Inserting at the top, while at the top, always scrolls the view about famous-flex

[mcbain]

Did you code these behavior somewhere?
Because just rendering the new item positions would move all existing item down by the size of the inserted element.

[IjzerenHein]

When you insert at the top, it typically shouldn't scroll unless there are less items than would fit on the screen (this will cause the scrollview to ensure that no items are accidentally hidden from view).

Actually, now you mention it, I'm seeing sort of a bug with inserting at the top. It always seems to scroll down which isn't correct. When you manually scroll down a couple items, and then press + to insert, it works as expected and it doesn't influence the scroll position.
I'll have a look at this as it used to work, but must have gotten broken along the way,

[mcbain]

For my project i tried to implement some kind of function which needs to compensate flickering by changing the scroll position. In the end the code was too complicated to get it production ready, when elements can be inserted at any position and other elements can also change size.
So i'm very keen on understanding your solution :)

[IjzerenHein]

Ah I see :)

Well, the FlexScrollView is a completely new ScrollView implementation, it bares little resemblance to the stock famo.us ScrollView. I wrote it out of a necessity to support more flexible layouts such as multiple columns and sticky column-headers. The FlexScrollView is based on ScrollController which in turn is based on LayoutController. I also wrote it support better handling for true-size renderables and making bottom alignment possible for scrollviews.

I'm not even sure where to begin explaining how it all works :)
Basically, the FlexScrollView takes care of the scrolling behavior and rendering and the ListLayout takes care of the layouting. The ListLayout tells the scrollview where to place an item, and when the scrollview sees that an item is at a new position, it uses particles & springs to move the renderable to the new position.

[mcbain]

"when the scrollview sees that an item is at a new position" where can i find such code?

[IjzerenHein]

So when flow-mode is enabled, the ListLayout writes the new translate coordinates to a FlowLayoutNode. FlowLayoutNode is derived from LayoutNode and contains properties such as: size, translate, origin, align, opacity, skew, scale & rotate. it basically holds the new intended state for a layout item. FlowLayoutNode contains a particle and a spring for each of these properties. It sets the end-state of the spring (e.g. for the translate coordinates) which causes the particle to move towards that new end-state. The scrollView then asks the FlowLayoutNode (which are managed by LayoutNodeManager) for the current render-spec every render-cycle (getSpec).

[IjzerenHein]

I fixed the bug I mentioned earlier. When the view was at the top, and you inserted an item at index 0 (before the first item), it would always scroll to the newly inserted item, which is incorrect. It should not scroll at all when inserting. This problem has been fixed.