Fix #304

iron-list.html

@@ -1453,9 +1453,11 @@
       if (typeof idx !== 'number' || idx < 0 || idx > this.items.length - 1) {
         return;
       }
-
       Polymer.dom.flush();
-
+      // Items should have been rendered prior scrolling to an index.
+      if (!this._itemsRendered) {
+        return;
+      }
       idx = Math.min(Math.max(idx, 0), this._virtualCount-1);
       // update the virtual start only when needed
       if (!this._isIndexRendered(idx) || idx >= this._maxVirtualStart) {
@@ -1467,16 +1469,13 @@
       this._assignModels();
       // measure the new sizes
       this._updateMetrics();
-
       // estimate new physical offset
-      var estPhysicalTop = Math.floor(this._virtualStart / this._itemsPerRow)  * this._physicalAverage;
-      this._physicalTop = estPhysicalTop;
+      this._physicalTop = Math.floor(this._virtualStart / this._itemsPerRow)  * this._physicalAverage;
 
       var currentTopItem = this._physicalStart;
       var currentVirtualItem = this._virtualStart;
       var targetOffsetTop = 0;
       var hiddenContentSize = this._hiddenContentSize;
-
       // scroll to the item as much as we can
       while (currentVirtualItem < idx && targetOffsetTop <= hiddenContentSize) {
         targetOffsetTop = targetOffsetTop + this._getPhysicalSizeIncrement(currentTopItem);

test/basic.html

@@ -150,6 +150,15 @@
       }, 100);
     });
 
+    test('scroll to index while not attached', function() {
+      var tmpList = document.createElement('iron-list');
+      Polymer.dom(tmpList).appendChild(document.createElement('template'));
+      tmpList.items = buildDataSet(100);
+      assert.equal(tmpList._virtualStart, 0);
+      tmpList.scrollToIndex(50);
+      assert.equal(tmpList._virtualStart, 0);
+    });
+
     test('scroll to item', function(done) {
       list.items = buildDataSet(100);