Optimizations and other refactor

[pdpino]

Problem

The component may run into performance issues when rendering too many days/weeks, and/or too many events. For example this happens with 500 evts:

demo-500-evts-2022-05-24_23.47.01.mp4

• See the VirtualizedList warning
• There are dropped frames when scrolling
• Drag and dropping one event takes a lot of time (specifically, dropping the event is very slow)

Possible causes

• When only one event is modified --> the events prop changes --> all Events are re-rendered (e.g. when dragging an event)
• Each item of the VirtualizedList is too heavy/complex
• When scrolling horizontally, the page appending and prepending is done in place (I don't even remember why 😅)
• When moving to a distant date (e.g. with goToDate()), many pages have to be added to the lists (see for example: onSwipeNext stuck  #207)

(I've been using android systrace for profiling, but is still a limited tool)

What now

I've been trying to improve these, not only for performance, but also for other features, for example:

1. The horizontal pinch-gesture (Add PinchGestureHandler #130) will probably require a refactor to the VirtualizedList items. Implementation details: (skip if wanted)
   • Currently each item passed to the VirtualizedList represents one page of numberOfDays (e.g. 7 days)
   • This implies that when numberOfDays changes, the items must be recalculated and re-rendered from scratch to align items with pages (even though the events are the same). (See componentDidUpdate() here)
   • A possible solution is to design each item to represent one day --> a change in numberOfDays would not require recalculating the items
2. Such refactor would allow fixing much more easily Select number of days scrolled #128, wrong date with fixedHorizontally #141 (comment), Selected Date Position. #185, goToNextDay & goToPreviousDay #186
3. I want to create a first version of a <MonthView> component (Month View. #95) with these considerations in mind

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@hoangnm any thoughts? I'll probably be submitting some PRs

cc: @rdewolff, @Salmankhan033, @Vidxyz

[greenboots88]

@pdpino @hoangnm the performance issues being experienced here and in #259 is due to the VirtualizedList. If you use your old library version from 2 years ago without VirtualizedList, the performance and speed is much better.

[pdpino]

@greenboots88 thanks, good to know!

Can you confirm which version/commit did you use? The VirtualizedList was introduced after 0.0.19