Mention ngx-ui-scroll in README

DynamicVirtualScroll.js

@@ -62,7 +62,7 @@ export function virtualScrollDriver(props, oldState, getRenderedItemHeight)
             if (!lastItemSize)
             {
                 // Some required items in the end are missing
-                return newState;
+                lastItemSize = 0;
             }
             lastItemsHeight += lastItemSize < props.minRowHeight ? props.minRowHeight : lastItemSize;
             lastVisibleItems++;

README.md

@@ -5,12 +5,12 @@ of visible items and skip items that are offscreen. You may also have heard abou
 "buffered render" or "windowed render" - it's the same.
 
 There are plenty of virtual scroll implementations for JS.
-Some of them are part of a larger UI library (ag-grid, ExtJS and so on),
-some of them are more standalone (react-virtualized, react-window, ngx-virtual-scroller, react-dynamic-virtual-list).
+Some of them are part of a larger UI library (ag-grid, ExtJS and so on), some of them are more
+standalone (react-virtualized, react-window, ngx-virtual-scroller, ngx-ui-scroll, react-dynamic-virtual-list).
 
 However, there is a thing that they all miss: dynamic (and unknown apriori) row heights.
 Some implementations allow to set different row heights for items, but you must calculate
-all heights before rendering; some allow dynamic row heights, but have bugs and do not really work;
+all heights before rendering; some allow dynamic row heights, but have bugs and act weird or don't really work;
 others just force you to use fixed row height. Most implementations are also tied to some specific
 UI component or framework and are unusable with other ones.
 

VirtualScrollList.js

@@ -36,10 +36,22 @@ export class VirtualScrollList extends React.Component
 
     setItemRef = []
     itemRefs = []
+    itemRefCount = []
 
     makeRef(i)
     {
-        this.setItemRef[i] = (e) => this.itemRefs[i] = e;
+        this.setItemRef[i] = (e) =>
+        {
+            // If the new row instance is mounted before unmouting the old one,
+            // we get called 2 times in wrong order: first with the new instance,
+            // then with null telling us that the old one is unmounted.
+            // We track reference count to workaround it.
+            this.itemRefCount[i] = (this.itemRefCount[i]||0) + (e ? 1 : -1);
+            if (e || !this.itemRefCount[i])
+            {
+                this.itemRefs[i] = e;
+            }
+        };
     }
 
     renderItems(start, count, is_end)
@@ -63,9 +75,10 @@ export class VirtualScrollList extends React.Component
     render()
     {
         if (this.state.totalItems && this.props.totalItems != this.state.totalItems &&
-            this.state.scrollTimes <= 0)
+            this.state.scrollTimes <= 0 && this.viewport && this.viewport.offsetParent)
         {
-            // Automatically preserve scroll position when item count changes
+            // Automatically preserve scroll position when item count changes...
+            // But only when the list is on-screen! We'll end up with an infinite update loop if it's off-screen.
             this.state.scrollTo = this.getItemScrollPos();
             this.state.scrollTimes = 2;
         }
@@ -86,7 +99,7 @@ export class VirtualScrollList extends React.Component
             onScroll={this.onScroll}>
             {this.props.header}
             {this.state.targetHeight > 0
-                ? <div key="target" style={{position: 'absolute', left: '-5px', width: '1px', height: this.state.targetHeight+'px'}}></div>
+                ? <div key="target" style={{position: 'absolute', top: 0, left: '-5px', width: '1px', height: this.state.targetHeight+'px'}}></div>
                 : null}
             {this.state.topPlaceholderHeight
                 ? <div style={{height: this.state.topPlaceholderHeight+'px'}} key="top"></div>
@@ -111,7 +124,10 @@ export class VirtualScrollList extends React.Component
             const e = ReactDOM.findDOMNode(this.itemRefs[index]);
             if (e)
             {
-                return e.getBoundingClientRect().height;
+                // MSIE sometimes manages to report non-integer element heights for elements of an integer height...
+                // Non-integer element sizes are allowed in getBoundingClientRect, one notable example of them
+                // are collapsed table borders. But we still ignore less than 1/100 of a pixel difference.
+                return Math.round(e.getBoundingClientRect().height*100)/100;
             }
         }
         return 0;
@@ -120,12 +136,17 @@ export class VirtualScrollList extends React.Component
     onScroll = () =>
     {
         this.driver();
+        if (this.props.onScroll)
+        {
+            this.props.onScroll(this.viewport);
+        }
     }
 
     componentDidUpdate = () =>
     {
         let changed = this.driver();
-        if (!changed && this.state.scrollTimes > 0 && this.props.totalItems > 0)
+        if (!changed && this.state.scrollTimes > 0 && this.props.totalItems > 0 &&
+            this.viewport && this.viewport.offsetParent)
         {
             // FIXME: It would be better to find a way to put this logic back into virtual-scroll-driver
             let pos = this.state.scrollTo;
@@ -181,6 +202,11 @@ export class VirtualScrollList extends React.Component
 
     driver = () =>
     {
+        if (!this.viewport || !this.viewport.offsetParent)
+        {
+            // Fool tolerance - do nothing if we are hidden
+            return false;
+        }
         const newState = virtualScrollDriver(
             {
                 totalItems: this.props.totalItems,

package.json

@@ -1,6 +1,6 @@
 {
   "name": "dynamic-virtual-scroll",
-  "version": "1.0.8",
+  "version": "1.0.15",
   "author": {
     "name": "Vitaliy Filippov",
     "email": "vitalif@yourcmc.ru",