I'd like to add a SectionList to my app such that it renders to a specific section (that isn't the first section in the list). Calling scrollToLocation on componentDidMount does not work; however, adding a button that calls scrollToLocation does. Is there a reason for this?
Could this be due to the SectionList reference (I've tried a few approaches for assigning reference, e.g. variable assignment, function assignment, using createRef, etc.)?
Here is a link to a stripped-down Expo snack to illustrate what I mean: https://snack.expo.io/#bobbymoogs/scrolltolocation-on-componentdidmount.
I found the best solution on this thread is to use onLayout to trigger the scroll:
scrollToInitialPosition = () => {
this.scrollViewRef.scrollTo({ y: 100 });
}
...
<ScrollView
ref={(ref) => { this.scrollViewRef = ref; }}
onLayout={this.scrollToInitialPosition}
/>
Note there are lots of other suggestions using setTimeout, componentDidUpdate, InteractionManager, etc. However using onLayout was the only one that worked for me (and also seems to me to be the cleanest).
Related
I am using a react native with expo. I have a lot of videos that I need to render (sort of like TikTok does). When I fetch about 30 videos and put them in the flat list in the renderItem method, it gets stuck and luggish. I was thinking about getting an amount of videos but sending to the renderItem method only 3 videos each time, and when the user will scroll down and reach index 2 it will shift the first index and append the fourth video from the fetched one. The idea was to have a small array of size 3 and change the items in it every scroll, in order to prevent rendering all the videos at once. That required array manipulation and caused a rerender each time the array of videos was updated(each change made sort of a flash - what was indicating a whole rerender).
My question is how should it be implemented in order the transition between the videos to be as fast and clean as possible from the client side perspective? What is the correct way to render videos in a flat list so it won't be stuck? I dont think It should be done that way, there has to be a better way.
This is what I have tried:
// challenges is an array coming from a fetch, just sliced it for the purpose of the example
// suppose it is an array that contains 30 items
const [currentVideos, setCurrentVideos] = useState([challenges.slice(0,3)]);
<FlatList
data={currentVideos}
renderItem={renderItem}
keyExtractor={(challenge, i) => challenge._id}
showsVerticalScrollIndicator={false}
snapToInterval={Dimensions.get("window").height - UIConsts.bottomNavbarHeight}
snapToAlignment={"start"}
decelerationRate={"fast"}
ref={(ref) => {
flatListRef.current = ref;
}}
onScrollToIndexFailed={() => alert("no such index")}
onViewableItemsChanged={onViewRef.current}
onScrollEndDrag={() => (scrollEnded.current = true)}
onScrollBeginDrag={beginDarg}
></FlatList>
useEffect(() => {
// just wanted to check on 3 videos
if (currentlyPlaying === 2) {
let temp = currentVideos;
temp.shift(); // pop the top item
temp.push(challenges[4]) // append a new one
setCurrentVideos(temp);
}
}, [currentlyPlaying]);
const onViewRef = useRef(({ viewableItems }) => {
// change playing video only after user stop dragging
scrollEnded.current && setCurrentlyPlaying(viewableItems[0]?.index);
});
I would avoid manipulating the data array and doing business logic inside of the component.
Besides, you can achieve your desired behaviour without the need to manipulate your data array at all, with the maxToRenderPerBatch FlatList prop. As mentioned in the official RN docs for FlatList optimization techniques.
You should avoid using anonymous functions and objects inside of your component's properties, move them outside of the return statement and use the useMemo and useCallback hooks to avoid their unnecessary recreation on every re-render. For example instead of writing your code like this:
const App = () => {
return (
<FlatList
keyExtractor={(challenge, i) => challenge._id}
snapToInterval={Dimensions.get('window').height - UIConsts.bottomNavbarHeight}
/>
);
};
A better approach would be to re-write it to something like this:
const App = () => {
// Because of useCallback, the keyExtractor function will be memoized and won't recreate itself on every re-render
const keyExtractor = useCallback((challenge, i) => challenge._id, []);
// useMemo is almost the same as useCallback, but it is used to return non-function types
// Defining your snapToInterval variable like this will cause it to memoize its value and it
// won't recreate itself on every re-render
const snapToInterval = useMemo(() => Dimensions.get('window').height - UIConsts.bottomNavbarHeight, []);
return (
<FlatList
keyExtractor={keyExtractor}
snapToInterval={snapToInterval}
/>
);
};
If you haven't already, you should consider extracting the component returned from the renderItem function to a different file and applying React.memo to it.
Note: try not to overuse useCallback and useMemo. You can find good and detailed explanation of why not to overuse them here and here.
If you're able to, you should optimize your videos before uploading them to the server. You can optimize your client side part of the app as much as you want, but if the content isn't properly optimized, you won't be able to achieve a smooth and performant experience regardless of your efforts.
Here's also some articles describing how you can optimize your FlatList component:
How did I optimize my React Native FlatList?
8 ways to optimize React native FlatList performance
Optimizing a React Native FlatList With Many Child Components
React Native Performance Optimisation With Hooks
React Native: Optimized FlatList of videos
I hope that some of this will be helpful to you. Good luck.
