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Allow ScrollView to be controllable via scrollTop #740

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Allow ScrollView to be controllable via scrollTop #740

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d0abdd4
Allow scroll top to be data bound
joefiorini Jan 30, 2020
750f777
Make ScrollView fully controllable
joefiorini Jan 30, 2020
ea43ba3
Fix CI
joefiorini Jan 30, 2020
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21 changes: 20 additions & 1 deletion examples/ScrollView.re
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Original file line number Diff line number Diff line change
Expand Up @@ -26,9 +26,27 @@ let innerBox =

module Sample = {
let%component make = () => {
let%hook (scrollTop, setScrollTop) = Hooks.state(0);
let%hook (bounce, setBounce) = Hooks.state(true);

let handleScrollTop = s => setScrollTop(_ => Float.to_int(s));
Console.out("scrollTop: ");
Console.log(scrollTop);

<View style=containerStyle>
<Text
text="Scroll top"
style=Style.[
marginBottom(10),
fontFamily("Roboto-Regular.ttf"),
fontSize(20.),
]
/>
<Slider
onValueChanged=handleScrollTop
value={Float.of_int(scrollTop)}
maximumValue=450.0
/>
<Text
text="Bounce"
style=Style.[
Expand All @@ -42,7 +60,8 @@ module Sample = {
checked=bounce
style=Style.[marginBottom(10)]
/>
<ScrollView style=outerBox bounce>
<ScrollView
style=outerBox bounce scrollTop onScroll={v => setScrollTop(_ => v)}>
<Image
src="outrun-logo.png"
/* Exercise the case in #579 */
Expand Down
31 changes: 27 additions & 4 deletions src/UI_Components/ScrollView.re
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Original file line number Diff line number Diff line change
Expand Up @@ -47,6 +47,7 @@ let%component make =
~scrollLeft=0,
~scrollTop=0,
~bounce=defaultBounce,
~onScroll=?,
~children=React.empty,
(),
) => {
Expand All @@ -56,6 +57,19 @@ let%component make =
Hooks.state(None);
let%hook (actualScrollLeft, setScrollLeft) = Hooks.state(scrollLeft);
let%hook (bouncingState, setBouncingState) = Hooks.state(Idle);
let%hook () =
Hooks.effect(
Always,
() => {
if (scrollTop != actualScrollTop) {
switch (onScroll) {
| Some(_) => dispatch(ScrollUpdated(scrollTop))
| None => ()
};
};
None;
},
);
Comment on lines +60 to +72
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@glennsl glennsl Jan 30, 2020 •
edited
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I don't think this will work if ~scrollTop is omitted, since it would then always reset to 0, its default value. So either scrollTop and onScroll needs to be mandatory, which I don't think is desirable, or scrollTop needs to be optional but without a default value so this can be skipped if it's not set.

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@glennsl I just tested it by adding an additional ScrollView to the example and leaving off the onScroll and scrollTop. Everything seemed to work fine in that case. Then I passed just a scrollTop and it rendered as expected. Are you referring to a case where scrollTop is missing but onScroll is provided?

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Hmm, yeah that's a necessary condition too. It should check for the presence of scrollTop instead of onScroll. It's not very intuitive that hard-coding scrollTop and not setting onScroll would result in scrollTop being ignored.

I also don't think the effect hook is really necessary, and mostly just complicates the logic. Instead you could rename actualScrollTop to something like InternalScrollTop and then set actualScrollTop to scrollTop if present, or internalScrollTop if not.


let%hook (actualScrollTop, _bounceAnimationState, resetBouncingAnimation) =
switch (bouncingState) {
Expand Down Expand Up @@ -114,11 +128,18 @@ let%component make =

let isVerticalScrollbarVisible = maxHeight > 0;
let isHorizontalScrollbarVisible = maxWidth > 0;
let updateScrollPos = v => {
dispatch(ScrollUpdated(v));
switch (onScroll) {
| Some(f) => f(v)
| None => ()
};
};

let verticalScrollBar =
isVerticalScrollbarVisible
? <Slider
onValueChanged={v => dispatch(ScrollUpdated(int_of_float(v)))}
onValueChanged={v => updateScrollPos(int_of_float(v))}
minimumValue=0.
maximumValue={float_of_int(maxHeight)}
sliderLength={outerMeasurements.height}
Expand Down Expand Up @@ -170,11 +191,13 @@ let%component make =
| Bouncing(_) => ()
| Idle when !bounce && (isAtTop || isAtBottom) =>
let clampedScrollTop = isAtTop ? 0 : maxHeight;
dispatch(ScrollUpdated(clampedScrollTop));
updateScrollPos(clampedScrollTop);
| Idle when bounce && (isAtTop || isAtBottom) =>
setBouncingState(_ => Bouncing(- delta * 2));
dispatch(ScrollUpdated(isAtTop ? 0 : maxHeight));
| Idle => dispatch(ScrollUpdated(newScrollTop))
updateScrollPos(isAtTop ? 0 : maxHeight);
| Idle =>
dispatch(ScrollUpdated(newScrollTop));
updateScrollPos(newScrollTop);
};
};
(horizontalScrollbar, verticalScrollBar, scroll);
Expand Down