Develop Reference

React.Native: Flat List not showing up

I am trying to return two things, a separate Mission component and a flat list. When I run my emulator, I can get the return on the Mission component but not the flat list. There are no errors, so I'm a bit lost with how to approach this issue. I even double-checked my imports. Here is the code:
import React, { Component } from "react";
import { ScrollView, Text, FlatList } from 'react-native';
import Mission from './Mission';
import PARTNERS from '../shared/partners';
import { ListItem } from 'react-native-elements';
class About extends Component {
constructor(props) {
super(props);
this.state = {
partners: PARTNERS,
}
};
static navigationOptions = {
title: 'About Us'
}
render() {
const { navigate } = this.props.navigation;
const renderPartner = ({ item }) => {
return (
<ListItem
title={item.name}
subtitle={item.description}
leftAvatar={{ source: require('./images/bootstrap-logo.png') }}
/>
);
};
return (
<ScrollView>
<Mission />
<FlatList
data={this.state.partners}
renderItem={renderPartner}
keyExtractor={item => item.id.toString()}
/>
</ScrollView >
);
}
}
export default About;

import React, { Component } from 'react';
import { FlatList, View, Text } from 'react-native';
import { ListItem, Card } from 'react-native-elements';
import { FILMS } from '../shared/films';
/*
When working correctly, when you hit "Tap to play" in the simulated mobile device to the right, you will see a list of films from shared/films.js.
Before updating this code:
- You must be logged into your Expo account (create an account if you do not have one already)
- Use the Save button on the upper right corner to fork this Snack to your account. Name it as you please, or accept the default random name.
Share the link to your version in the forum for this code challenge.
Your challenges: 1. Fix the component by adding a constructor and adding the data imported as FILMS to the component's state
2. In the FlatList, use that state data for films in the 'data' attribute.
3. In the ListItem, add the film title as the title, and the director as the subtitle.
4. Update films.js to add a third film of your choice.
Bonus Challenge: Write a custom view in the ListItem subtitle to show more details about each film, such as the release year, genre, language.
*/
class FilmCatalogue extends Component {
constructor(props) {
super(props);
this.state = {
films: FILMS
}
}
render() {
const renderFilm = ({item}) => {
return (
<ListItem
title={item.title}
titleStyle={{fontWeight: 700, color: 'dark-grey'}}
subtitle={
<View >
<Text style={{fontStyle: "italic", fontWeight: 500}}>{item.director}</Text>
<Text>{item.category}</Text>
<Text>{item.language}</Text>
</View>
}
rightSubtitle={item.year}
bottomDivider
/>
);
};
return (
<Card title="Film Catalogue">
<FlatList
data={this.state.films}
renderItem={renderFilm}
keyExtractor={item=>item.id.toString()}
/>
</Card>
);
}
}
export default FilmCatalogue;
i used this on an expo snack to display a list of the files i had in this file (the Film Catalogue Component.js)
hope this kind of helps!

An error occurred while displaying the result of the request in a text component. using the fetch () method

It is not an error in fact, but it is not showing the result of the request in the component.
First I made the request, and I want to show the response of my request in a Text component, but the empty component appears when rendering
import React, {Component} from 'react';
import {View, Button, Text} from 'react-native'
export default class App extends Component{
constructor(){
super();
url = 'https://b7web.com.br/todo/25088';
this.state = {
lista:''
}
carregaDados = () => {
fetch(this.url)
.then(
(res)=> res.json()
)
.then(
(res)=>this.setState({lista:res.todo})
);
}
}
render(){
return(
<View>
<Text>{this.state.lista}</Text>
</View>
);
}
}

The problem is that you are trying to render an array of objects inside a component and also you haven't gived the View a style, making render every children inside a single line.
If you want to render an element you have to cycle trough the array trough a .map() or use a Flatlist.
An example would be:
<View style={{flex:1}}>
{this.state.lista!==''&&this.state.lista.map((item, index) =>
<Text key={index}>{item.item}</Text>
}
</View>

