TL;DR: My UI freezes for .5-1s when I try to render a component that does a API fetch within a useEffect().
I have ComponentX which is a component that fetches data from an API in a useEffect() via a redux dispatch. I'm using RTK to build my redux store.
function ComponentX() {
const dispatch = useAppDispatch();
useEffect(() => {
dispatch(fetchListData()); // fetch list data is a redux thunk.
}, [dispatch]);
...
return <FlatList data={data} /> // pseudo code
}
as you can see the fetch will happen everytime the component is rendered.
Now I have ComponentX in App along with another component called ComponentY.
Here's a rudamentary implementation on how my app determines which component to show. Pretend each component has a button that executes the onClick
function App() {
const [componentToRender, setComponentToRender] = useState("x");
if (componentToRender === "x") {
return <ComponentX onClick={() => setComponentToRender("y")}/>
} else {
return <ComponentY onClick={() => setComponentToRender("x")}/>
}
}
Now the issue happens when I try to move from ComponentY to ComponentX. When I click the "back" button on ComponentY the UI will freeze for .5-1s then show ComponentX. Removing the dispatch(fetchListData()); from the useEffect fixes the issue but obviously I can't do that since I need the data from the API.
Another fascinating thing is that I tried wrapping the dispatch in an if statement assuming that it would prevent a data fetch thus resolving the "lag" when shouldReload is false. The UI still froze before rendering ComponentX.
useEffect(() => {
if (shouldReload) { // assume this is false
console.log("reloading");
dispatch(fetchListData());
}
}, [dispatch, shouldReload]);
Any idea what's going on here?
EDIT:
I've done a little more pruning of code trying to simplify things. What I found that removing redux from the equation fixes the issue. By simply doing below, the lag disappears. This leads me to believe it has something to do with Redux/RTK.
const [listData, setListData] = useState([]);
useEffect(() => {
getListData().then(setListData)
}, []);
Sometimes running the code after interactions/animations completed solves the issue.
useEffect(() => {
InteractionManager.runAfterInteractions(() => {
dispatch(fetchListData());
});
}, [dispatch]);
Related
I want to create an observable from a change event that gets fired on a React Native TextInput component. TextInput comes with 2 change props that I'm aware of (onChangeText and onChange). From what I gather, you need to use onChange if you want access to the native event you need to use onChange.
I don't know much about the native event object. I am trying to create an rxjs observable using fromEvent.
First I created a ref in my functional component like this:
const sqftRef = useRef().current
Then I attached this ref to the TextInput component like this:
<TextInput
ref={sqftRef} // attach a ref
label='Sqft'
mode='flat'
textContentType='none'
autoCapitalize='none'
keyboardType='numeric'
autoCorrect={false}
value={String(formValues.sqft)}
dense
underlineColor={colors.colorOffWhite}
onChangeText={(text) => setText(text)}
onChange={e => {
// somehow create an observable from this event ???
}}
style={styles.inputStyles}
theme={inputTheme}
/>
I tried to create an Observable using fromEvent like this but it doesn't work. I get undefined is not an object (evaluating target.addEventListener):
fromEvent(sqftRef, 'onChange').subscribe(value => console.log(value))
I know my approach is all wrong. Hoping someone can point me in the correct direction.
I would emit events you need into a subject, then subscribe to the subject in other parts of your code.
Here's a simple React example that should get you started
function App() {
const textChange = new Subject<string>();
useEffect(() => {
// subscribe to
const subscription = textChange.asObservable().subscribe(console.log)
return () => subscription.unsubscribe()
}, [])
// Emit events with a subject
return <textarea onChange={(e) => {
textChange.next(e.target.value)
}}>
</textarea>
}
render(<App />, document.getElementById('root'));
Check out the example here: https://stackblitz.com/edit/react-ts-akoyfv
I think the problem is with assigning the current directly to the sqftRef. Try to define it without current, but use current when creating the Observable, like the following:
const sqftRef = useRef();
Then create the Observable within useEffect to make sure that the DOM is ready:
useEffect(() => {
fromEvent(sqftRef.current, 'onChange').subscribe((value) =>
console.log(value)
);
});
OK, I was able to figure it out with the help of Amer Yousuf and Alex Fallenstedt.
I did something similar to what Alex suggested, modifying his solution for React Native. One reason his solution wasn't working for me is that it is important to use the useRef hook to prevent the Observable from being re-created on each render. If the observable is recreated (on a re-render) and useEffect doesn't run again, then we won't have an active subscription to the newly (re-created) observable (useEffect never runs again). That's why my call to sqft$.next was originally only being called once (the first time until we re-render).
