RFR: 8277785: ListView scrollTo jumps to wrong location when CellHeight is changed [v4]

[François Martin]

On Wed, 30 Mar 2022 13:27:40 GMT, Johan Vos <jvos at openjdk.org> wrote:

>> When the size of a ListCell is changed and a scrollTo method is invoked without having a layout calculation in between, the old (wrong) size is used to calculcate the total estimate. This happens e.g. when the size is changed in the `updateItem` method.
>> This PR will immediately resize the cell and sets the new value in the cache containing the cellsizes.
>
> Johan Vos has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Don't shift cells if we are already showing the lowest index cell.

I noticed this bug as well, but in my case even when the `CellHeight` stays the same (so I'm not sure if it's the same or something else)... A minimal repro example:

public class ApplicationUI extends VBox {
    private final ObservableList<String> elements = FXCollections.observableArrayList();
    public ApplicationUI() {
        Button button = new Button("Add New Element");
        ListView<String> listView = new ListView<>(elements);
        setVgrow(listView, Priority.ALWAYS);
        getChildren().addAll(listView, button);
        button.setOnAction(event -> {
            elements.add(String.valueOf(elements.size()));
        });
        elements.addListener((ListChangeListener<String>) c -> {
            while (c.next()) {
                listView.scrollTo(c.getFrom());
            }
        });
    }
}


Click the button until there is a scroll bar, it always seems to scroll down to the second last element in the list, instead of the last.

Interestingly, changing the line from `listView.scrollTo(c.getFrom());` to `listView.scrollTo(c.getFrom()-1);` or `listView.scrollTo(c.getFrom()+1);` results in the same behavior, however changing it to `listView.scrollTo(c.getFrom()-2);` does scroll correctly to the last item in the list?

Just thought I would share this in case this would help find the issue.

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PR: https://git.openjdk.java.net/jfx/pull/712