Develop Reference

there is a way to fix "Warning: Each child in a list should have a unique "key"?

Is there a way to fix this warning?
Warning: Each child in a list should have a unique "key
I got this warning every time and don't understand how to fix it.
I try to fix it but i realize that something wrong in my way .
hope to understand whats wrong because its so annoying.
import React, { Component } from 'react';
import { View, Text, StyleSheet, ActivityIndicator, Platform, FlatList, Dimensions, Image } from 'react-native';
import { HeaderButtons, Item } from 'react-navigation-header-buttons'
import HeaderButton from '../components/HeaderButton';
import axios from 'axios';
const { width, height } = Dimensions.get('window');
export default class PlacesListScreen extends Component {
constructor(props) {
super(props);
this.state = { isLoading: true, data: [] };
}
componentDidMount() {
axios.get('https://rallycoding.herokuapp.com/api/music_albums')
.then(res => {
this.setState({
isLoading: false,
data: res.data,
})
console.log(res.data);
})
}
renderItem(item) {
const { title, artist } = item.item;
return (
<View style={styles.itemView}>
<View style={styles.imgContainer}>
{/* <Image style={styles.imageStyle}
source={{ uri: image }}
/> */}
</View>
<View style={styles.itemInfo}>
<Text style={styles.name}>
{title+ ' ' + artist}
</Text>
<Text style={styles.vertical} numberOfLines={1}>{title} |</Text>
</View>
</View>
);
}
render() {
if (this.state.isLoading) {
return (
<View style={{ flex: 1, padding: 20 }}>
<Text style={{ alignSelf: 'center', fontWeight: 'bold', fontSize: 20 }}>loading...</Text>
<ActivityIndicator />
</View>
)
}
return (
<View style={styles.container}>
<FlatList
data={this.state.data}
renderItem={this.renderItem.bind(this)}
keyExtractor={item => item.id}
/>
</View>
);
}
}
Hope that you understand my problem and how can I fix it.
the example code above shows my try to get some data from API, but it returns a warning every time about
each child in a list should have a unique "key".

console.log the key of each item. It may be possible u have the same id for some items?

How to force Flatlist to re-render after getting a single data?

I've faced an issue with flatlist when I get single data from the server and set these into state and passes into data props, I can't see any update in the render "I'm adding some Loading if I'd not received any data I show an let's say Indicator" so the indicator disappears and I see blank screen!!
FYI, When I enable Hot Reloading and just press Save in my IDE I can see the single Data in my Screen!
So how can I force it to appear the data!
Code
import React, { Component } from "react";
import firebase from "react-native-firebase";
import Icon from "react-native-vector-icons/Ionicons";
import _ from "lodash";
import {
View,
Text,
StyleSheet,
FlatList,
TouchableOpacity,
Image,
Dimensions
} from "react-native";
const { width } = Dimensions.get("screen");
class ListChats extends Component {
constructor(props) {
super(props);
this.state = {
users: [],
noChat: true
};
}
_getUsers = () => {
let currentUser = firebase.auth().currentUser.uid;
let ref = firebase.database().ref(`Messages/${currentUser}`);
let usersKeys = [];
ref.once("value").then(snapshot => {
snapshot.forEach(childsnap => {
usersKeys.push(childsnap.key);
});
let usernames = [];
usersKeys.forEach(key => {
firebase
.database()
.ref("users")
.child(key)
.once("value")
.then(usersShot => {
let username = usersShot.val().username;
usernames.push({ username: username, key: key });
});
});
this.setState({ users: usernames,noChat: false });
});
};
componentDidMount() {
this._getUsers();
}
render() {
if (this.state.noChat) {
console.log("IF", this.state.users);
return (
<View style={styles.container}>
<Image
style={{
width,
height: width * 0.7,
resizeMode: "contain"
}}
source={require("../../assets/empty.gif")}
/>
<Text style={{ alignSelf: "center" }}>No Chats Found</Text>
</View>
);
} else {
console.log("Else", this.state.users);
return (
<View style={styles.container}>
<FlatList
key={Math.random() * 1000}
extraData={this.state} // I'm already added
data={this.state.users}
contentContainerStyle={{ flexGrow: 1 }}
renderItem={({ item }) => {
return (
<TouchableOpacity
onPress={() =>
this.props.navigation.navigate("ChatDetails", {
Key: item.key,
userName: item.username
})
}
>
<View style={styles.parent}>
<Icon name="ios-contact" size={50} color="#4d8dd6" />
<View
style={{
flex: 1,
justifyContent: "flex-start",
alignItems: "flex-start",
marginHorizontal: 25
}}
>
<Text
style={{
color: "#000",
fontSize: 17
// marginHorizontal: 25
// alignSelf: "stretch"
}}
>
{item.username}
</Text>
{/* <Text
style={{
color: "#a1a1a1",
marginHorizontal: 35,
marginVertical: 5,
alignSelf: "stretch"
}}
numberOfLines={1}
lineBreakMode="tail"
>
{item.lastMssg.text}
</Text> */}
</View>
<Icon name="ios-chatboxes" size={25} color="#d6d6d6" />
</View>
</TouchableOpacity>
);
}}
keyExtractor={(item, index) => index.toString()}
/>
</View>
);
}
}
}
const styles = StyleSheet.create({
container: {
flex: 1,
justifyContent: "center"
},
parent: {
flexDirection: "row",
justifyContent: "space-between",
alignItems: "center",
paddingVertical: 25,
marginHorizontal: 15,
borderBottomWidth: 1,
borderBottomColor: "#eee"
}
});
export default ListChats;

