I am trying to create a flatlist with list items. I managed to build one using one of the samples from https://facebook.github.io/react-native/docs/flatlist.html.
I am trying to extend this by creating something more complicated but I am stuck. I am trying to create a flatlist with list items like below. Ofcourse I can achive this by using one of those react native libraries but I am trying to avoid using libraries instead I want to construct a flatlist component with multiple renders because this approach would give me more control of the component. Would appreciate any help with this.
The easiest way to achieve it is to have a Row component and based on props you determine how to render it. Example:
class Row extends React.PureComponent {
render(){
const { item } = this.props
if(item.break){
return <Text>Break</Text>
}
return (
<View><Text>Normal item goes here</Text></View>
)
}
}
Related
I use React Native and Expo to develop an application on mobile and tablet.
The objective is to be able to answer a questionnaire where several questions are divided into various categories. A question may have a category or not, so they don't really follow each other in the code.
I use a loop to display my categories, with its questions inside. Questions are components, categories too.
When I answer a question, sometimes I want to reload another question specifically (or several). After answering my question, I have a list of questions I want to reload.
I would like either to launch a function in the component, or to reload it entirely.
How do I reload the question component, which may be quite far from the one I acted on?
Thanks for your help !
I wanted to listen with UseEffect for the modification of my global variable, but it doesn't work. Also, I can't fully reload my page either. I would like to specifically reload the question component or run the function.
What I have already tried:
Reloading the page entirely from my screen with a function in global, didn't work (
I have a lot of elements so I would like to avoid reloading everything)
Listen with useEffect the change of my list of questions to modify to check if my id was in it, but the listening is not done
I can't send functions or other elements in the props of my question because they can be in different components (category or other) so too far away.
Question Component (simplified) :
export default function RealisationQuestionComponent(props){
//When action in Question A
function changeCheckA(value) {
[...]
if (props.question.questions_impactees !== undefined) {
global.questions_impactees = props.question.questions_impactees;
}
}
//Effect in Question B
useEffect(() => {
[my function or reload entire component]
}, [global.questions_impactees]);
return (
<>...</>
)
EDIT :
Following the answer, I tried to use useContext to retrieve my information, but it tells me Can't find variable : RealContext
What i would like to do :
https://www.w3schools.com/react/showreact.asp?filename=demo2_react_context2
What I have done :
My screen AuditRealisationScreen
const RealContext = createContext();
const [listIdVictimes, setListIdVictimes] = useState('please test');
[...]
return (
<RealContext.Provider value={listIdVictimes}>
<RealisationChapitreComponent/>
</RealContext.Provider>
)
RealisationChapitreComponent > [...] > RealisationQuestionComponent
In my component RealisationQuestionComponent
const listTest = useContext(RealContext);
[...]
return (
<Text> {listTest} </Text>
)
Can it work this way?
Use [contexts][1]. Using [reducers][2] with context would be more flexible and organised.
If you have a lot of states to manage with mess of siblings and parent-child and child-parent relations then using [Redux][3] would give you more control to manage those components and its states
What I used do for
How to reload a component or call a function after action in another
component with React Native
const context = ... // declare
and then
// import context
const App=()=>{
...
return(
<Context.Provider value={your functions, data, states, props whatever you want}>
{{ ...child components }}
<Context.Provider/>
)
}
You can play with these contexts usage to achieve your goal
[1]: https://reactjs.org/docs/hooks-reference.html#usecontext
[2]: https://reactjs.org/docs/hooks-reference.html#usereducer
[3]: https://redux.js.org/introduction/why-rtk-is-redux-today#what-is-redux
I have requirement where I have to create the TextInputs, Buttons, and other UI components, but the issue is I have to create the UI directly from the JSON data provided like
{
key: "TextInput",
props: {
// some props of the component
}
}
I tried to find many libraries which can do such thing in React Native but not getting the results I want.
