@@ skipping 301 matching lines @@
   },
 
   /** @private */
   onDialogCanceled_: function() {
     if (this.dialogId == 'pairDevice')
       this.sendResponse_(chrome.bluetoothPrivate.PairingResponse.CANCEL);
   },
 });
 
 })();