You have used extra data props but the issue is flatlist does a shallow data comparison so when the length of users changes it won't affect the flatlist so replace it with this.state.users
extraData={this.state.users}
You can see in the documentation it says flatlist is implementation of PureCompoment and PureComponent does a shallow comparison thats the reason it is not re-rendering.
https://reactnative.dev/docs/flatlist#extradata

to force the flatlist re-render. just add a boolean lets say "forceUpdate" to your state and whenever an item is added to flatlist data toggle that boolean and pass that to the extra data of your FlatList instead of the state.

Flatlist does not render if have one object in data?

I have some issue with Flatlist, I have an array of objects I got them from DB,
and save them to state, now when I log the this.state.providers in render() method or in the callback func after setState I got the valid Object like this
[{username: "Test", key: "53HoDga6aYhHsV5pCi5sx6LGbx42"}]
but when I passed these object into data prop in <Flatlist data={this.state.providers} /> the flatlist not rendering!
but when I add the object in the data prop manual like this
<Flatlist data={[{username: "Test One", key: "53HoDga6aYhHsV5pCi5sx6LGbx42"}]}
the flatlist work very well,
But I'm sure the code is correct because I added them into other project and work very well!!
Edit
when I pass tow object into the array the flatlist work!!
so how to handle it if I got one object from DB!
Code
import React, { Component } from "react";
import firebase from "react-native-firebase";
import Icon from "react-native-vector-icons/Ionicons";
import {
View,
Text,
StyleSheet,
FlatList,
TouchableOpacity,
Dimensions
} from "react-native";
class ListChats extends Component {
constructor(props) {
super(props);
this.state = {
providers: []
};
}
_chatList = () => {
let currentUser = firebase.auth().currentUser.uid;
let ref = firebase.database().ref(`Messages/${currentUser}`);
let providersKeys = [];
ref.once("value").then(snapshot => {
snapshot.forEach(childsnap => {
console.log(childsnap.key);
providersKeys.push(childsnap.key);
});
let usernames = [];
providersKeys.forEach(key => {
firebase
.database()
.ref("users")
.child(key)
.once("value")
.then(providersShot => {
let username = providersShot.val().username;
usernames.push({ username: username, key: key });
});
});
this.setState({ providers: usernames }, () =>
console.log(this.state.providers)
);
});
};
componentDidMount() {
this._chatList();
}
_listEmptyComponent = () => {
return (
<View style={styles.container}>
<Text style={{ alignSelf: "center" }}>No Chats Found :O</Text>
</View>
);
};
render() {
console.log(this.state.providers); // I got [{username: "Test", key: "53HoDga6aYhHsV5pCi5sx6LGbx42"}]
return (
<View style={{ flex: 1 }}>
<FlatList
key={Math.random() * 1000}
data={this.state.providers}
contentContainerStyle={{ flexGrow: 1 }}
ListEmptyComponent={this._listEmptyComponent()}
keyExtractor={item => item.key.toString()}
renderItem={({ item }) => {
console.log("item", item);
return (
<TouchableOpacity
onPress={() =>
this.props.navigation.navigate("ChatDetails", {
Key: item.key,
providerName: item.username
})
}
>
<View style={styles.parent}>
<Icon name="ios-contact" size={50} color="#4d8dd6" />
<View
style={{
flex: 1,
justifyContent: "flex-start",
alignItems: "flex-start",
marginHorizontal: 25
}}
>
<Text
style={{
color: "#000",
fontSize: 17
}}
>
{item.username}
</Text>
</View>
<Icon name="ios-chatboxes" size={25} color="#d6d6d6" />
</View>
</TouchableOpacity>
);
}}
// keyExtractor={(item, index) => index.toString()}
/>
</View>
);
}
}
const styles = StyleSheet.create({
container: {
flex: 1
},
parent: {
flexDirection: "row",
justifyContent: "space-between",
alignItems: "center",
paddingVertical: 25,
marginHorizontal: 15,
borderBottomWidth: 1,
borderBottomColor: "#eee"
}
});
export default ListChats;

You should add extraData property to FlatList:
extraData={this.state}

In here your using usernames.push method to add the data objects to array, using this method will not indicate the state about a need of a re-render even if the state is updated with a new array.
For this usual coding pattern is using the spread operator
this.setState({ providers: [...usernames] })

Use "extraData" props of FlatList.

