I've tried a lot of answers given to similar questions but nothing is fixing my problem as I'm changing the state in a function which I'm calling on the press of a button in a third-part library I'm using.
I'm using react-native-horizontal-date-picker and upon select a date I'm calling a function in which I'm changing the state.
<HorizontalDatePicker
pickerType={'date'}
dayFormat={'Do'}
monthFormat={'MMM'}
yearFormat={'YYYY'}
returnDateFormat={'DD-MM-YYYY'}
onDateSelected={(date) => {
if (date) {
getTimeData()
}
}}
/>
Then in my getTimeData function I'm updating the const [timeSlots, setTimeSlots] = useState([]); state:
function getTimeData() {
...
if (timeAvailable) {
setTimeSlots(finalTimeSlots)
} else if (!timeAvailable) {
setTimeSlots([])
}
...
}
based on the timeSlots array I'm updating the UI, now I have to tap twice on the date to be able to see the results getting rendered.
I'm passing timeSlots to another custom component that I made:
<TimePicker timeSlotsArray={timeSlots} />
How do I achieve this in this scenario?
Related
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]);
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 just started learning about Mobx to implement it in my projects, and I've come across a big issue: I seem to not understand how actions work.
I've been following this nice tutorial: https://hackernoon.com/how-to-build-your-first-app-with-mobx-and-react-aea54fbb3265 (the complete code of the tutorial is located here: https://codesandbox.io/s/2z2r43k9vj?from-embed ), and it works smoothly. I've tried to do a small React App on my side, trying to do the same the tutorial mentioned, and yet it is failing. I am sure there is some small detail (since the app is pretty simple) that I am not seeing, so I would appreciate some help on it.
I've also tried to look for similar cases to mine, but I didn't find anything through a quick search (which makes me think even more the problem is insignificant...)
My code is this:
import React, { Component } from 'react';
import { decorate, observable, action, configure } from 'mobx';
import { observer } from 'mobx-react';
configure({ enforceActions: 'always' });
class Store {
my_number = 1;
addNumber() {
this.my_number += 1;
}
removeNumber() {
this.my_number -= 1;
}
}
decorate(Store, {
my_number: observable,
addNumber: action,
removeNumber: action
})
const my_store = new Store();
const Button = (props) => {
if (props.store.my_number === 1) {
return (
<div>
<button onClick={props.store.addNumber}>+</button>
</div>
)
} else if (props.store.my_number === 4) {
return (
<div>
<button onClick={props.store.removeNumber}>-</button>
</div>
)
} else {
return (
<div>
<button onClick={props.store.addNumber}>+</button>
<button onClick={props.store.removeNumber}>-</button>
</div>
)
}
}
const ObserverButton = observer(Button);
const DisplayNumber = (props) => {
return (
<h1>My number is: {props.store.my_number}</h1>
)
}
const ObserverDisplayNumber = observer(DisplayNumber);
export class SimpleMobxStore extends Component {
render() {
return (
<div>
<ObserverButton store={my_store} />
<ObserverDisplayNumber store={my_store} />
</div>
)
}
}
And my thoughts for developing it have been (I would also appreciate suggestions on how to improve my thoughts-flow if it's bad):
I want a text on the screen that shows a number between 1 and 4. Above this text I want to have a button that allows me to increase or decrease this number by adding or substracting a unit each time. I want this variable (the current number) to be stored in a separate store. That store will include:
My number
A method for increasing the number
A method for decreasing the number
In addition I will create two components: a button component that renders my button depending on the current number, and a display component.
My observable will be the number in the store, whereas the two methods will have to be decorated as actions, since they are changing the observed variable.
My button and display components will be observers, since they must be re-rendered once the number changes.
With this simple reasoning and code I was expecting it to function, but instead I'm getting a:
Error: [mobx] Since strict-mode is enabled, changing observed observable values outside actions is not allowed. Please wrap the code in an action if this change is intended. Tried to modify: Store#4.my_number
The log seems to be pointing to when I define const my_store = new Store();, but this is done in the tutorial and it works there.
Any idea on where this is failing and why?
Thank you
I think your action to the store is directly from render(). The tag to be precise. Try having a method outside the render and try changing the store state from there.
