i have two screens one where the profile information is showing and another screen to edit the information. If i entered the first screen profile it's shows me the right data from the database. Then i move to the next screen where i can change the Information everthing worked so far. But if I go back to the previous screen i still see the old data. So there is no rerendering.
But if i navigate to the other screen that screen fetched the new data. and the call getCurrentUserProfile is executed
This ist the screen with the profile information about the user.
const ProfileScreen = props => {
const [userObj, setUserObj] = useState({});
useEffect(() => {
let mounted = true;
getCurrentUserProfile().then(user => {
if (mounted) {
setUserObj(user);
}
console.log(user)
});
return () => mounted = false;
}, []);
console.log("----b------") // This is only output on the first call
}
How can i fix this. Is there a way when in the database is something changed, so the component rerender and fetches the new data.
Thanks.
You are probably using #react-navigation package. So, if you want to refetch data when come back to the previous page, you can use https://reactnavigation.org/docs/use-is-focused on that “previous” page.
Just look at their docs, you will get the idea.
P.S: Usually we don't unmount components directly. In React Native, we use navigator to mount/unmount components
Related
I have implemented react native tab navigator and added 4 screens to it.
I post some record to api in the second screen and i want to have the updated record in the 4th screens where i am getting updated records..
Useeffect only gets targeted only once, and when i put something in it's argument it gives me strange behavior.
I want useeffect to reload and call the api to get latest items in the 4th screen without putting anything in it's arguement(empty argument)
Any help would be highly appreciated.
Try doing this ;
useEffect(() => {
const unsubscribe = navigation.addListener("focus", () => {
makeApiCall();
});
return unsubscribe;
}, [navigation]);
Get navigation in component's arguments(destructuring)
like below;
const My4thTab = ({ navigation }) => {
}
This way useEffect will trigger only once, every time you come on this screen
but make sure to clear the previous state where you store your data, otherwise, there could be a record duplication.
Hope it helps :)
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.
My RN 0.62.2 app needs to automatically save page data just before the function component unmounts. The idea is that when the user close the page (detecting losing focus may not work here since user may zoom in image in modal screen), then the save (to backend server) is automatically triggered. Since it is function component, how to know when the component will unmount?
Here is the sample code of a function component shall do:
const MyCom = () => {
//do something here. ex, open gallery to upload image, zoon in image in `modal screen, enter input`
if (component will unmount) {
//save the data by sending them to backend server
}
}
The useEffect triggers with every rendering and will have performance issue if keep saving to backend server with each and every rendering. The auto save only happens once just before the component unmount. User may click Back or Home button to leave the page.
Yoı must use useEffect for componentWillUnmount in functional components.
const MyCom = () => {
//do something here. ex, open gallery to upload image, zoon in image in
useEffect(() => {
// Component Did Mount
return => {
// ComponentWillUnmount
}
},[])
return(/*Component*/)
}
I am new to React Native
I am trying to create a multiselect view where user can select and deselect the items and then the selected items should pass back to the previous container and when user comes back to the next view the selected items should be checked.
I am trying to implement but getting the issue it is not updating data accurately. It shows only 1 selected item when I came back again to the screen.
Can anyone tell me the best way to do that or if there is any tutorial.
Should I do it with Redux or using react native?
Any help would be appreciated!!
Thanks!!
I believe the issue you describe is due to the following:
In componentDidMount you are calling updateItemWithSelected in a loop. This updateItemWithSelected call is both overwriting the checked attributes for all of the arrayHolder values on each call and also not using the updater function version of setState, so the later call of the loop may overwrite the earlier calls since setState is async and batched. If you are not using updateItemWithSelected elsewhere you should simplify componentDidMount to:
componentDidMount() {
const selectedTitles = {};
const { state } = this.props.navigation
const params = state.params || {};
if (params.data.length){
params.data.forEach((element) => {
// create a map of selected titles
selectedTitles[element.title] = true;
})
}
const arrayHolder = this.array.map(item => {
// map over `this.array` and set `checked` if title is in `selectedTitles`
return {...item, checked: !!selectedTitles[item.title]};
});
this.setState({ arrayHolder });
}
and delete updateItemWithSelected.
I'm developing a react-native / redux app with a bottom-tab-navigator similar to the example at https://reactnavigation.org/docs/en/tab-based-navigation.html#customizing-the-appearance. My screens all connect to a Redux store and display shared data, however I'd like at least one of these screens to ignore the current data in the store and instead re-initialize this data each time it's navigated to (instead of continuing to display the data in whatever state it was last left in).
The screen has a method to do this, but I can't figure out how to call it after the first time the screen is rendered (e.g. from the constructor or componentDidMount() method). I can't call it from the render() method as this causes a "Cannot update during an existing state transition" error.
I need my navigator to somehow cause my HomeScreen.initializeData() method to be invoked each time the Home icon is pressed, but how do I do this?
HomeScreen.js:
initializeData() {
this.props.resetData(initialValue);
}
const initialValue = ...
(resetData() is a dispatch function that re-initializes the Redux store).
Updating state from render() would create an infinite loop. Also, you don’t want to run your state update every time the component re-render, only when the tab button is pressed. This tells me that the proper place to make your state update is some onPress function on the tab button.
So the question now relies on how to implement some onPress function on a tab button. I believe this answer this question:
Is there an onPress for TabNavigator tab in react-navigation?
So I found an answer, it's a little more complicated than might be expected: As Vinicius has pointed out I need to use the tabBarOnPress navigation option, but I also need to make my dispatch function available to this navigation option.
To do this I found I need to pass a reference to my dispatch function (which is available as a property of my screen) into the navigation option, so I've used navigation params to do this and here's what I've ended up with:
HomeScreen.js:
componentDidMount() {
initializeData(this.props);
this.props.navigation.setParams({ homeProps: this.props });
}
export const initializeData = (homeProps) => {
homeProps.resetData(initialValue);
};
const initialValue = ...
AppNavigator.js:
tabBarOnPress: ({navigation, defaultHandler}) => {
const routeName = navigation.state.routeName;
if (navigation.state.params === undefined) {
// no params available
} else if (routeName === 'Home') {
let homeProps = navigation.getParam('homeProps', null);
initializeData(homeProps);
} else if (routeName === ...
...
}
defaultHandler();
}
Notes:
I'm passing props as a navigation param rather than my dispatch function (which also works) as it's more flexible (e.g. it makes all of my dispatch functions available).
initializeData() is called both during construction of HomeScreen (for the first time the screen is displayed) and from the navigation icon (for subsequent displays of the screen).
It's necessary to check that params is defined within the navigation option as it'll be undefined the first time the screen is displayed (as screen construction has yet to occur). This also makes it necessary to call initializeData() during screen construction.