Im looking for insight on how best to implement a loadMore function in the onEndReached callback provided by flatlist while using apollo hooks! I've got it sort of working except every time i load more results the list jumps to the top since the data field of flatlist relies on incoming data from useQuery that changes every time it asks for more...
I dont know if i should be implementing offset and limit based pagination, cursor based, or some other strategy.
If anyone has tips that would be huge! thanks!
I am using Shopify storefront graphql queries to get product list, and here is how I have implemented pagination using cursor-based pagination method on FlatList. Hope you find something usable.
First, declare two variables which will be used later to check whether the Flatlist scrolled and reached on the end.
// declare these two variables
let isFlatlistScrolled = false;
let onEndReachedCalledDuringMomentum = false;
Now, create a method called handleFlatlistScroll which will be used to changed the values of the variable isFlatlistScrolled when the flatlist is scrolled.
const handleFlatlistScroll = () => {
isFlatlistScrolled = true;
};
Also declare a method to change the value of onEndReachedCalledDuringMomentum.
const onMomentumScrollBegin = () => {
onEndReachedCalledDuringMomentum = false;
}
Now, create your flatlist like this :
return (
<Layout style={{ flex: 1 }}>
<Query
query={GET_PRODUCT_LIST_BY_COLLECTION_HANDLE}
variables={{
handle: props.route.params.handle,
cursor: null,
}}>
{({
loading,
error,
data,
fetchMore,
networkStatus,
refetch,
stopPolling,
}) => {
if (loading) {
return <ProductListPlaceholder />;
}
if (data && data.collectionByHandle?.products?.edges?.length > 0) {
stopPolling();
return (
<FlatList
data={data.collectionByHandle.products.edges}
keyExtractor={(item, index) => item.node.id}
renderItem={renderProductsItem}
initialNumToRender={20}
onScroll={handleFlatlistScroll}
onEndReached={() => {
if (
!onEndReachedCalledDuringMomentum &&
isFlatlistScrolled &&
!isLoadingMoreProducts &&
!loading &&
data.collectionByHandle?.products?.pageInfo?.hasNextPage
) {
onEndReachedCalledDuringMomentum = true;
setLoadingMoreProductsStatus(true);
// your loadmore function to fetch more products
}
}}
onEndReachedThreshold={Platform.OS === 'ios' ? 0 : 0.1}
onMomentumScrollBegin={onMomentumScrollBegin}
// ... your other flatlist props
/>
);
}
return <EmptyProductList />;
}}
</Query>
</Layout>
)
As you can see in above code, load more function only called when flatlist is properly scrolled at the end.
I have a simple query auto-generated from aws AppSync, and I'm trying to use the Connect Component, with a FlatList and use a TextInput to filter and auto-update the list. But I confess I didn't found out a way to do that... any hints?
Tried to find more information about this without success...
Auto-Generated query:
export const listFood = `query ListFood(
$filter: ModelFoodFilterInput
$limit: Int
$nextToken: String
) {
listFood(filter: $filter, limit: $limit, nextToken: $nextToken) {
items {
id
name
description
...
My current code, which I don't quite know where to place my filter value:
<Connect query={graphqlOperation(queries.listFood)}>
{
( { data: { listFood }, loading, error } ) => {
if(error) return (<Text>Error</Text>);
if(loading || !listFood) return (<ActivityIndicator />);
return (
<FlatList
data={listFood.items}
renderItem={({item}) => {
return (
<View style={styles.hcontainer}>
<Image source={{uri:this.state.logoURL}}
style={styles.iconImage}
/>
<View style={styles.vcontainer}>
<Text style={styles.textH3}>{item.name}</Text>
<Text style={styles.textP}>{item.description}</Text>
</View>
</View>
);
}}
keyExtractor={(item, index) => item.id}
/>
);
}
}
</Connect>
What I aim is mainly to filter by item.name, refreshing the list while typing from a TextInput, probably going somewhere on the $filter variable...
Ok, I think I've figured out the usage with the AWS AppSync Out-of-the-box queries...
query MyFoodList{
listFood(
filter: {
name: {
contains:"a"
}
}
) {
items {
id
name
}
}
}
And it is finally working properly with this disposition on my react-native code:
<Connect query={ this.state.filter!=="" ?
graphqlOperation(queries.listFood, {
filter: {
name: {
contains: this.state.filter
}
}
})
:
graphqlOperation(queries.listFood)
}>
I still didn't manage to make the sort key work yet... will try a little more and open another topic for it if I didn't get anything...
This is filter in use in React / Javascript:
const [findPage, setFindPage] = useState('') // setup
async function findpoints() {
// find user & page if exists read record
try {
const todoData = await API.graphql(graphqlOperation(listActivitys, {filter : {owner: {eq: props.user}, page: {eq: action}}}))
const pageFound = todoData.data.listActivitys.items // get the data
console.log('pageFound 1', pageFound)
setFindPage(pageFound) // set to State
} catch (err) {
console.log(err)
}
}
The async / wait approach means the code will try to operate, and move on to other areas of your code putting data into findPage through setFindPage when and if it finds data
I'm trying to write a hacky fix to ScrollableTabView since it isn't playing nice with the function that triggers when there's a tab switch. When I replace the setState with console.log I see that it only triggers once with every tab switch so it's not looping infinitely like the error is complaining.
