RFR: 8177945: Single cell selection flickers when adding data to TableView

[Kevin Rushforth]

On Wed, 4 Nov 2020 17:25:16 GMT, Jose Pereda <jpereda at openjdk.org> wrote:

> As discussed in the JBS [issue](https://bugs.openjdk.java.net/browse/JDK-8177945), there are some inconsistencies in the use of `VirtualContainerBase::requestRebuildCells` from `VirtualContainerBase::updateItemCount()`, which is implemented in the different skin classes for virtualised controls `TableViewSkinBase`, `ListViewSkin` or `TreeTableViewSkin`.
> 
> The latter already commented out this call (related to JDK-8155798 and JDK-8147483). 
> 
> This PR removes now the calls to `VirtualContainerBase::requestRebuildCells` from `TableViewSkinBase`  (except for the case `itemCount = 0` based on JDK-8118897 and JDK-8098235) and `ListViewSkin`.
> 
> A test is provided for TableView, that verifies that the `selected` pseudo-class state remains set for the selected cell while adding more items. Without this fix, as the cells are rebuilt, the pseudo-class states are clean and set all over again, thus the flickering.
> 
> For ListView, the test rt_35395 (JDK-8091726) is updated, as now there are way less calls to updateItem.

The fix looks good with one question and one minor suggestion.

modules/javafx.controls/src/main/java/javafx/scene/control/skin/ListViewSkin.java line 359:

> 357: 
> 358:         updatePlaceholderRegionVisibility();
> 359:         if (newCount == oldCount) {

Does this also need the same `else if (oldCount == 0)` test that you added to `TableViewSkinBase`?

modules/javafx.controls/src/test/java/test/javafx/scene/control/TableViewTest.java line 5482:

> 5480: 
> 5481:     @Test
> 5482:     // see JDK-8177945

Minor: It seems best to not have the comment between the annotation and the method being annotated. I see this pattern also in `VirtualFlowTest`, but you might want to move the comment above the annotation.

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PR: https://git.openjdk.java.net/jfx/pull/348