Read the value of Parent state and pass Boolean to Child Component React

I'm having trouble learning how to pass data between parent and child in React Native.
In my parent component I have a state property (audioPlaying) which is a Boolean value.
state = {
//The title informs the Button and TitleArea components
title: 'hello',
audioPlaying: false,
};
I'd like to change that value on the press of a button (onPress).
<Button
title={this.state.title}
onPress={this.playPauseHandler}
audioPlaying={this.state.audioPlaying}
/>
...by calling the playPauseHandler.
playPauseHandler = () => {
this.setState(prevState => ({
audioPlaying: !prevState.audioPlaying
}));
}
Then in my child (Button) Component I want to evaluate the audioPlaying state property. If it's true, I want to show one things and false I want to show something else.
<View style={styles.playBtnStyle}>
{this.props.audioPlaying === false ? (
<MaterialIcons
name='play-arrow'
size={50}
color="#87888C"
/>
) : (
<MaterialIcons
name='pause'
size={50}
color="#87888C"
/>
)}
}
</View>
However, when I run this I get undefined for the value of audioPlaying.
React Native Error Message
Here are the full files for both:
App.js
import React, { Component } from 'react';
import { View, StatusBar } from 'react-native';
import Carousel from './src/components/Carousel/Carousel';
import Button from './src/components/Button/Button';
import TitleArea from './src/components/TitleArea/TitleArea';
import MapArea from './src/components/MapArea/MapArea';
const styles = {
container: {
flex: 1,
justifyContent: 'space-between',
},
playArea: {
flex: 1,
},
};
export default class App extends Component {
state = {
//The title informs the Button and TitleArea components
title: 'hello',
audioPlaying: false,
};
playPauseHandler = () => {
this.setState(prevState => ({
audioPlaying: !prevState.audioPlaying
}));
}
render() {
return (
<View style={styles.container}>
<TitleArea title={this.state.title} />
<StatusBar hidden={false} />
<Carousel />
<MapArea />
<Button
title={this.state.title}
onPress={this.playPauseHandler}
audioPlaying={this.state.audioPlaying}
/>
</View>
);
}
}
Button.js
import React, { Component } from 'react';
import { Text, View, TouchableOpacity, Dimensions } from 'react-native';
import MaterialIcons from 'react-native-vector-icons/MaterialIcons';
const { width } = Dimensions.get('window');
const height = width * 0.2;
const styles = {
textStyle: {
color: '#87888C',
fontSize: 18,
fontWeight: '600',
backgroundColor: 'white',
alignSelf: 'center',
},
buttonContainer: {
height,
flexDirection: 'row',
backgroundColor: 'white',
alignItems: 'center',
},
playBtnStyle: {
marginLeft: 50,
backgroundColor: 'white',
},
childStyle: {
flex: 1,
},
};
const button = (props) => {
return (
<View style={styles.buttonContainer}>
<TouchableOpacity>
<View style={styles.playBtnStyle}>
{this.props.audioPlaying === false ? (
<MaterialIcons
name='play-arrow'
size={50}
color="#87888C"
/>
) : (
<MaterialIcons
name='pause'
size={50}
color="#87888C"
/>
)}
}
</View>
</TouchableOpacity>
<View style={styles.childStyle}>
<Text style={styles.textStyle}>Chapter 1: {props.title}</Text>
</View>
</View>
);
}
export default button;

There is no this in the context of button. That is just a function returning JSX.
Instead, use props
<View style={styles.playBtnStyle}>
{props.audioPlaying === false ? (
<MaterialIcons
name='play-arrow'
size={50}
color="#87888C"
/>
) : (
<MaterialIcons
name='pause'
size={50}
color="#87888C"
/>
)}
</View>