Calling onPress on custom component in React Native

How to solve this? I have a custom Button component that gets included in my ModalScreen. It all seems to work but the onPress function is acting up. It seems to have lost the scope for some reason so I can't reference this or even add params to the function. What am I missing here?
import React from 'react';
import {
Text,
View,
} from 'react-native';
import Styles from 'app/constants/Styles';
import Button from 'app/components/Button';
export default class ModalScreen extends React.Component {
onBtnPress() {
console.log('dfsdfsdf'); /// << this gets consoled out just fine
//this.props.navigation.navigate('Main'); <<<< this won't work
}
render() {
return (
<View style={Styles.center}>
<Text>MOdalScreen</Text>
<Button label='Gå vidare' onPress={ this.onBtnPress }/>
</View>
);
}
}
Button.js
import React, { Component } from 'react';
import { View, Text, TouchableOpacity } from 'react-native';
import Styles from 'app/constants/Styles'
import Vars from 'app/constants/Vars'
export default class Button extends Component {
render() {
return (
<TouchableOpacity style={[Styles.round, Styles.primaryBackground]} onPress={this.props.onPress}>
<Text style={[Styles.label, Styles.textCenter, { margin: Vars.spacing.narrow }]}>
{this.props.label}
</Text>
</TouchableOpacity>
)
}
}

You're right that it's lost the scope. You just need to bind the scope to the handle function somehow before you give it to the Button component. One popular way is with a handy arrow function:
<Button label='Gå vidare' onPress={ () => this.onBtnPress() }/>
Or you could use bind in the constuctor:
export default class ModalScreen extends React.Component {
constructor(props) {
super(props);
this.onBtnPress = this.onBtnPress.bind(this)
}
onBtnPress() {
console.log('dfsdfsdf'); /// << this gets consoled out just fine
//this.props.navigation.navigate('Main'); <<<< this won't work
}

infinite Render in React

I am having problem figuring out why my application is doing endless render.
Inside, My stateful component, I am calling a redux action in componentDidMount method (calling componentWillMount also do endless render)
class cryptoTicker extends PureComponent {
componentDidMount() {
this.props.fetchCoin()
// This fetches some 1600 crypto coins data,Redux action link for the same in end
}
render() {
return (
<ScrollView>
<Header />
<View>
<FlatList
data={this.state.searchCoin ? this.displaySearchCrypto : this.props.cryptoLoaded}
style={{ flex: 1 }}
extraData={[this.displaySearchCrypto, this.props.cryptoLoaded]}
keyExtractor={item => item.short}
initialNumToRender={50}
windowSize={21}
removeClippedSubviews={true}
renderItem={({ item, index }) => (
<CoinCard
key={item["short"]}
/>
)}
/>
</View>
</ScrollView>
)
}
}
In CoinCard I am literally doing nothing besides this (Notice CoinCard inside Flat list)
class CoinCard extends Component {
render () {
console.log("Inside rende here")
return (
<View> <Text> Text </Text> </View>
)
}
}
Now, When I console log in my coincard render, I can see infinite log of Inside rende here
[Question:] Can anyone please help me figure out why this could be happening?
You can click here to see my actions and click here to see my reducer.
[Update:] My repository is here if you want to clone and see it by yourself.
[Update: 2]: I have pushed the above shared code on github and it will still log endless console.log statements (if you can clone, run and move back to this commit ).
[Update:3]: I am no longer using <ScrollView /> in <FlatList /> also when I mean endless render, I mean is that it is endless (& Unecessarily) passing same props to child component (<Coincard />), if I use PureComponent, it won't log endlessly in render () { but in componentWillRecieveProps, If I do console.log(nextProps), I can see the same log passed over and over again

There are some points to note in your code.
The CoinCard Component must be a PureComponent, which will not re-render if the props are shallow-equal.
You should not render your Flatlist inside the ScrollView component, which would make the component render all components inside it at once which may cause more looping between the Flatlist and ScrollView.
You can also a definite height to the rendered component to reduce the number of times component is rendered for other props.
Another thing to note is, only props in the component are rendered on scroll bottom, based on the log statement mentioned below.
import {Dimensions} from 'react-native'
const {width, height} = Dimensions.get('window)
class CoinCard extends React.PureComponent {
render () {
console.log(this.props.item.long) //... Check the prop changes here, pass the item prop in parent Flatlist. This logs component prop changes which will show that same items are not being re-rendered but new items are being called.
return (
<View style={{height / 10, width}}> //... Render 10 items on the screen
<Text>
Text
</Text>
</View>
)
}
}
UPDATE
This extra logging is due to the props being from the Flatlist to your component without PureComponent shallow comparison.
Note that componentWillReceiveProps() is deprecated and you should avoid them in your code.
React.PureComponent works under the hood and uses shouldComponentUpdate to use shallow comparison between the current and updated props. Therefore log console.log(this.props.item.long) in your PureComponent' render will log the unique list which can be checked.