I have been searching for a solution as well. I have worked out a solution based on some previous work using InViewPort. you can check it out here https://github.com/471Q/React-Native-FlatList-Video-Feed
I have FlatList in render() function with a reference,
<FlatList
ref={(ref) => { this.flatListRef = ref }}
data={this.state.data}
renderItem={({ item, index }) => this.renderOuterCard(item, index)}
/>
I need to use this.flatListRef to call FlatList's methods, which is possible only when FlatList is rendered. Otherwise following error occurs,
Cannot read the property 'ScrollToIndex' of undefined
(I tried to call FlatList's ScrollTOIndex method)
Infact I called ScrollTOIndex in componentDidMount() method , But still this error occurs. Hence, This is clear that componentDidMount() is called before render() finishes completely.
Can anybody let me know when rendering finishes exactly?
This is clear that componentDidMount() is called before render() finishes completely.
According to this schema the first render phase occur before componentDidMount.
http://projects.wojtekmaj.pl/react-lifecycle-methods-diagram/
Live example:
https://snack.expo.io/#flexbox/flatlist-with-state-example
I am having the same issue. I do have a Component that uses FlatList and I would like to know when, within the first render, the list has rendered the visible items (ready state).
I have discovered that on the main component the componentDidMount was triggered because the FlatList component have mounted as well. And because FlatList Component asyncronously renders each item they only show up after on componentDidUpdate.
I have struggled for a while and even with the componentDidUpdate approach I could only get the moment where FlatList got new data (not rendered the items).
So I found out that I could intercept the renderItem method to create some logic to better estimate what and when is being rendered. The other option was to have a setTimeout (very hacky) to trigger the work based on a average time (very poor solution).
If someone have a proper approach to be able to know when the FlatList finishes rendering the inView items please share.
Thanks.
I know that the practice of react native is to use onChangeText for change value as follow.
<TextInput
onChangeText = {(text)=> this.setState({myText: text})}
value = {this.state.myText}
/>
However, I wonder if i could do something like this. To summarise, I want to loop through all the TextInput and get the ref and value. I just want to do things in javascript way as follow. Is that possible to be done?
<TextInput id="id1" ref={ref => (this.remark = ref)} />
<TextInput id="id2" ref={ref => (this.remark1 = ref)} />
onSubmit = () => {
forEach(TextInput in component) {
console.log(TextInput.id) <- note id is custom property
console.log(TextInput.refName)
console.log(TextInput.value)
}
}
Yes, but I wouldn't recommend this approach. You could simply create an array of refs and loop through it in your onSubmit function.
forEach(TextInput in component) {
This is not possible in any javascript environment (not only because forEach and for..in syntax is different but also you can't expect to be able to loop over component elements by type (?) and get them)
What you want to do is not javascript way but old style browser way:
there are no ids in react-native
technically you could get uncontrolled TextInput's value like you would do in plain react in browser environment (via this.textInputRef._lastNativeText) but it's discouraged in react-native, most likely because because instead of DOM react native has to render to native views which all differ depending on the platform (iOS, Android, Windows, etc) but have to work the same
So it's not only impossible in react native but in plain react as well. It looks to me like you want to create a form, and sooner or later you will find out that you want validation or transformation on your inputs and switch back to controlled components anyway
What does this mean?
This happens when I update a list of iterated views something like
<View style={{ flexDirection: 'row', padding: 20, backgroundColor: '#fff' }}>
<Ionicons name={jobIcon} color={theme.iconColor} size={30} />
<Text>{jobService}</Text>
<Text>{jobDate}</Text>
</View>
mapped inside a scrollview.
this error pops up when I modify the array from child scene.
scene1 - is where the ScrollView with job list array of views
sence2 - is where I delete a job and should update scene1 when I do remove a job
If you want the LayoutAnimation to work with ScrollView, replace
LayoutAnimation.configureNext(LayoutAnimation.Presets.easeInEaseOut)
with
LayoutAnimation.configureNext({
duration: 300,
create:
{
type: LayoutAnimation.Types.easeInEaseOut,
property: LayoutAnimation.Properties.opacity,
},
update:
{
type: LayoutAnimation.Types.easeInEaseOut,
}
});
This works on both Android and iOS without any crashes.
In my case I was using LayoutAnimation for my ScrollView. Inside it a map of Items. When an Item is removed from the list this happens. Not using LayoutAnimation seems to be working fine.
It's happening when you call layout animation when it already in process. iOS will show an warning while Android will explode with this error.
You can use this easy pattern to fix it when you're using LayoutAnimation from same component.
layoutAnimation() {
if (!this.layoutAnimationActive) {
this.layoutAnimationActive = true;
LayoutAnimation.configureNext(LayoutAnimation.Presets.easeInOut, () => { this.layoutAnimationActive = false; });
}
}
This happens when a component only has x amount of children, but you are trying to remove a child with index greater than x. Like an index out of bounds exception that is common with arrays. Can cause lots of frustration because often times the child you are trying to remove DOES INFACT EXIST. But might be happening because you are using a third party component that only expects a certain amount of children.