My solution looks like this:
let sqft$ = useRef(new BehaviorSubject(0)).current
useEffect(() => {
const sub = sqft$.subscribe({
next: (val) => {
// just testing stuff out here
updateForm('sqft', val)
updateForm('lot', val * 2)
}
})
// this is only relevant to my use case
if (activeReport) sqft$.next(activeReport.sqft)
return () => sub.unsubscribe()
}, [activeReport])
and of course I call this in onChangeText:
onChangeText={(text) => {
sqft$.next(text)
}}
So this is working right now. I still feel like there may be a better way using onChange(e => ...stuff). I will leave this question open for a little bit in case anyone can break down how to do this using nativeEvent or explain to me how I can access an event off the TextInput component.
I have an async function and a useEffect that fetches data once.
const [data, setData] = useState([]);
async function fetchData() {
fetch(`${baseURL}api/v1/data/${userId}`)
.then((response) => response.json())
.then((response) => {
try {
if (response.length > 0) {
setData(response);
} else {
setData([]);
// console.log(response);
}
} catch (err) {
console.log('no response');
alert(err);
}
});
}
useEffect(() => {
fetchData();
}, [userId, data]);
I could remove the array on the use effect but it will always run the function if I do that.
So when I open the screen, it will fetch the latest data. However, if I want to add a new data from a different screen, it wont trigger the async nor the useEffect function. How should I tell RN that there is a new data? Would AsyncStorage work? to update a data from one screen and apply the data here? I am open for suggestions on how to proceed.
What I meant by a different screen: A register screen and a view screen. In this case, I already opened the View Screen before I open the register screen so view screen is already rendered.
In React Navigation and most of the navigation libraries, screens don't get unmounted from the stack when it's navigated to another screen. For example if you have a list of something and then you press to "+" button to navigate to the "new item" screen to add a new one, when you press back button, since the previous "list" screen was not unmounted from the stack, useEffect won't be triggered, and you won't get the new data.
There are a couple of solutions for this case:
You can hold your data in a global state, and when you update an item from another screen, after a successful API call, you can also update the global state. You can look for React Context, MobX or Redux for this.
You can pass parent's state with a callback from one screen to another if they are not that apart from each other. So that in the "new data" screen, you can call that callback function to change the parent screen's state too.
Third, and IMO the best way is using a hook called useFocusEffect by React Navigation itself: https://reactnavigation.org/docs/use-focus-effect
I hope these will help.
I am trying to show some dynamic content in my component but somehow useEffect causes a infinite loop.
What can be the problem?
useEffect(() => {
retrieveLocalData('following').then((contacts) => {
setLocalData(JSON.parse(contacts));
});
}, [getLocalData]);
async function retrieveLocalData(key) {
try {
return await AsyncStorage.getItem(key);
} catch (error) {
console.log(error);
}
}
console.log('test'); // infinite
Code: https://codepen.io/eneskul/pen/OJWEgmw
Updated Answer
The infinite loop is a result of the useEffect hook updating the same value that is triggering the hook to run in the first place.
Here's a simple example to illustrate the problem:
const [value, setValue] = useState({ foo: 'bar' });
useEffect(() => {
Promise.resolve('{"foo":"bar"}').then((result) => {
const newValue = JSON.parse(result);
// `newValue` is a new object, even if its content is identical to `value`.
setValue(newValue);
});
}, [value]);
In this example, when value is set, it causes the useEffect hook to execute, which will asynchronously update value with a new object, which will cause the useEffect hook to execute again, and so on. Even though the contents of the objects are identical, the JSON.parse call creates a new object with a new reference.
You can prevent the infinite loop by doing a deep equality check of the two objects before updating the state. Using something like Lodash's isEqual function makes this pretty easy.
useEffect(() => {
Promise.resolve('{"foo":"bar"}').then((result) => {
setValue((prev) => {
const newValue = JSON.parse(result);
// Do a deep comparison and only update state with new object if content is different.
return isEqual(prev, newValue) ? prev : newValue;
});
});
}, [value]);
In this example, the reference to value will only change if the contents of the objects are different.
However, this only explains what the problem is. I'm not sure what the right solution is for your problem, since it's not clear why the component only needs to load data from local storage into state when the state changes, but the state is only updated when it loads from local storage. There seems to be a "chicken or the egg" problem here. It feels like there should be something else that should trigger loading data from local storage into state, other than the data that was just loaded from local storage into state.