Parent container
state = {
headerName: 'Loading',
}
setHeader = (header) => {
this.setState({'headerName': header})
}
render () {
return (
<ScrollableTabView
renderTabBar={() => <BottomTabBar setHeader={this.setHeader} headerNames={['A','B','C']} />}
>
)
}
BottomTabBar
render() {
this.props.setHeader(this.props.headerNames[this.props.activeTab])
...
}
Attention: I have posted an answer down there, personally I think it's the best solution so far. Even though it's not the highest rated answer, but based on the result I'm getting, it is very efficient.
---------------------------------------------Original Question-------------------------------------------------------
Suppose I am writing a Twitter clone, but much simpler. I put each item in FlatList and render them.
To "like" a post, I press the "like" button on the post and the "like" button turns red, I press it again, it turns gray.
This is what I have so far: I store all the loaded posts in this.state, each post has a property called "liked", which is boolean, indicating whether this user has liked this post or not, when user presses "like", I go to state.posts and update the liked property of that post, and then use this.setState to update posts like so:
// 1. FlatList
<FlatList
...
data={this.state.posts}
renderItem={this.renderPost}
...
/>
// 2. renderPost
renderPost({ item, index }) {
return (
<View style={someStyle}>
... // display other properties of the post
// Then display the "like" button
<Icon
name='favorite'
size={25}
color={item.liked ? 'red' : 'gray'}
containerStyle={someStyle}
iconStyle={someStyle}
onPress={() => this.onLikePost({ item, index })}
/>
...
</View>
);
}
// 3. onLikePost
likePost({ item, index }) {
let { posts } = this.state;
let targetPost = posts[index];
// Flip the 'liked' property of the targetPost
targetPost.liked = !targetPost.liked;
// Then update targetPost in 'posts'
posts[index] = targetPost;
// Then reset the 'state.posts' property
this.setState({ posts });
}
This approach works, however, it is too slow. The color of the "like" button flips as I press it, but it usually takes about 1 second before the color changes. What I want is that the color would flip almost at the same time when I press it.
I do know why this would happen, I should probably not use this.setState, because when I do that, the posts state changed, and all posts get re-rendered, but what other approach can I try?
You can set extraData in FlatList:
<FlatList
...
extraData={this.state}
data={this.state.posts}
renderItem={this.renderPost}
...
/>
When state.posts or state.posts's item change, FlatList will re-render.
From FlatList#extradata:
A marker property for telling the list to re-render (since it implements PureComponent). If any of your renderItem, Header, Footer, etc. functions depend on anything outside of the data prop, stick it here and treat it immutably.
Update:
Functional component implementation:
export default function() {
// list of your data
const [list, setList] = React.useState([])
const [extraData, setExtraData] = React.useState(new Date())
// some update on the item of list[idx]
const someAction = (idx)=>{
list[idx].show = 1
setList(list)
setExtraData(new Date())
}
return (
<FlatList
// ...
data={list}
extraData={extraData}
/>
)
}
After updating list, I use setExtraData(new Date()) to tell the FlatList to re-render. Because the new time is different from the previous.
Don't get me wrong, #ShubhnikSingh's answer did help, but I retracted it because I found a better solution to this question, long time ago, and finally I remembered to post it here.
Suppose my post item contains these properties:
{
postId: "-L84e-aHwBedm1FHhcqv",
date: 1525566855,
message: "My Post",
uid: "52YgRFw4jWhYL5ulK11slBv7e583",
liked: false,
likeCount: 0,
commentCount: 0
}
Where liked represents whether the user viewing this post has liked this post, which will determine the color of the "like" button (by default, it's gray, but red if liked == true)
Here are the steps to recreate my solution: make "Post" a Component and render it in a FlatList. You can use React's PureComponent if you don't have any props that you pass to your Post such as an array or object that can be deceptively not shallow equal. If you don't know what that means, just use a regular Component and override shouldComponentUpdate as we do below.
class Post extends Component {
// This determines whether a rendered post should get updated
// Look at the states here, what could be changing as time goes by?
// Only 2 properties: "liked" and "likeCount", if the person seeing
// this post ever presses the "like" button
// This assumes that, unlike Twitter, updates do not come from other
// instances of the application in real time.
