From 65a62ad1b402caa43438f9dd406e9c27f64e67cc Mon Sep 17 00:00:00 2001
From: Didier Colens <dcolens@cisco.com>
Date: Sun, 4 Feb 2018 18:12:00 +0100
Subject: [PATCH] fix for #998

---
 source/Grid/Grid.jest.js | 80 ++++++++++++++++++++++++++++++++++++++++
 source/Grid/Grid.js      |  5 ++-
 2 files changed, 84 insertions(+), 1 deletion(-)

diff --git a/source/Grid/Grid.jest.js b/source/Grid/Grid.jest.js
index a71365db1..1000e8aa8 100644
--- a/source/Grid/Grid.jest.js
+++ b/source/Grid/Grid.jest.js
@@ -637,6 +637,86 @@ describe('Grid', () => {
       expect(node.scrollTop).toBe(1920);
     });
 
+    // See issue #998
+    it('call to recomputeGridSize should not reset position to scrollToRow when scrolling forward', () => {
+      const cellRendererCalls = [];
+      function cellRenderer({ columnIndex, key, rowIndex, style }) {
+        cellRendererCalls.push({ columnIndex, rowIndex });
+        return defaultCellRenderer({ columnIndex, key, rowIndex, style });
+      }
+      const props = {
+        cellRenderer,
+        columnWidth: 100,
+        height: 40,
+        rowHeight: 20,
+        scrollToRow: 0,
+        width: 100,
+      };
+
+      const grid = render(getMarkup(props));
+      expect(cellRendererCalls).toEqual([
+        { columnIndex: 0, rowIndex: 0 },
+        { columnIndex: 0, rowIndex: 1 },
+      ]);
+
+      //scroll forward to row 45
+      simulateScroll({ grid, scrollTop: 900 });
+
+      expect(grid.state.scrollDirectionVertical).toEqual(
+        SCROLL_DIRECTION_FORWARD,
+      );
+      cellRendererCalls.splice(0);
+
+      grid.recomputeGridSize({ rowIndex: 45 });
+
+      //grid should still be at row 45
+      expect(cellRendererCalls).toEqual([
+        { columnIndex: 0, rowIndex: 45 },
+        { columnIndex: 0, rowIndex: 46 },
+      ]);
+    });
+    // see #998
+    it('call to recomputeGridSize should not reset position to scrollToRow when scrolling backward', () => {
+      const cellRendererCalls = [];
+      function cellRenderer({ columnIndex, key, rowIndex, style }) {
+        cellRendererCalls.push({ columnIndex, rowIndex });
+        return defaultCellRenderer({ columnIndex, key, rowIndex, style });
+      }
+      const props = {
+        cellRenderer,
+        columnWidth: 100,
+        height: 40,
+        rowHeight: 20,
+        scrollToRow: 99,
+        width: 100,
+      };
+
+      const grid = render(getMarkup(props));
+      expect(cellRendererCalls).toEqual([
+        { columnIndex: 0, rowIndex: 0 },
+        { columnIndex: 0, rowIndex: 1 },
+        { columnIndex: 0, rowIndex: 98 },
+        { columnIndex: 0, rowIndex: 99 },
+      ]);
+
+      //scroll backward to row 45
+      simulateScroll({ grid, scrollTop: 900 });
+
+      expect(grid.state.scrollDirectionVertical).toEqual(
+        SCROLL_DIRECTION_BACKWARD,
+      );
+      cellRendererCalls.splice(0);
+
+      grid.recomputeGridSize({ rowIndex: 45 });
+      
+      //grid should still be at row 45
+      expect(cellRendererCalls).toEqual([
+        { columnIndex: 0, rowIndex: 45 },
+        { columnIndex: 0, rowIndex: 46 },
+      ]);
+    });
+
+
     it('should restore scroll offset for column when row count increases from 0 (and vice versa)', () => {
       const props = {
         columnWidth: 50,
diff --git a/source/Grid/Grid.js b/source/Grid/Grid.js
index 423ea5762..c7b74df54 100644
--- a/source/Grid/Grid.js
+++ b/source/Grid/Grid.js
@@ -481,7 +481,10 @@ export default class Grid extends React.PureComponent<Props, State> {
     // Store this flag to let the next cDU pass know it needs to recompute the scroll offset.
     this._recomputeScrollLeftFlag =
       scrollToColumn >= 0 && columnIndex <= scrollToColumn;
-    this._recomputeScrollTopFlag = scrollToRow >= 0 && rowIndex <= scrollToRow;
+    this._recomputeScrollTopFlag = scrollToRow >= 0 &&
+      (this.state.scrollDirectionVertical === SCROLL_DIRECTION_FORWARD ?
+        rowIndex <= scrollToRow :
+        rowIndex >= scrollToRow);
 
     // Clear cell cache in case we are scrolling;
     // Invalid row heights likely mean invalid cached content as well.