Previous Answer
The likely culprit here is getLocalData in the dependency list of the useEffect hook. If that is not a stable reference (i.e. the reference changes on each render), then it will cause the useEffect hook to execute, which will then trigger a state update, which will trigger a render, which will cause useEffect to execute again, which starts the whole thing over again.
In the sample code, it's not clear where getLocalData comes from. Wherever it comes from, you might consider wrapping it with the useCallback hook to create a stable reference. If it's just a typo and meant to be retrieveLocalData, then that is definitely the issue. Because retrieveLocalData is declared inside the component's render function, it will create a new instance of the function (with a new reference) on each render.
I would just move it inside the useEffect hook and eliminate the dependencies.
useEffect(() => {
AsyncStorage.getItem('following')
.then((contacts) => {
setLocalData(JSON.parse(contacts));
})
.catch((error) => {
console.log(error);
});
}, []);
I am using React Native with functional components. componentDidMount() etc. are not available in functional components, instead I use Hooks. But Hooks don't act like lifecycle methods. I am wondering what the best practices are.
Assumed that we have a function like this one:
const ABCScreen = () => {
const [someHook, setSomeHook] = useState<any>()
useEffect(() => {
// some code inside this function which is called on every component update
}, [])
server.asyncCall().then(data => {
setSomeHook(data)
})
return (<View>
{someHook ? (<Text> `someHook` was assigned </Text>) : (<Text> `someHook` was not assigned, display some ActivityIndicator instead</Text>)}
</View>)
}
Where to place server.asyncCall()? Inside or outside of useEffect?
I think you have a misunderstanding here. The convention is that all the fetching data is going to be placed inside the componentDidMount lifecycle method. React useEffect hook can replace this easily by placing an empty array of dependencies, which means you can place that call inside the useEffect you already have.
Unlike you mention in your code comment, this hook won't be triggered on each component update. It will be only be triggered once the component is being mounted. So, you should be able to do it as follows:
const ABCScreen = () => {
const [someHook, setSomeHook] = useState<any>()
useEffect(() => {
server.asyncCall().then(setSomeHook)
}, [])//only triggered when component is mounted.
In the future, you might want to check the rules of the hooks.
I'm working on porting an app to React-Native to test it out. When I pop back to a previous view in the navigator stack (hit the back button) I'd like to run some code. Is there a viewWillAppear method? I see on the Navigator there is a "onDidFocus()" callback which sounds like it might be the right thing.. but there doesn't appear to be anything like that on NavigatorIOS
I find a way to simulate viewDidAppear and viewDidDisappear in UIKit,
but i'm not sure if it's a "right" way.
componentDidMount: function() {
// your code here
var currentRoute = this.props.navigator.navigationContext.currentRoute;
this.props.navigator.navigationContext.addListener('didfocus', (event) => {
//didfocus emit in componentDidMount
if (currentRoute === event.data.route) {
console.log("me didAppear");
} else {
console.log("me didDisappear, other didAppear");
}
console.log(event.data.route);
});
},
For people who are using hooks and react navigation version 5.x, I think you can do this to expect similar behavior of viewDidAppear:
import React, {useCallback } from "react";
import { useFocusEffect } from "#react-navigation/native";
const SomeComponent = () => {
useFocusEffect(
useCallback(() => {
//View did appear
}, [])
);
//Other codes
}
For more information, refer https://reactnavigation.org/docs/use-focus-effect/
Here is a solution to simulate viewDidAppear with latest React Navigation version:
componentDidMount() {
var currentRoute = this.props.navigation.state.routeName;
this.props.navigation.addListener('didFocus', (event) => {
if (currentRoute === event.state.routeName) {
// VIEW DID APPEAR
}
});
}
Thanks Jichao Wu for the idea :)
If you are using React Navigation, use this:
componentDidMount(){
this.props.navigation.addListener('focus', () => {
// put your code here
});
}
Basically you are adding a focus event when component is first mounted. It will be called whenever (including the first time too) the component is focused. Ideally you'd also need to remove listener on unmount by capturing the value returned from addListener call and call that returned value (which is actually the unsubscribe function).
I've created a custom button with onLeftButtonPress to handled the back to run code as per https://github.com/facebook/react-native/issues/26
The way to get around it is to either set your custom back button on the left side, or to implement - viewWillDisappear: in iOS.
You can use ComponentWillMount or if you're leaving the view you can use ComponentWillUnmount which will run some code on exit.