Like izb mentions, the root cause of the pb is the business call that is done on a pure component whereas it is just loaded. It is because your component make a business decision (<=>"I decide when something must be showed in myself"). It is not a good practice in React, even less when you use redux. The component must be as stupid a possible and not even decide what to do and when to do it.
As I see in your project, you don't deal correctly with component and container concept. You should not have any logic in your container, as it should simply be a wrapper of a stupid pure component. Like this:
import { connect, Dispatch } from "react-redux";
import { push, RouterAction, RouterState } from "react-router-redux";
import ApplicationBarComponent from "../components/ApplicationBar";
export function mapStateToProps({ routing }: { routing: RouterState }) {
return routing;
}
export function mapDispatchToProps(dispatch: Dispatch<RouterAction>) {
return {
navigate: (payload: string) => dispatch(push(payload)),
};
}
const tmp = connect(mapStateToProps, mapDispatchToProps);
export default tmp(ApplicationBarComponent);
and the matching component:
import AppBar from '#material-ui/core/AppBar';
import IconButton from '#material-ui/core/IconButton';
import Menu from '#material-ui/core/Menu';
import MenuItem from '#material-ui/core/MenuItem';
import { StyleRules, Theme, withStyles, WithStyles } from '#material-ui/core/styles';
import Tab from '#material-ui/core/Tab';
import Tabs from '#material-ui/core/Tabs';
import Toolbar from '#material-ui/core/Toolbar';
import Typography from '#material-ui/core/Typography';
import AccountCircle from '#material-ui/icons/AccountCircle';
import MenuIcon from '#material-ui/icons/Menu';
import autobind from "autobind-decorator";
import * as React from "react";
import { push, RouterState } from "react-router-redux";
const styles = (theme: Theme): StyleRules => ({
flex: {
flex: 1
},
menuButton: {
marginLeft: -12,
marginRight: 20,
},
root: {
backgroundColor: theme.palette.background.paper,
flexGrow: 1
},
});
export interface IProps extends RouterState, WithStyles {
navigate: typeof push;
}
#autobind
class ApplicationBar extends React.PureComponent<IProps, { anchorEl: HTMLInputElement | undefined }> {
constructor(props: any) {
super(props);
this.state = { anchorEl: undefined };
}
public render() {
const auth = true;
const { classes } = this.props;
const menuOpened = !!this.state.anchorEl;
return (
<div className={classes.root}>
<AppBar position="fixed" color="primary">
<Toolbar>
<IconButton className={classes.menuButton} color="inherit" aria-label="Menu">
<MenuIcon />
</IconButton>
<Typography variant="title" color="inherit" className={classes.flex}>
Title
</Typography>
<Tabs value={this.getPathName()} onChange={this.handleNavigate} >
{/* <Tabs value="/"> */}
<Tab label="Counter 1" value="/counter1" />
<Tab label="Counter 2" value="/counter2" />
<Tab label="Register" value="/register" />
<Tab label="Forecast" value="/forecast" />
</Tabs>
{auth && (
<div>
<IconButton
aria-owns={menuOpened ? 'menu-appbar' : undefined}
aria-haspopup="true"
onClick={this.handleMenu}
color="inherit"
>
<AccountCircle />
</IconButton>
<Menu
id="menu-appbar"
anchorEl={this.state.anchorEl}
anchorOrigin={{
horizontal: 'right',
vertical: 'top',
}}
transformOrigin={{
horizontal: 'right',
vertical: 'top',
}}
open={menuOpened}
onClose={this.handleClose}
>
<MenuItem onClick={this.handleClose}>Profile</MenuItem>
<MenuItem onClick={this.handleClose}>My account</MenuItem>
</Menu>
</div>
)}
</Toolbar>
</AppBar>
</div >
);
}
private getPathName(): string {
if (!this.props.location) {
return "/counter1";
}
return (this.props.location as { pathname: string }).pathname;
}
private handleNavigate(event: React.ChangeEvent<{}>, value: any) {
this.props.navigate(value as string);
}
private handleMenu(event: React.MouseEvent<HTMLInputElement>) {
this.setState({ anchorEl: event.currentTarget });
}
private handleClose() {
this.setState({ anchorEl: undefined });
}
}
export default withStyles(styles)(ApplicationBar);
Then you will tell me: "but where do I initiate the call that will fill my list?"
Well I see here that you use redux-thunk (I prefer redux observable... more complicated to learn but waaaaaaaaaaaaaaaaay more powerful), then this should be thunk that initiates the dispatch of this!
To summarize:
Components: the stupidest element that normally should have only the render method, and some other method handler to bubble up user events. This method only takes care of showing its properties to the user. Don't use the state unless you have a visual information that belongs only to this component (like the visibility of a popup for example). Anything that is showed or updated comes from above: a higher level component, or a container. It doesn't decide to update its own values. At best, it handles a user event on a subcomponent, then bubble up another event above, and... well maybe at some point, some new properties will be given back by its container!
Container: very stupid logic that consists in wrapping a top level component into redux for it to plug events to actions, and to plug some part of the store to properties
Redux thunk (or redux observable): it is the one that handles the whole user application logic. This guy is the only one who knows what to trigger and when. If a part of your front end must contain the complexity, it's this one!
Reducers: define how to organize the data in the store for it to be as easily usable as possible.
The store: ideally one per top level container, the only one that contains the data that must be showed to the user. Nobody else should.
If you follow these principles, you should never face any issue like "why the hell this is called twice? and... who made it? and why at this moment?"
Something else: if you use redux, use an immutability framework. Otherwise you may face issues as reducers must be pure functions. For this you can use a popular one immutable.js but not convenient at all. And the late ousider that is actually a killer: immer (made by the author or mobx).

