RFR: JDK-8311983: ListView sometimes throws an IndexOutOfBoundsException

[Marius Hanl]

On Thu, 3 Aug 2023 11:41:30 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

>> An IOOBE was thrown when scrolling up via the trough (-> `VirtualScrollBar#adjustValue`).
>> This happened only when it has bigger cells than the viewport. 
>> If the the uppermost cell with the index 0 is only visible (although not completely scrolled to the top) and then an attempt is made to scroll up again, the `VirtualFlow` will try to scroll to the next cell, subtracting index 0 by 1, resulting in -1 -> IOOBE.
>> 
>> The code now guards against any under or overflow.
>> 
>> This is technically a regression from https://bugs.openjdk.org/browse/JDK-8173321
>> 
>> Note: While testing with very big cells, I found out that scrolling via the trough may not work after the first time. 
>> This is because the `VirtualFlow` still creates 2 cells, although only one can be visible at a time (and `VirtualScrollBar` does this check, which will never be true then: `firstVisibleCell == lastVisibleCell`). This is unrelated to this fix. I can create a ticket when I have more information.
>
> modules/javafx.controls/src/main/java/com/sun/javafx/scene/control/VirtualScrollBar.java line 144:
> 
>> 142:                     index = Math.max(0, index - 1);
>> 143:                 } else {
>> 144:                     index = Math.max(flow.getCellCount(), index + 1);
> 
> Shouldn't this be Math.min?

Yes indeed, leftover from testing.

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PR Review Comment: https://git.openjdk.org/jfx/pull/1194#discussion_r1283094443