[DataGrid] Fix reset of virtualPage

packages/grid/_modules_/grid/components/containers/GridDataContainer.tsx

@@ -1,6 +1,10 @@
 import * as React from 'react';
 import { GRID_DATA_CONTAINER_CSS_CLASS } from '../../constants/cssClassesConstants';
-import { useGridState } from '../../hooks/features/core/useGridState';
+import { useGridSelector } from '../../hooks/features/core/useGridSelector';
+import {
+  gridDataContainerSizesSelector,
+  gridScrollBarSizeSelector,
+} from '../../hooks/root/gridContainerSizesSelector';
 import { classnames } from '../../utils';
 import { GridApiContext } from '../GridApiContext';
 
@@ -9,14 +13,15 @@ type GridDataContainerProps = React.HTMLAttributes<HTMLDivElement>;
 export function GridDataContainer(props: GridDataContainerProps) {
   const { className, ...other } = props;
   const apiRef = React.useContext(GridApiContext);
-  const [gridState] = useGridState(apiRef!);
+  const dataContainerSizes = useGridSelector(apiRef!, gridDataContainerSizesSelector);
+  const scrollBar = useGridSelector(apiRef!, gridScrollBarSizeSelector);
 
   const style: any = {
-    minWidth: gridState.containerSizes?.dataContainerSizes?.width,
+    minWidth: dataContainerSizes?.width,
   };
 
-  if (gridState.scrollBar.hasScrollY) {
-    style.minHeight = gridState.containerSizes?.dataContainerSizes?.height!;
+  if (scrollBar.hasScrollY) {
+    style.minHeight = dataContainerSizes?.height!;
   }
 
   return (

packages/grid/_modules_/grid/hooks/features/virtualization/useGridVirtualRows.ts

@@ -156,6 +156,11 @@ export const useGridVirtualRows = (
         logger.debug(`Changing page from ${page} to ${nextPage}`);
         requireRerender = true;
       } else {
+        if (!containerProps.isVirtualized && page > 0) {
+          logger.debug(`Virtualization disabled, setting virtualPage to 0`);
+          setRenderingState({ virtualPage: 0 });
+        }
+
         scrollTo(scrollParams);
       }
       setRenderingState({

packages/grid/_modules_/grid/hooks/root/gridContainerSizesSelector.ts

@@ -1,11 +1,19 @@
 import { createSelector } from 'reselect';
+import { ElementSize } from '../../models/elementSize';
 import { GridContainerProps } from '../../models/gridContainerProps';
 import { GridState } from '../features/core/gridState';
 
 export const gridContainerSizesSelector = (state: GridState) => state.containerSizes;
 export const gridViewportSizesSelector = (state: GridState) => state.viewportSizes;
 export const gridScrollBarSizeSelector = (state: GridState) => state.scrollBar;
 
+export const gridDataContainerSizesSelector = createSelector<
+  GridState,
+  GridContainerProps | null,
+  ElementSize | null
+>(gridContainerSizesSelector, (containerSizes) =>
+  containerSizes == null ? null : containerSizes.dataContainerSizes,
+);
 export const gridDataContainerHeightSelector = createSelector<
   GridState,
   GridContainerProps | null,

packages/grid/x-grid/src/tests/rows.XGrid.test.tsx

@@ -358,6 +358,34 @@ describe('<XGrid /> - Rows', () => {
       expect(isVirtualized).to.equal(false);
     });
 
+    it('should set the virtual page to 0 when resetting rows to a non virtualized length', () => {
+      const { setProps } = render(<TestCaseVirtualization nbRows={996} hideFooter height={600} />);
+
+      const gridWindow = document.querySelector('.MuiDataGrid-window')!;
+      gridWindow.scrollTop = 10e6; // scroll to the bottom
+      gridWindow.dispatchEvent(new Event('scroll'));
+
+      let lastCell = document.querySelector('[role="row"]:last-child [role="cell"]:first-child')!;
+      expect(lastCell).to.have.text('995');
+
+      let virtualPage = apiRef!.current!.getState().rendering!.virtualPage;
+      expect(virtualPage).to.equal(98);
+
+      setProps({ nbRows: 9 });
+
+      lastCell = document.querySelector('[role="row"]:last-child [role="cell"]:first-child')!;
+      expect(lastCell).to.have.text('8');
+
+      const renderingZone = document.querySelector('.MuiDataGrid-renderingZone')! as HTMLElement;
+      expect(renderingZone.children.length).to.equal(9);
+
+      virtualPage = apiRef!.current!.getState().rendering!.virtualPage;
+      expect(virtualPage).to.equal(0);
+
+      const isVirtualized = apiRef!.current!.getState().containerSizes!.isVirtualized;
+      expect(isVirtualized).to.equal(false);
+    });
+
     describe('Pagination', () => {
       it('should render only the pageSize', () => {
         render(<TestCaseVirtualization pagination pageSize={32} />);

packages/storybook/src/stories/grid-rows.stories.tsx

@@ -1,5 +1,5 @@
-import Alert from '@material-ui/lab/Alert';
 import * as React from 'react';
+import Alert from '@material-ui/lab/Alert';
 import Typography from '@material-ui/core/Typography';
 import Button from '@material-ui/core/Button';
 import Popper from '@material-ui/core/Popper';
@@ -875,3 +875,42 @@ export function EditCellWithMessageGrid() {
     </div>
   );
 }
+
+export function SwitchVirtualization() {
+  const { data, setRowLength } = useDemoData({
+    dataSet: 'Commodity',
+    rowLength: 200,
+    maxColumns: 20,
+  });
+
+  const handleButtonClick = (nbRows: number) => {
+    setRowLength(nbRows);
+  };
+
+  React.useLayoutEffect(() => {
+    const window = document.querySelector('.MuiDataGrid-window');
+    if (window) {
+      window!.scrollTo(0, 5000);
+    }
+  });
+
+  return (
+    <div
+      style={{
+        display: 'flex',
+        flexDirection: 'column',
+        flex: 1,
+        height: '100%',
+        width: '100%',
+      }}
+    >
+      <div>
+        <Button onClick={() => handleButtonClick(9)}>9 items</Button>
+        <Button onClick={() => handleButtonClick(100)}>100 items</Button>
+      </div>
+      <div style={{ width: '100%', height: 500 }}>
+        <XGrid rows={data.rows} columns={data.columns} />
+      </div>
+    </div>
+  );
+}