It seems Jacob in the above comment has managed to make the component render only twice.
This will definitely cause double initial render (and would cause an infinite render if it wasn't a PureComponent):
componentDidUpdate() {
var updateCoinData;
if (!updateCoinData) { // <- this is always true
updateCoinData = [...this.props.cryptoLoaded];
this.setState({updateCoinData: true}); // <- this will trigger a re render since `this.state.updateCoinData` is not initially true
}
...
}
Link to the issue in your repository

Error: this.props.header is not a function when using StackNavigator

I have a screen inside my react-navigation StackNavigator that looks like this:
import React from 'react';
import { FlatList, ScrollView, StyleSheet, Text, View } from 'react-native';
import { List, ListItem } from 'react-native-elements';
import Accordion from '#ercpereda/react-native-accordion';
export default class PassportScreen extends React.Component {
static navigationOptions = {
title: 'Passport Recovery',
};
constructor(props) {
super(props);
this.renderItem = this.renderItem.bind(this);
}
renderItem(item) {
return (
<View>
<Accordion
header={item.item.key}
content={item.item.content}
/>
</View>
)
}
render() {
const instructions = [
{
key: <Text>1. Fill out a passport application form</Text>,
content: <Text>Content</Text>
},
{
key: <Text>2. Fill out a lost/missing passport statement</Text>,
content: <Text>Content</Text>
},
///...etc
];
return (
<ScrollView>
<FlatList
data={instructions}
renderItem={this.renderItem}
/>
</ScrollView>
)
}
}
module.exports = PassportScreen;
however, when I click to navigate to this screen from another screen, I get this error: TypeError: this.props.header is not a function. (In 'this.props.header({
isOpen: this.state.is_visible
})', 'this.props.header' is an instance of Object).
Other questions I've looked at with similar errors have mentioned passing props to the constructor and needing to pass this.renderItem instead of this.renderItem(), both of which I have already done, so I'm wondering if the problem comes from the fact that this screen is inside a StackNavigator and is navigated to by clicking on a ListItem. Is my intuition correct? If so, how can I fix this?

It seems that the header prop accepts a function, rather than just a component like content does.

Right now you're directly passing an object to the header prop, therefore it won't accept the callback function.
You may try the following approach in order to pass a callback to the header.
PassportScreen.js
customFunc = (callback) => {
console.log(callback)
}
renderItem = (item) => { // Useful to bind `this`
return (
<View>
<Accordion
header={this.customFunc}
content={item.item.content}
/>
</View>
)
}
ChildComponent.js
this.props.header('I'm setting the callback here')