Ok so I solved my own problem! (step one to being a developer)
Two issues:
Capturing Touch Events
React Native has what's called Touchables. According to the documentation these are "wrappers that make views respond properly to touches".
TouchableOpacity, the one I'm using:
On press down, the opacity of the wrapped view is decreased, dimming it. Opacity is controlled by wrapping the children in an Animated.View, which is added to the view hierarchy.
https://facebook.github.io/react-native/docs/touchablewithoutfeedback#onpress
All Touchables accept the onPress prop. So by adding the onPress prop to the Touchable, I'm able to capture the touch event instead of just firing it.
Passing Callback to Parent
This article helped me understand more about how a parent function can be called from a child.
https://medium.com/#thejasonfile/callback-functions-in-react-e822ebede766
So I'm calling playPause() (I renamed the prop and destructured it) in TouchableOpacity, which fires from a touch event causing state to change and component to re-render.
const button = (props) => {
const {
title,
audioPlaying,
playPause,
} = props;
return (
<View style={styles.buttonContainer}>
<TouchableOpacity onPress={() => playPause()}>
<View style={styles.playBtnStyle}>
{audioPlaying === false ? (
<MaterialIcons
name='play-arrow'
size={50}
color="#87888C"
/>
) : (
<MaterialIcons
name='pause'
size={50}
color="#87888C"
/>
)
}
</View>
</TouchableOpacity>
<View style={styles.childStyle}>
<Text style={styles.textStyle}>
Chapter 1:
{title}
</Text>
</View>
</View>
);
};

Conditional Rendering of child elements in React

I am trying to write a reusable Header Component in React-Native. I want to write it in a ways that the left and right button can be passed as child components. To know where to render which button I want to pass a prop like rightIcon or leftIcon. However I don't know how to access these props.
This is my App.js file
import React from 'react';
import {StyleSheet, TouchableHighlight, View} from 'react-native';
import Header from "./src/Header";
import {Ionicons} from '#expo/vector-icons';
export default class App extends React.Component {
render() {
return (
<View style={styles.container}>
<Header headerText={"Barcode Scanner"}>
<TouchableHighlight righticon>
<Ionicons name="md-barcode" size={36} color="white"></Ionicons>
</TouchableHighlight>
</Header>
</View>
);
}
}
const styles = StyleSheet.create({
container: {
flex: 1
},
});
And this is the Header Component
import React from 'react';
import {Text, View} from 'react-native';
export default class Header extends React.Component {
render() {
const {textStyle, viewStyle, rightButton} = styles;
return (
<View style={viewStyle}>
<Text style={textStyle}>{this.props.headerText}</Text>
<View style={rightButton}>
{this.renderRightChild()}
</View>
</View>
);
}
renderRightChild = () => {
console.log("Check if rightIcon Prop is set");
}
}
const styles = {
viewStyle: {
backgroundColor: '#5161b8',
justifyContent: 'center',
alignItems: 'center',
height: 80,
paddingTop: 25,
shadowColor: '#000',
shadowOffset: {width: 0, height: 2},
shadowOpacity: 0.2,
elevation: 2,
position: 'relative'
},
textStyle: {
color: '#fff',
fontSize: 20
},
rightButton: {
position: 'absolute',
top:
35,
right:
20
}
}
;
I already tried to use React.Children.toArray but this always throws an error that the request entity is too large.
Thanks for all the answers

I guess you can always use a render prop that way you can not only decide whether to render left/right icon component but the component rendering the icon does not even have to know what to render:
The term “render prop” refers to a simple technique for sharing code
between React components using a prop whose value is a function.
return (
<View style={styles.container}>
<Header
headerText={"Barcode Scanner"}
renderRightIcon={() => (
<TouchableHighlight righticon>
<Ionicons name="md-barcode" size={36} color="white" />
</TouchableHighlight>
)}
/>
</View>
);
Then you can use call the right icon as a function:
return (
<View style={viewStyle}>
<Text style={textStyle}>{this.props.headerText}</Text>
{renderLeftIcon && (
<View style={leftButton}>
{renderLeftIcon()}
</View>)
}
{renderRightIcon && (
<View style={rightButton}>
{renderRightIcon()}
</View>)
}
</View>
);

You render both components, the right and left and you put an if condition inside state.
Header Component render method
render() {
const { leftOrRight } = this.props // right - true, left - false
return(
...
{ leftOrRight ? <RightIcon /> : <LeftIcon />}
);
}
Inside Component that calls Header
import Header from './somepath ...';
class Something extends React.Component {
this.state = { leftOrRight }
render() {
return(
<Header leftOrRight = {this.state.LeftOrRight}/>
);
}
}
You could have a function that sets leftOrRight in your parent class

One way to do this is write a Header Component and pass all the things, as props, which you can then access them in Header Components Props like..
<Header title="HeaderTitle"
leftButtonTitle="LeftButton"
rightButton={canBeAObjectWithSomeInfo}
leftButtonClick={handleClick} />
and then in your header component(can be class or a function)
const Header = ({}) => (
<View>
<View onPress={this.props.handleClick}>{this.props.leftButton}</View>
<View>{this.props.title}</View>
<View onPress={this.props.handleRightClick}>{this.props.rightButton}</View>
</View>
)
something like this you can have and then you can design header accordingly