In the event that size or cell count decreases for a , remaining cells are no longer remeasured in order to verify the current scroll offset.

bvaughn · bvaughn · commit 08a27f6b1de2 · 2016-09-01T18:14:45.000-07:00
Instead the most recent measurements are used.
This change should positively impact performance but should have no other affect.
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -1,6 +1,11 @@
 Changelog
 ------------
 
+##### 7.22.2
+In the event that size or cell count decreases for a `Grid`, remaining cells are no longer remeasured in order to verify the current scroll offset.
+Instead the most recent measurements are used.
+This change should positively impact performance but should have no other affect.
+
 ##### 7.22.1
 `InfiniteLoader` now better handles `FlexTable` and `VirtualScroll` children by calling `forceUpdateGrid` when defined.
 This prevents rows from being stuck in a visual "loading" state until a user scrolls.
diff --git a/package.json b/package.json
@@ -3,7 +3,7 @@
   "description": "React components for efficiently rendering large, scrollable lists and tabular data",
   "author": "Brian Vaughn <brian.david.vaughn@gmail.com>",
   "user": "bvaughn",
-  "version": "7.22.1",
+  "version": "7.22.2",
   "homepage": "https://github.com/bvaughn/react-virtualized",
   "main": "dist/commonjs/index.js",
   "jsnext:main": "dist/es/index.js",
diff --git a/source/Grid/utils/updateScrollIndexHelper.js b/source/Grid/utils/updateScrollIndexHelper.js
@@ -60,16 +60,11 @@ export default function updateScrollIndexHelper ({
       cellCount < previousCellsCount
     )
   ) {
-    scrollToIndex = cellCount - 1
-
-    const calculatedScrollOffset = cellSizeAndPositionManager.getUpdatedOffsetForIndex({
-      containerSize: size,
-      currentOffset: scrollOffset,
-      targetIndex: scrollToIndex
-    })
-
+    // We need to ensure that the current scroll offset is still within the collection's range.
+    // To do this, we don't need to measure everything; CellMeasurer would perform poorly.
+    // Just check to make sure we're still okay.
     // Only adjust the scroll position if we've scrolled below the last set of rows.
-    if (calculatedScrollOffset < scrollOffset) {
+    if (scrollOffset > cellSizeAndPositionManager.getTotalSize() - size) {
       updateScrollIndexCallback(cellCount - 1)
     }
   }
diff --git a/source/Grid/utils/updateScrollIndexHelper.test.js b/source/Grid/utils/updateScrollIndexHelper.test.js
@@ -30,7 +30,7 @@ describe('updateScrollIndexHelper', () => {
     cellCount = undefined,
     cellSizeAndPositionManager,
     cellSize = 10,
-    previousCellsCount = 100,
+    previousCellsCount = undefined,
     previousCellSize = 10,
     previousScrollToAlignment = 'auto',
     previousScrollToIndex,
@@ -44,6 +44,9 @@ describe('updateScrollIndexHelper', () => {
     cellCount = cellCount === undefined
       ? cellSizeAndPositionManager.getCellCount()
       : cellCount
+    previousCellsCount = previousCellsCount === undefined
+      ? cellCount
+      : previousCellsCount
 
     let updateScrollIndexCallbackCalled = false
 
@@ -123,6 +126,20 @@ describe('updateScrollIndexHelper', () => {
     })).toEqual(true)
   })
 
+  it('should not measure rows if :size or :cellCount have been reduced but only use already measured (or estimated) total size', () => {
+    const cellSizeAndPositionManager = {
+      getCellCount: () => CELL_SIZES.length,
+      getTotalSize: () => 560
+    }
+
+    expect(helper({
+      cellSizeAndPositionManager,
+      previousSize: 100,
+      scrollOffset: 510,
+      size: 50
+    })).toEqual(false)
+  })
+
   it('should not call :updateScrollIndexCallback if there is no :scrollToIndex but :cellCount has been increased', () => {
     expect(helper({
       cellCount: 100,
