Fix jitter when quickly swiping back and forth between pages (iOS)

[nemophrost]

The problem: After a swipe is complete and the offset is being set in the state, if you keep swiping you can potentially have the ScrollView's internal offset be different than the one you are setting in state. If this is the case, then when the render happens and the offset is passed in as a prop to ScrollView, then it resets the offset to the one specified. The result is that you can be mid-swipe and the pages will jump back partially to the old offset causing some nasty jitter.

The fix: I added this.internals to store calculated values that are used a lot and are passed back to callbacks, but do not directly effect the render (isScrolling and offset). Offset does effect rendering but should only effect it when the size changes or if total pages changes. So offset is stored in this.internals most of the time and it's occasionally saved to the state to force the ScrollView to update. You will notice the callbacks that were getting this.state passed to them now get this.fullState() which includes state and internals.

[leecade]

very nice. Some issues mentioned the problem before.

[leecade]

Hi @nemophrost

I found a problem in this PR. Breaking the consistent scroll animate direction in loop mode.

Reproduce:

loop=true

if press the right button, run a loop: 1->2->3->1

but now we see the wrong animation when 3->1.

Please check again and help me fix it.

[nemophrost]

@leecade oh yeah, that makes sense. I'll fix that with a new PR

[leecade]

@nemophrost great 👍

[nemophrost]

@leecade #260 fixes it. Not the most elegant solution, but after several house of trying lots of other things, it at least works consistently. I'm open to better ideas for sure :)

[fungilation]

Nice. I think this fixes issue I've been using a workaround for in #172?

[Quenton2018]

每次循环结束后会闪屏一下