You import the JSON data and check if a value exists or map/loop through an array of values
So for instance
import data from 'data.json'
{data.key && (
<TextInput value={data.key}></TextInput>
)}
I'm new to React-Native, currently working a project that displays photos and its related information. The project uses the standard SectionList(RN 0.55).
The problem I have is that each time I add a photo, all the subcomponent in the list will be re-rendered. And I've noticed a significant slow down when the list grows to 50 something.
I have the following setup:
I have a redux store which contains Data(basically a wrapper around photo information), each time user does some action, the Data will be copied, modified, then reassigned back to redux store.
Then I have a class like following to render SectionList
class PhotoList extends PureComponent {
render() {
<SectionList
sections={deriveData(this.props.data)}
extraData={this.state}
renderItem={this.onRenderItem}
>
}
onRenderItem(item) {
return <View>
// two nested level components to hold information
</View>
}
driveData(data) {
// do a lot of data transformation and calculate derived value
return derivedData;
}
}
// data is redux connected
My primary confusing point is that, when SectionList takes in section in my case, the data(as a whole) is already a new copy and is modified(since a new photo is added), so it causes SectionList to re-renders everything?
I want SectionList to only additionally render the photo I just added, any suggestions?
Can you change the data ("data transformation and calculate derived value") at action and update that on redux 'data'. Then change like the following.
class PhotoList extends PureComponent {
render() {
<SectionList
sections={this.props.data} // Directly call data
extraData={this.props.data}
renderItem={this.onRenderItem}
>
}
onRenderItem(item) {
return <View>
// two nested level components to hold information
</View>
}
}
If you use redux then you have to handle data updating on redux. Then only the result will get.
Hi I am looking for the solution to change text dynamically.
I am writing code to show processing results on screen.
After some googling, I found there is a code to update text dynamically as follows.
But I would like to update text without any internal event. I want to change text from outside of the class. But I don't know how to implement it as I am a javascript and react-native beginner. There are other classes to process some functions so that I need to show the updated results using Results class which is an another component of the screen.
How can I deliver 'result' to Results class and how to update it dynamically and automatically?
class Results extends Component {
constructor() {
super()
this.state = {
log: 'Processing results'
}
}
updateText = (result) => {
this.setState({log: result})
}
render() {
return (
<View>
<Text onPress = {this.updateText}>
{this.state.log}
</Text>
</View>
)
}
}
This sounds to me that props can solve your problem.
Basically when you try to render Results class, pass along the value as a prop like below:
<Results dynamicText='HI' />
Then, from your Results class, access this external value via this.props.dynamicText as below
class Results extends Component {
render() {
return (
<View>
<Text>
{this.props.dynamicText}
</Text>
</View>
)
}
}
In addition to what #Issac answered, you can also hook up your current class to Redux and dispatch actions from another class to force state changes.
React Native and ReactJS has a different concept of how classes react to each other. Most other languages use inheritance based interactions to affect changes in classes other than itself. React itself is more composition based where changing the value/state/variable of one class requires either a state change or a prop change. The caveat to that us using Redux, which utilizes an overarching Store where any component that's connected to it can pull values or dispatch actions to change values.
I am new to react-native and am trying to build a Map component that relies on a GPS component. (I am actually not even sure if 'component' is the correct word)
I want to render the map using a UI, but I also need the GPS to get the location information.
Now, how can I create a GPS class including all the GPS logic, calling only a single function to update the location on the page page? Or more specifically, how can I separate the GPS code into a new file without having to call a <GPSComponent /> within the render method of the map-component?
To be more specific with the code example, I put it on CodePen here https://codepen.io/yeni/pen/WOrjJx
Just put your GPS class in a separate file. The class should not extend Component.
Then import your GPS class in your UI Component (e.g. import gps from './gps') and use it :)
another possible way is to return null inside render method
export default class GPSComponent extends React.Component{
constructor(props){
super(props);
// Do some stuff
}
someFunctions() { ... }
render(){
return null;
}
}