I have a FlatList in ReactNative which pulls a list of articles from an API. When the end of the list is reached on scrolling, a further page of articles is pulled from the API and appended to the articles list in a Redux reducer.
The FlatList is set up as:
render() {
return(
<FlatList data={this.props.articles.articles} // The initial articles list via Redux state
renderItem={this.renderArticleListItem} // Just renders the list item.
onEndReached={this.pageArticles.bind(this)} // Simply calls a Redux Action Creator/API
onEndReachedThreshold={0}
keyExtractor={item => item.id.toString()}/>
)};
The Redux 'articles' state object is mapped to the component using the React Redux connect function. The relevant reducer (some items removed for brevity) looks like:
/// Initial 'articles' state object
const INITIAL_STATE = {
articles: [],
loading: false,
error: '',
pageIndex: 0,
pageSize: 10
};
export default(state = INITIAL_STATE, action) => {
switch(action.type){
// The relevant part for returning articles from the API
case ARTICLES_SUCCESS:
return { ...state, loading: false, articles: state.articles.concat(action.payload.items),
pageIndex: action.payload.pageIndex, pageSize: action.payload.pageSize}
default:
return state;
}
}
The payload is a simple object - the articles are contained in the action.payload.items array, and there is additional paging information as well in the payload (not important to this problem).
Everything is fine with the API returning the correct data.
The problem is that when the end of the FlatList is reached on scrolling, the API is called, the new articles are pulled fine and appended to the this.props.articles state object and to the FlatList, BUT the FlatList jumps/scrolls back to the first item in the list.
I think the problem is probably with how I am returning the state in the Redux reducer but I'm not sure why.
Is using concat the correct way to return the new state with the new articles appended?
It might be too late to answer this but I experienced exact same problem having my data served from redux to the component and managed to fix the jumping effect by making my component a normal Component rather than PureComponent allowing me to use shouldComponentUpdate life-cycle hook method. This how the method should look like for you component:
shouldComponentUpdate(nextProps) {
if (this.props.articles === nextProps.articles) {
return false;
}
return true;
}
This method (if implemented) should return a boolean value indicating whether the component should update or not. What i did here was to prevent the component from re-rendering in case the contents of articles hasn't changed.
Hope this would be helpful for you or others who might have faced similar problem.
You need to add to listItem styles height and width. Freezing and jumping maybe because list tried to calculate sizes for all items even if they dont display.
And you can find answer in: https://github.com/facebook/react-native/issues/13727
Using FlatList as component and adding data as props re-renders whole content, so it scrolls to top. I recommend using it directly inside your page and changing its data using this.state, not props
I do have a ListView component with a renderRow() function. My custom ListBountiesView component which renders a ListView Row also takes a prop called cr and displays some content in each row depending on the value of cr.
The problem is that when this.props.customerRelationship changes its value, the ListView rows do not get updated.
I am doing it with: this.props.customerRelationship.points += responseJson.points;
I guess that ListView only updates when the data attribute changes, but how can I move props to my renderRow component so that they also update the ListView?
SuperScreen.js
renderRow(bounty) {
const { customerRelationship } = this.props;
return (
<ListBountiesView
key={bounty.id}
bounty={bounty}
cr={customerRelationship}
onPress={this.openDetailsScreen}
/>
);
}
render() {
const { bounties } = this.props;
return (
<ListView
data={bounties}
renderRow={this.renderRow}
loading={loading}
/>
)
The ListView refreshes the data source when the data prop gets a new reference:
componentWillReceiveProps(nextProps) {
if (nextProps.data !== this.props.data) {
this.setState({ dataSource: this.listDataSource.clone(nextProps.data) });
}
if (nextProps.loading !== this.props.loading) {
this.setLoading(nextProps.loading);
}
}
Similarly, React Native's ListView refreshes when its data source changes. This was discussed on their GitHub and in many other threads. The generally accepted workaround is to create a new data array. In your case, do it in componentWillReceiveProps whenever customerRelationship changes.
Move your customerRelationship to bounty object. Each bounty should have this property, then check it's value changed in the rowHasChanged. Other way is to check customerRelationship in componentWillReceiveProps function, if it's value changed clone bounties so all of it's child have new object reference.