On Wed, 30 Mar 2022 13:27:40 GMT, Johan Vos <[email protected]> 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 don't believe that it is possible to position the content and scrollbar
**exactly**, if the VirtualFlow **estimates** the size of the cells.
For that case we need an external cell size provider, that I, as an application
developer, can provide to the e.g. ListView.
I thought of something like this. The existing estimation logic can then be
implemented as a default cell size provider.
interface CellSizeProvider {
/**
* Returns the size of all cells.
* IMPORTANT: Be carefully by implementing this method. It can drastically
degrade the performance of a component.
*/
double getTotalSize();
/**
* Returns the size of the cell for an item given by its index.
* IMPORTANT: Be carefully by implementing this method. It can drastically
degrade the performance of a component.
*/
double getCellSize(int);
/**
* The callback which is set by the VirtualFlow. It allows to calculate the
cell size for an item given by its index.
* IMPORTANT: This callback returns the exact value, but it may be slow.
*/
void setCellSizeCalculator(Function<Integer, Double> cellSizeCalculator);
}
-------------
PR: https://git.openjdk.java.net/jfx/pull/712
