8277785: ListView scrollTo jumps to wrong location when CellHeight is changed #808

johanvos · 2022-07-04T13:52:40Z

In order to fix the issues reported in JDK-8089589, the VirtualFlow now uses the real sizes of the elements that are displayed. This allows for a more natural way of scrolling through lists that contain items of very different sizes.
The algorithm that is used, does not calculate the size of each individual cell upfront, as that would be a major performance overhead (especially for large lists). Instead, we estimate the total size and the size of the individual cells based on the real measured size of a (growing) number of cells.

There are a number of key variables that depend on this estimated size:

position
aboluteOffset
currentIndex

As a consequence, when the estimated size is changing, the absoluteOffset may change which may lead to a new currentIndex. If this happens during a layout phase, or a "complex" operation (e.g. scroll to an item and select it), this may lead to visually unexpected artifacts. While the rendering becomes more "correct" when the estimated size is improving, it is more important that we do not create visual confusion.

The difficulty is that there are a large number of ways to manipulate the VirtualFlow, and different entry points may have different expectations about which variables should be kept constant (or only changed gradually).

In this PR, we focus on consistency in the scrollTo method, where we want to keep the top-cell constant. In case the estimated size is improved during the scrollTo execution, or the next layoutChildren invocation, this implies keeping the result of computeCurrentIndex() constant so that after scrolling to a cell and selecting it, the selected cell is indeed the one that is scrolled to.

This PR contains a number of tests for this scrollTo behaviour, that should also be considered as regression test in case we want to add more invariants later.

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Issue

JDK-8277785: ListView scrollTo jumps to wrong location when CellHeight is changed

Reviewers

Kevin Rushforth (@kevinrushforth - Reviewer)
Florian Kirmaier (@FlorianKirmaier - Author)
Ajit Ghaisas (@aghaisas - Reviewer)

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Checkout this PR locally:
$ git fetch https://git.openjdk.org/jfx pull/808/head:pull/808
$ git checkout pull/808

Update a local copy of the PR:
$ git checkout pull/808
$ git pull https://git.openjdk.org/jfx pull/808/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 808

View PR using the GUI difftool:
$ git pr show -t 808

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Download this PR as a diff file:
https://git.openjdk.org/jfx/pull/808.diff

… and currentIndex are all subject to change when the total estimated size of the entire list is changing. Improvements in the estimated size should not lead to sudden changes during the layout phase.

bridgekeeper · 2022-07-04T13:53:15Z

👋 Welcome back jvos! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

mlbridge · 2022-07-04T14:00:23Z

Webrevs

mstr2 · 2022-07-04T16:32:21Z

The proposed PR also fixes the issue with setPosition described here.

kevinrushforth · 2022-07-05T21:43:05Z

/reviewers 2

openjdk · 2022-07-05T21:43:52Z

@kevinrushforth
The total number of required reviews for this PR (including the jcheck configuration and the last /reviewers command) is now set to 2 (with at least 1 Reviewer, 1 Author).

kevinrushforth

The fix looks good to me, although I did leave a question about one of the boundary checks. This will need additional testing. Several of the assertEquals calls have the expected and actual args backwards. I also left a few minor formatting comments (I didn't note all of them).

modules/javafx.controls/src/main/java/javafx/scene/control/skin/VirtualFlow.java

modules/javafx.controls/src/test/java/test/javafx/scene/control/ListViewTest.java

modules/javafx.controls/src/test/java/test/javafx/scene/control/ListViewKeyInputTest.java

johanvos · 2022-07-07T10:12:58Z

The fix looks good to me, although I did leave a question about one of the boundary checks. This will need additional testing. Several of the assertEquals calls have the expected and actual args backwards. I also left a few minor formatting comments (I didn't note all of them).

I did a reformat on the sections that you mentioned. Doing a reformat with NetBeans on the whole file would cause too many changes that would hide the real changes, so that is probably a bit too much?

kevinrushforth · 2022-07-07T22:04:47Z

I did a reformat on the sections that you mentioned. Doing a reformat with NetBeans on the whole file would cause too many changes that would hide the real changes, so that is probably a bit too much?

Perfect (and yes, I prefer to only reformat the sections being modified).

kevinrushforth

I noted a couple more assertEquals calls where it looks like the expected and actual are backwards. The rest looks good. I'll finish my testing tomorrow.

modules/javafx.controls/src/test/java/test/javafx/scene/control/ListViewKeyInputTest.java

modules/javafx.controls/src/test/java/test/javafx/scene/control/ListViewTest.java

Reverse expected and actual args in some tests.

FlorianKirmaier · 2022-07-11T11:42:52Z

I've retested this version of the PR, and I can confirm, that it fixes the bug in the real-world application! So no regression happened when moving to the new PR! So great work!

Not sure whether the first two tests are still necessary.
The tests I wrote, basically used these test as a template and tried to generalize/parametrize it. But I guess more tests don't do any harm.

There are 2 issues, we shouldn't forget about after this PR:

1.) In my original tests I had a snippet which is removed in this version. I still think the test is correct but it fails. So we should investigate it.

