ScrollableView should notify me when it is and the end of the scrolling

[cjolif]

In order to be able to for example get additional data when reaching the end of a list I need to be notified when the ScrollableView is reaching the end of a list.

[cjolif]

current solution is to override adjustDestination and use the method parameters to compute if we are out of the range, however an event might simplify this. As we have already a solution put it low priority.

[cjolif]

actually adjustDestination does not fit exactly my needs because it waits for the touch interaction to end before being notified where in my case I want to start refreshing seamlessly without ending initial interaction.

[Sebastien Brunot]

I suggest to add scroll events to scrollable (beforescroll and afterscroll) to be notified of scrolling. Each scroll event will contain the following attributes:

• x: x coordinate of the scroll destination;
• y: y coordinate of the scroll destination;
• beforeTop: a boolean that is true if the scroll detination is before the top of the scrollable;
• beforeTopHeight: the number of pixels before the top of the scrollable for the scroll destination;
• afterBottom: a boolean that is true if the scroll destination is after the bottom of the scrollable;
• afterBottomHeight: the number of pixels after the bottom of the scrollable for the scroll destination.

I will be possible to cancel a scroll in the beforescroll event handler, by returning the value false.

I also propose to update the resize method of ScrollableView so that if the view is resized while scrolling is perfomed, the dimensions are updated accordingly and the scroll bars are also resized accordingly (which is not currently the case).

I'm attaching a patch with an implementation proposal.

[Sebastien Brunot]

Add scroll events to scrollable (beforescroll and afterscroll), and fix the ScrollableView resize method so that it works properly when called during a scroll (IBM CCLA).

[cjolif]

In [30919]:

fixes #16587. Add scroll events to scrollable (beforescroll and afterscroll), and fix the ScrollableView? resize method so that it works properly when called during a scroll. Thanks Sebastien Brunot (IBM CCLA). !strict.

[Sebastien Brunot]

pull to refresh example using scrolling events (IBM CCLA).

[Sebastien Brunot]

I'm adding an example of a "pull to refresh" implementation using the new scroll events.

[Sebastien Brunot]

image referenced in pullToRefresh.patch (IBM CCLA).

[Sebastien Brunot]

image referenced in pullToRefresh.patch (IBM CCLA).

[cjolif]

In [30960]:

refs #16587. prevent sending events when not needed and pull to refresh example using scrolling events. Thanks Sebastien Brunot (IBM CCLA). !strict.