For me, it happened when I put an extra child into air-bnb MapView. I fixed the issue by making this element the child of it's grandparent (it was absolutely positioned so it didn't affect styling).
I encountered this issue when creating a react-native application using Expo.
This error was often getting raised when I was rendering new Markers onto a Map (which was rendered via a MapView component).
What fixed the issue for me was to add a key prop to the Marker component e.g.
<Marker coordinate={coordinate} key={`${coordinate.latitude}_${coordinate.longitude}`} />
Hope this helps anyone who also encounters this issue when dealing with MapView and Marker components!
In my case, I was deleting an item in a virtualized list. I was using redux to manage the data of the list and updated the list with the new data. However, the component for the item that was deleted caused this error.
I solved this by adding a boolean state property on this item component, example "hideItem". My item was a class component but a setState hook could also be used for a functional component. I set this to true after deletion. The post hid with layout animation correctly, and when the page refreshed it no longer rendered the deleted item. Hence, the error went away on android without needing to not use LayoutAnimation.
Evidently, it seems this bug can show its ugly face in various conditions. After a couple of hours of debugging, I found my root cause to be a key prop being passed to a component that didn't require it. I'm still unsure of why this was causing a crash, however, I suspect it has to do with the fact that the component accepts the key as a unique way to identify the view, but was also using the componentWillReceiveProps(props: *) lifecycle method that updated the component's state.
This is likely to happen if you're using some native components, where some ViewManager returns a LayoutShadowNode in createShadowNodeInstance of ViewGroupManager or something extending ReactShadowNode in createShadowNodeInstance of ViewManager on Android, and a RCTShadowView in the shadowView method of RCTViewManager on iOS. But, returns null/nil for some other View in some other ViewManager.
Then, if you combine children of both types in the same parent, and any of the elements without shadowViews/Nodes come before the changing number of elements which do have shadowViews/Nodes, then the indices won't match up, and the RCTUIManager on iOS and NativeViewHierarchyManager on Android will choke and produce these exceptions.
I solved a similar issue in react-native-svg recently, by making all the ViewManagers return values rather than null/nil. https://github.com/facebook/react-native/issues/23350
So, try upgrading react-native-svg to v9.2.4 and the issue might be fixed. Or, try moving the IonIcons to the end of your children.
I had the same issue, because I had an Array.map inside a condition which I was updating using LayoutAnimation.
I fixed it by moving the state variable inside the map function.
I am using vitalized flatlist with swipe left right delete option, and when list is more than 200 items and I use LayoutAnimation then the above problem comes out on arbitrary based, I figured out that deleted item still exist because of LayoutAnimation so you can play around with timings of update using the following code
LayoutAnimation.configureNext({
duration: 300,
create:
{
duration:500
type: LayoutAnimation.Types.easeInEaseOut,
property: LayoutAnimation.Properties.opacity,
},
update:
{
duration: 500,
type: LayoutAnimation.Types.easeInEaseOut,
}
});
this.refs['task'].setNativeProps({
style: {transform: [{translateX: Dimensions.get('window').width}]},
});
one more thing, I am also hiding the item suddenly after it's deletion occurs
here is code snippet
this.props.handleDeleteTask(this.props.item.id);
this.setState({hideItem:true}) // here I am hiding through state function, so the item should disappear right after it's deletion.
How do you re-run React Component Lifecycle methods to determine if a re-render is necessary when transitioning back to previous screens from stack using React Native Router Flux?
Scenario: Scene A -> B -> A
Lets say, A is the initial scene and we navigate from A to B with a push i.e Actions.SceneB. From B to A with a Pop. When the stack is popped to show Scene-A, none of the React Component methods are called for Scene-A. How do I determine if a re-render is necessary? I searched the Issues listed on the github repo and many seems to have this problem without a solution. How is this problem addressed?
I have the ugly work around of calling Actions.refresh() with a setTimeout.
Work Around that works!
This workaround seems to be hacky. There must be a better way to hook into component lifecycle to determine if a re-render is required. Perhaps a callback into the Component?
<TouchableHighlight underlayColor='#efefef' onPress={() => { Actions.pop(); setTimeout(()=> Actions.refresh(), 500)}} style={styles.cancel}>
Options that do not work
Actions.pop({type: 'reset'})
OR
Actions.refresh({"key" : "sceneA"})
Work Around that works! This workaround seems to be hacky. There must be a better way to hook into component lifecycle to determine if a re-render is required.
<TouchableHighlight underlayColor='#efefef' onPress={() => { Actions.pop(); setTimeout(()=> Actions.refresh(), 500)}} style={styles.cancel}>
This will call shouldComponentUpdate() method which gives an option to determine, if a re-render is required.
I was facing the same issue below code gave me required result.
let count = 0;
moveToMainScreen = () => {
count += 1;
Actions.pop({ refresh: { test: count } });
};
<Button onPress={this.moveToMainScreen}> Click </Button>