shouldComponentUpdate(nextProps, nextState) {
const { liked, likeCount } = nextProps
const { liked: oldLiked, likeCount: oldLikeCount } = this.props
// If "liked" or "likeCount" is different, then update
return liked !== oldLiked || likeCount !== oldLikeCount
}
render() {
return (
<View>
{/* ...render other properties */}
<TouchableOpacity
onPress={() => this.props.onPressLike(this.props.postId)}
>
<Icon name="heart" color={this.props.liked ? 'gray' : 'red'} />
</TouchableOpacity>
</View>
)
}
}
Then, create a PostList component that will be in charge of handling the logic for loading posts and handling like interactions:
class PostList extends Component {
/**
* As you can see, we are not storing "posts" as an array. Instead,
* we make it a JSON object. This allows us to access a post more concisely
* than if we stores posts as an array. For example:
*
* this.state.posts as an array
* findPost(postId) {
* return this.state.posts.find(post => post.id === postId)
* }
* findPost(postId) {
* return this.state.posts[postId]
* }
* a specific post by its "postId", you won't have to iterate
* through the whole array, you can just call "posts[postId]"
* to access it immediately:
* "posts": {
* "<post_id_1>": { "message": "", "uid": "", ... },
* "<post_id_2>": { "message": "", "uid": "", ... },
* "<post_id_3>": { "message": "", "uid": "", ... }
* }
* FlatList wants an array for its data property rather than an object,
* so we need to pass data={Object.values(this.state.posts)} rather than
* just data={this.state.posts} as one might expect.
*/
state = {
posts: {}
// Other states
}
renderItem = ({ item }) => {
const { date, message, uid, postId, other, props, here } = item
return (
<Post
date={date}
message={message}
uid={uid}
onPressLike={this.handleLikePost}
/>
)
}
handleLikePost = postId => {
let post = this.state.posts[postId]
const { liked, likeCount } = post
const newPost = {
...post,
liked: !liked,
likeCount: liked ? likeCount - 1 : likeCount + 1
}
this.setState({
posts: {
...this.state.posts,
[postId]: newPost
}
})
}
render() {
return (
<View style={{ flex: 1 }}>
<FlatList
data={Object.values(this.state.posts)}
renderItem={this.renderItem}
keyExtractor={({ item }) => item.postId}
/>
</View>
)
}
}
In summary:
1) Write a custom component (Post) for rendering each item in "FlatList"
2) Override the "shouldComponentUpdate" of the custom component (Post) function to tell the component when to update
Handle the "state of likes" in a parent component (PostList) and pass data down to each child
If you are testing on android than try turning off the developer mode. Or are you hitting some API and updating the post on the server and updating the like button in UI corresponding to the server response? If that is the case do tell me, I too have encountered this and I solved it. Also I have commented the second last line in your code which isn't needed.
// 1. FlatList
<FlatList
...
data={this.state.posts}
renderItem={this.renderPost}
...
/>
// 2. renderPost
renderPost({ item, index }) {
return (
<View style={someStyle}>
... // display other properties of the post
// Then display the "like" button
<Icon
name='favorite'
size={25}
color={item.liked ? 'red' : 'gray'}
containerStyle={someStyle}
iconStyle={someStyle}
onPress={() => this.onLikePost({ item, index })}
/>
...
</View>
);
}
// 3. onLikePost
likePost({ item, index }) {
let { posts } = this.state;
let targetPost = posts[index];
// Flip the 'liked' property of the targetPost
targetPost.liked = !targetPost.liked;
// Then update targetPost in 'posts'
// You probably don't need the following line.
// posts[index] = targetPost;
// Then reset the 'state.posts' property
this.setState({ posts });
}
I don't know how to pass a reference to the TripList instance below to the AddTrip component. I need to do something like that to signal to TripList to refresh the data after adding a new trip.
In my render() method, inside <Navigator> I have:
if (route.index === 1) {
return <TripList
title={route.title}
onForward={ () => {
navigator.push({
title: 'Add New Trip',
index: 2,
});
}}
onBack={() => {
if (route.index > 0) {
navigator.pop();
}
}}
/>
} else {
return <AddTrip
styles={tripStyles}
title={route.title}
onBack={() => { navigator.pop(); }}
/>
}
However, when I call onBack() in AddTrip, after adding a trip, I want to call refresh() on TripList so the new trip is displayed. How best can I structure things to do that? I'm guessing I need to pass TripList somehow to AddTrip and then I can call refresh() there easily right before calling onBack().
This is not how React works. You don't pass instances of a component around, rather you pass the data to your component via props. And your component AddTrip should receive another props which is a function to call when adding a trip.
Let me illustrate this with a code example, this is not how your code should be in the end, but it'll illustrate how to contain the data outside of your components.
// Placed at the top of the file, not in a class or function.
let allTrips = [];
// Your navigator code.
if (route.index === 1) {
return <TripList
trips={allTrips}
title={route.title}
onForward={ () => {
navigator.push({
title: 'Add New Trip',
index: 2,
});
}}
onBack={() => {
if (route.index > 0) {
navigator.pop();
}
}} />
} else {
return <AddTrip
styles={tripStyles}
title={route.title}
onAdd={(tripData) => {
allTrips = [...allTrips, tripData];
}}
onBack={() => { navigator.pop(); }} />
}
As you can see, the logic about adding and finding the trips comes from the parent component, which is the navigator in this case. You will also note that we are reconstructing the content of allTrips, this is important as React is based on the concept of immutability.
You must have heard of Redux which is a system allowing all your components to discuss with a global store from which you fetch and save all your application state. It's a bit more complex that's why I did not use it as an example it.
I'll almost forget the most important! You will not need to signal to to your component that it needs refreshing, the magic of React should take care of it by itself!