add get size helpers

docs/Grid.md

@@ -49,6 +49,14 @@ A windowed grid of elements. `Grid` only renders cells necessary to fill itself
 
 Gets offsets for a given cell and alignment.
 
+##### getTotalRowsHeight
+
+Gets estimated total rows' height.
+
+##### getTotalColumnsWidth
+
+Gets estimated total columns' width.
+
 ##### handleScrollEvent ({ scrollLeft, scrollTop })
 
 This method handles a scroll event originating from an external scroll control.

source/Grid/Grid.jest.js

@@ -613,6 +613,22 @@ describe('Grid', () => {
       expect(scrollTop).toEqual(900);
     });
 
+    it('should support getTotalRowsHeight() public method', () => {
+      const grid = render(getMarkup());
+      grid.recomputeGridSize();
+      const totalHeight = grid.getTotalRowsHeight();
+      // 100 rows * 20 item height = 2,000 total item height
+      expect(totalHeight).toEqual(2000);
+    });
+
+    it('should support getTotalColumnsWidth() public method', () => {
+      const grid = render(getMarkup());
+      grid.recomputeGridSize();
+      const totalWidth = grid.getTotalColumnsWidth();
+      // 50 columns * 50 item width = 2,500 total item width
+      expect(totalWidth).toEqual(2500);
+    });
+
     // See issue #565
     it('should update scroll position to account for changed cell sizes within a function prop wrapper', () => {
       let rowHeight = 20;

source/Grid/Grid.js

@@ -386,6 +386,20 @@ class Grid extends React.PureComponent<Props, State> {
     };
   }
 
+  /**
+   * Gets estimated total rows' height.
+   */
+  getTotalRowsHeight() {
+    return this.state.instanceProps.rowSizeAndPositionManager.getTotalSize();
+  }
+
+  /**
+   * Gets estimated total columns' width.
+   */
+  getTotalColumnsWidth() {
+    return this.state.instanceProps.columnSizeAndPositionManager.getTotalSize();
+  }
+
   /**
    * This method handles a scroll event originating from an external scroll control.
    * It's an advanced method and should probably not be used unless you're implementing a custom scroll-bar solution.