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.
Related
Good day SO.
I am a beginner in React Native so my terminology is very lacking. The project was inherited from previous programmer.
I have an async functions
getData = async () => {}
Then here:
componentDidMount() {
this.getData ();
}
Then last is Flatlist
<FlatList
data={this.state.somedata}
renderItem{({item, index}) => {}} />
My question is, if data is changed, how should I update my flatlist? I read that I need to add extraData but I dont know what variable should I add inside.
Note I know that componentDidMount only runs once on the first render. But I dont know how to proceed.
I have a Stack.Navigator, when I navigate to a page that contains my FlatList which renders 4x6 items at once, all of the other components will render and the flatlist will be invisible/not rendered. The app then locks up, and then after that the flatlist renders all the items and the layout is bumped around which is not desirable. Is this expected behaviour and what can I do about it? I'd prefer the whole app freeze/stutter until all of the first page is ready to show at once, rather than rendering everything but the Flatlist and then bumping the UI around.
The FlatList component is very uncontroversial as far as I can see.
<View>
<FlatList
numColumns={4}
columnWrapperStyle={styles.colWrap}
keyExtractor={(theitem) => theitem.id}
renderItem={renderIndividualSound(onSoundButtonPress)}
data={soundPage}
key="soundspage"
/>
</View>
Upon further inspection, I was using a useState() hook that init'd with a blank array, and then using a useEffect(()=>{}, []) hook to update the state once at initialisation, meaning a blank list was passed through for the very first render.
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).
I have a large long image with a few inputs at the bottom in my react native view. When the view loads I want it to be "scrolled" to the bottom of the page -- all the examples I can find online are triggered because of some event that the user does.
I want to call scrollToEnd() but I'm not sure where in the lifecycle the ref will actually be set -- anyone have ideas?
Use scrollToEnd this way. It will take to the bottom of ScrollView
<ScrollView
ref={ref => this.scrollView = ref}
onContentSizeChange={(contentWidth, contentHeight)=>{
this.scrollView.scrollToEnd({animated: true});
}}>
I am not clear with your question but
With react-native Image component we have onLoad prop. I think this is what you are looking for.
try something like:
<Image source={{uri...}} onLoad={(e)=>this.handleImageLoaded(e)}/>
then inside handleImageLoaded method you can use scrollToEnd() with some ref as per your code.
also there are other useful props like onLoadStart/End check here
https://facebook.github.io/react-native/docs/image
Or if you are just waiting for the view to render then to scroll
for that I think componentDidAppear() lifecycle method, if using react-native -navigation by wix
or with react-navigation
willFocus, willBlur, didFocus and didBlur events for the component render cycle.. explained here
https://reactnavigation.org/docs/en/navigation-prop.html#addlistener-subscribe-to-updates-to-navigation-lifecycle
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>