More than 9 items in the data causes the Carousel to re-render all the items indefinitely

[amitassaraf]

Is this a bug report or a feature request?

Bug report

Have you read the guidelines regarding bug report?

Yes.

Have you read the documentation in its entirety?

Yes.

Have you made sure that your issue hasn't already been reported/solved?

Yes.

Is the bug specific to iOS or Android? Or can it be reproduced on both platforms?

I only have an iOS device so I am not sure.

Is the bug reproductible in a production environment (not a debug one)?

Yes.

Have you made sure that it wasn't a React Native bug?

Yes

Have you been able to reproduce the bug in the provided example?

Yes

Environment

Environment:
React: 16.2.0
React native: 0.49.0
react-native-snap-carousel: 3.7.0

Target Platform:
iOS (8.0)

Steps to Reproduce

1. Render a carousel with 9 items and console.log when the renderItem function is called.
2. See that it only renders the items once, as it should.
3. Then add a 10th item to the data array, and see how the renderItem methods is called indefinitely on every item.

<Carousel
                            data={[{a: '2'}, {a: '44'}, {a: '21'}, {a: '2'}, {a: '33'}, {a: '11'}, {a: '6'}, {a: '77'}, {a: '99'}, {a: '01'}]}
                            renderItem={({item, index}) => {
                                console.log('== RENDER ITEM == ' + index);
                                return <View />
                            }}
                            sliderWidth={Window.width}
                            itemWidth={Window.width}
                        />

Expected Behavior

I thought that I would only see render calls to the items that are visible and the rest would only be called ONCE they are visible.

Actual Behavior

The carousel constantly rerenders the items non stop.

[bd-arc]

Hi @amitassaraf,

This clearly looks like a React Native bug. First, have you made sure that your carousel is not a child of a ScrollView component? (see here for more info)

Then, does the issue persist with a newer version of React Native? The FlatList component upon which the plugin is based is known to be pretty buggy. The Facebook team sometimes fixes some of them; this is worth a try ;-)

[amitassaraf]

@bd-arc Yes the Carousel is definitely not a direct child of ScrollView. React Navigation might be using a ScrollView somewhere, could this be the issue?

[bd-arc]

@amitassaraf I can't find the exact issue again, but I remember reading that when a FlatList is a child of a ScrollView (this includes FlatList, VirtualizedList and many plugins) it apparently renders all child components, even those currently off-screen.

This may have been fixed since then; that's why I recommend that you try with a newer version of React Native.

[amitassaraf]

@bd-arc I upgraded to 0.55 with no luck. I will tomorrow try to use the carousel on a page outside the React Navigation cycle to see if it works. Maybe React Navigation uses a ScrollView of some sorts.

Even if this solves it I have no idea what to do, because I need React Navigation haha :) Maybe I'll look for a different navigation library :/

[amitassaraf]

@bd-arc I have tested this in a sandbox environment and it still happens. Just use a carousel and add 10+ objects and it will infinitely render the items.

                <Carousel
                    data={[{id: 1}, {id: 2}, {id: 3}, {id: 4}, {id: 5}, {id: 6}, {id: 7}, {id: 8}, {id: 9}, {id: 10}, {id: 11}]}
                    enableSnap={true}
                    enableMomentum={true}
                    renderItem={({item, index}) => {
                        console.log('== RENDER ITEM ' + index);
                        return <Text>{item.id}</Text>
                    }}
                    keyExtractor={item => String(item.id)}
                    firstItem={1}
                    sliderWidth={Window.width}
                    itemWidth={Window.width * 0.85}
                />

[bd-arc]

@amitassaraf Can you try the same thing with a regular FlatList component and see if it behaves the same? We need to determine if this is a FlatList ou a Carousel bug.

Note that you can keep your data and renderItem props exactly the same.

[oidoug]

I'm using the carousel as a pager, loading large local images and I'm having the same problem, but in addition, some random itens do not show. It gets worse from page 10-12 ahead.

Using a PureComponent helped with unnecessary renders, but pages are still blank randomly.

I'm now trying to isolate the problem and will update if I find something useful. Thanks.

[bd-arc]

@douglaslondrina I'm definitely interested in your findings. If this is an issue with the plugin itself, I'll have to work on a fix; if this has to do with the FlatList, let's hope we can hack our way out.

[amitassaraf]

@bd-arc I'll check tomorrow. My hack around this was to check inside the renderItem method if the index is the currentIndex +- 1 and only then render my element, otherwise return null :/

[oidoug]

The problem really seams to be with FlatList, I tried it isolated and still got weird blank pages on android real devices (on emulator it works ok). I'm on a tight schedule and am working now with https://github.com/Flipkart/recyclerlistview lib, but I'll investigate it further as soon as possible.

[UdaraJay]

Any update on this? Ran into the same issue...

[sridhard]

Any update on this? Ran into the same issue...

[sridhard]

This is same as #349 ..Please check