fix(react-grid): change processing of last page in lazy load mode (#2067

)
DevExpress · Jun 6, 2019 · 2b52fe0 · 2b52fe0
1 parent 35c4642
commit 2b52fe0
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Showing 2 changed files with 20 additions and 9 deletions.
diff --git a/packages/dx-grid-core/src/plugins/virtual-table-state/helpers.test.ts b/packages/dx-grid-core/src/plugins/virtual-table-state/helpers.test.ts
@@ -203,6 +203,14 @@ describe('VirtualTableState helpers', () => {
         expect(calculateRequestedRange(loadedInterval, newInterval, 399, pageSize))
           .toEqual({ start: 300, end: 500 });
       });
+
+      it('should correctly process the last page', () => {
+        const loadedInterval = createInterval(0, 200);
+        const newInterval = createInterval(1000, 1200);
+
+        expect(calculateRequestedRange(loadedInterval, newInterval, 1180, pageSize))
+          .toEqual({ start: 1000, end: 1200 });
+      });
     });
 
     describe('fast scroll', () => {

diff --git a/packages/dx-grid-core/src/plugins/virtual-table-state/helpers.ts b/packages/dx-grid-core/src/plugins/virtual-table-state/helpers.ts
@@ -45,16 +45,19 @@ export const mergeRows: MergeRowsFn = (
 export const calculateRequestedRange: CalculateRequestedRangeFn = (
   loadedInterval, newRange, referenceIndex, pageSize,
 ) => {
-  if (Math.abs(loadedInterval.start - newRange.start) >= 2 * pageSize) {
-    const useFirstHalf = referenceIndex % pageSize < pageSize / 2;
-    const start = useFirstHalf
-      ? newRange.start
-      : newRange.start + pageSize;
-    const end = Math.min(newRange.end, start + 2 * pageSize);
-
-    return { start, end };
+  const isAdjacentPage = Math.abs(loadedInterval.start - newRange.start) < 2 * pageSize;
+  if (isAdjacentPage) {
+    return intervalUtil.difference(newRange, loadedInterval);
   }
-  return intervalUtil.difference(newRange, loadedInterval);
+
+  const useFirstHalf = referenceIndex % pageSize < pageSize / 2;
+  const isLastPage = intervalUtil.getLength(newRange) / pageSize < 3;
+  const start = useFirstHalf || isLastPage
+    ? newRange.start
+    : newRange.start + pageSize;
+  const end = Math.min(newRange.end, start + 2 * pageSize);
+
+  return { start, end };
 };
 
 export const rowToPageIndex: PureComputed<[number, number]> = (