// After clicking, the cells shouldn't move
listView.getSelectionModel().select(scrollToIndex);
listView.requestLayout();
Toolkit.getToolkit().firePulse();
assertEquals("Upper cell shouldn't move after changing heights and clicking", previousLayoutY, scrollToCell.getLayoutY(), 1.);

2.)
In the previous PR we reported issues when scrolling after jumping to an index - including a video. As discussed with Johan we would like to investigate this further after this PR.

kevinrushforth · 2022-07-11T12:52:43Z

I think you missed one place where the assertEquals args are backwards. See #808 (comment)

I'll do final testing today, but so far everything looks good.

kevinrushforth

Looks good.

openjdk · 2022-07-12T13:20:45Z

@johanvos This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8277785: ListView scrollTo jumps to wrong location when CellHeight is changed

Reviewed-by: kcr, fkirmaier, aghaisas

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 18 new commits pushed to the master branch:

eb8e9ef: 8289606: CustomSecurityManagerTest fails on Mac M1
b9a1ec5: 8288137: The set of available printers is not updated without application restart
0132ac8: 8284676: TreeTableView loses sort ordering when applied on empty table
8d5d3ca: 8268225: Support :focus-visible and :focus-within CSS pseudoclasses
437c078: 8289255: update Eclipse .classpath and other configuration files
13f3e1f: 8289395: Fix warnings: Varargs methods should only override or be overridden by other varargs methods
c7d3fd9: 8283402: Update to gcc 11.2 on Linux
cbb53b2: 8289952: Visual Studio libs msvcp140_1.dll and msvcp140_2.dll missing from build
187fbe1: 8289381: Fix warnings: The assignment to variable has no effect
60c75b8: 8274771: Map, FlatMap and OrElse fluent bindings for ObservableValue
... and 8 more: https://git.openjdk.org/jfx/compare/b3eca1f64977343c06e6035fab385935055b6d6b...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

Maran23 · 2022-07-12T13:45:13Z

modules/javafx.controls/src/main/java/javafx/scene/control/skin/VirtualFlow.java

        if (needsRecreateCells) {
            lastWidth = -1;
            lastHeight = -1;
            releaseCell(accumCell);
-//            accumCell = null;


Is this intentional or did you may forgot to add back this two lines of code?

This is intentional -- it was already moved to comments, and there is no need to destroy the accumCell (releasing it is what we need)

johanvos · 2022-07-14T09:40:39Z

/integrate

openjdk · 2022-07-14T09:42:04Z

Going to push as commit b8302f6.
Since your change was applied there have been 18 commits pushed to the master branch:

eb8e9ef: 8289606: CustomSecurityManagerTest fails on Mac M1
b9a1ec5: 8288137: The set of available printers is not updated without application restart
0132ac8: 8284676: TreeTableView loses sort ordering when applied on empty table
8d5d3ca: 8268225: Support :focus-visible and :focus-within CSS pseudoclasses
437c078: 8289255: update Eclipse .classpath and other configuration files
13f3e1f: 8289395: Fix warnings: Varargs methods should only override or be overridden by other varargs methods
c7d3fd9: 8283402: Update to gcc 11.2 on Linux
cbb53b2: 8289952: Visual Studio libs msvcp140_1.dll and msvcp140_2.dll missing from build
187fbe1: 8289381: Fix warnings: The assignment to variable has no effect
60c75b8: 8274771: Map, FlatMap and OrElse fluent bindings for ObservableValue
... and 8 more: https://git.openjdk.org/jfx/compare/b3eca1f64977343c06e6035fab385935055b6d6b...master

Your commit was automatically rebased without conflicts.

openjdk · 2022-07-14T09:42:21Z

@johanvos Pushed as commit b8302f6.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

nicholas-os · 2022-07-15T01:17:16Z

This fix seems to break TreeTableView. The tree jumps to the top when a TreeItem is expanded or collapsed. Tested with 19-ea-9. Does not happen when running the same application with 19-ea-8.

kevinrushforth · 2022-07-15T15:14:17Z

This fix seems to break TreeTableView.

A new bug has been filed to track this: JDK-8290348.

Add more consistency between key-values. The position, absoluteOffset…

55f6ba9

… and currentIndex are all subject to change when the total estimated size of the entire list is changing. Improvements in the estimated size should not lead to sudden changes during the layout phase.

openjdk bot added the rfr Ready for review label Jul 4, 2022

kevinrushforth requested review from kevinrushforth, aghaisas and FlorianKirmaier July 5, 2022 21:46

kevinrushforth reviewed Jul 6, 2022

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kevinrushforth mentioned this pull request Jul 6, 2022

[WIP] 8277785: ListView scrollTo jumps to wrong location when CellHeight is changed #712

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Add link to issue about ignored test

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Reverse expected and actual args in some tests.

reverse one more expected/actual set of args.

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kevinrushforth approved these changes Jul 12, 2022

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FlorianKirmaier approved these changes Jul 12, 2022

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openjdk bot added the ready Ready to be integrated label Jul 12, 2022

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8277785: ListView scrollTo jumps to wrong location when CellHeight is changed #808

8277785: ListView scrollTo jumps to wrong location when CellHeight is changed #808

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8277785: ListView scrollTo jumps to wrong location when CellHeight is changed #808

8277785: ListView scrollTo jumps to wrong location when CellHeight is changed #808

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