I am learning how to use React Hooks and have been stuck for many hours on something that's supposed to be very simple.
I am trying to display a a text if the state variable "loading" is true. If it's false, I want to display something else.
No matter what I try, "loading" is always false or at least, the UI does not appear to reflect its value.
here is the code:
import React, {useState, useEffect} from 'react';
import {View, SafeAreaView, Text} from 'react-native';
const testScreen= (props) => {
const [loading, setLoading ] = useState(true);
useEffect(() => {
setLoading(false);
}, []);
if(loading)
{
return <Text>Hi</Text>;
}
else
{
return<Text.Hey</Text>
}
}
export default testScreen;
Any help will be more than welcome and I am sorry if this is very basic.
UPDATE: Here is the actual code I am working with. SetLoading is supposed to update the state variable to false but never does or at least, the UI des not render.
import React, {useState, useEffect} from 'react';
import {View, SafeAreaView, Text, ActivityIndicator} from 'react-native';
import CategoryTag from '../Components/CategoryTag';
import firestore from '#react-native-firebase/firestore';
const CategoryScreen = (props) => {
const topicCollection = firestore().collection('Topics')
.where("active","==",true);
//hooks for topics
const [topics,setTopics] = useState([]);
const [loading, setLoading ] = useState(true);
//get all active topics
useEffect(() => {
return topicCollection.onSnapshot(querySnapshot => {
const list = [];
querySnapshot.forEach(doc => {
const { active, name } = doc.data();
list.push({
id: doc.id,
active,
name,
});
});
setTopics(list);
setLoading(false);
});
}, []);
const renderTopics = () =>{
return(
topics.map((item) =>{
return(
<CategoryTag key = {item.id}
color={userTopics.includes(item.name) ?"#51c0cc":"#303239"}
name = {item.name}
isSelected = {userTopics.includes(item.name)}
handleClick = {addTopicToUserTopicCollection}
/>
)
})
)
}
if(loading)
{
return (
<SafeAreaView style={{flex:1, backgroundColor:"#455a65"}}>
<View style={{width:200, padding:20, paddingTop:60}}>
<Text style ={{fontSize:25, fontWeight:"bold",
color:"#fff"}}>What are you</Text>
<Text style ={{fontSize:22, color:"#fff"}}>interested in?
</Text>
</View>
<View style={{flex:1, alignItems:"center",
justifyContent:"center", alignSelf:"center"}}>
<ActivityIndicator />
</View>
</SafeAreaView>
)
}
else // this never runs
{
return (
<SafeAreaView style={{flex:1, backgroundColor:"#455a65"}}>
<View>
<View style={{width:200, padding:20, paddingTop:60}}>
<Text style ={{fontSize:25, fontWeight:"bold",
color:"#fff"}}>What are you</Text>
<Text style ={{fontSize:22, color:"#fff"}}>interested in?
</Text>
</View>
<View style ={{flexDirection:"column", paddingTop:20}}>
<View style ={{padding:15, paddingTop:15,
marginBottom:15,
flexWrap:"wrap", flexDirection:"row"}}>
{renderTopics(topics)}
</View>
</View>
</View>
</SafeAreaView>
);
}
}
export default CategoryScreen;
You are immediately setting your setLoading state to false and therefore loading text might be rendering for fraction of second, or not at all, like a glitch. Try setting setLoading with a timeout and then you will see the intended behaviour.
const TestScreen= (props) => {
const [loading, setLoading ] = useState(true);
useEffect(() => {
setTimeout(()=>setLoading(false), 3000);
}, []);
if(loading)
{
return <Text>Hi</Text>;
}
else
{
return<Text>hey</Text>
}
}
Related
I'm trying to use Async Storage for a note app, I created a component called task.js as a template for todos, an navigation.js component for nav, and home.js for the main screen all display with <navigation /> inapp.js, I added a funcction to store object value using async storage, but is not working, everytime I hard reload the app everything will be gone but it is not giving me any errors, I don't know where to start
here is my Home.js
import React, {useState} from 'react';
import { Keyboard, KeyboardAvoidingView, Platform, StyleSheet, Text,
TextInput, TouchableOpacity, View, SafeAreaView, ScrollView, Image } from 'react-native';
import Task from '../components/Task';
import AsyncStorage from '#react-native-async-storage/async-storage';
export default function Home({ navigation }) {
const [task, setTask] = useState();
const [taskItems, setTaskItems] = useState([]);
React.useEffect ( () => {
save(taskItems);
}, [taskItems])
React.useEffect (() => {
getsave();
}, [])
const handleAddTask = () => {
Keyboard.dismiss();
setTaskItems([...taskItems, task])
setTask(null);
}
const completeTask = (index) => {
let itemsCopy = [...taskItems];
itemsCopy.splice (index, 1);
setTaskItems(itemsCopy)
}
const save = async taskItems =>{
try {
const savetask = JSON.stringify(taskItems)
await AsyncStorage.setItem('tasksave', savetask)
} catch (e) {
console.log(e);
}
};
const getsave = async () => {
try {
const taskItems = await AsyncStorage.getItem('tasksave');
if (taskItems != null){
setTaskItems(JSON.parse(taskItems));
}
} catch (error) {
console.log(e);
}
};
return (
<SafeAreaView style={styles.container}>
<View style={styles.tasksWrapper}>
<Text style={styles.sectionTitle}>Your stuff:</Text>
<TouchableOpacity onPress={() => navigation.navigate('About')}>
<Text style={styles.about}>About</Text>
</TouchableOpacity>
<ScrollView style={styles.items}>{
taskItems.map((item, index) => {
return (
<View key={index}>
<TouchableOpacity onPress={ () => navigation.navigate("Gas", {item})}>
<Task text={item} navigation={navigation} />
</TouchableOpacity>
<TouchableOpacity onPress={() => completeTask(index)} style={styles.deleteW}>
<Image style={styles.delete} source={require('../components/remove.png')}></Image>
</TouchableOpacity>
</View>
)
})
}
</ScrollView>
</View>
<KeyboardAvoidingView
behavior={Platform.OS === "ios" ? "padding" : "height"}
style={styles.textwrapper}>
<TextInput style={styles.input} placeholder={'message'} value={task} onChangeText={text => setTask(text)}></TextInput>
<TouchableOpacity onPress={() => handleAddTask()}>
<View style={styles.addWrap}>
<Text style={styles.add}>+</Text>
</View>
</TouchableOpacity>
</KeyboardAvoidingView>
</SafeAreaView>
);
}
Here's my Task.js:
import React from "react";
import { View, Text, StyleSheet, Image, TouchableOpacity } from "react-native";
const Task = (props, {navigation}) => {
return (
<View style={styles.item}>
<View style={styles.itemleft}>
<Image style={styles.lightball} source={require('./arabic.png')}></Image>
<Text style={styles.itemtext}>{props.text}</Text>
</View>
<Image style={styles.arrow} source={require('./rightarrow.png')}></Image>
</View>
)
}
const styles = StyleSheet.create({
export default Task;
I hope is a quick read, I took out all the style stuff but this is still kinda long sorry, if you think it has something to do with my app.js or nav.js I can give you those too, I usually slove these bugs on my own but I just have no idea where to begin cause I'm not getting any error messages, thank you
This is where my home screen is:
import React, { useState } from "react";
import {
StyleSheet,
View,
Text,
Button,
FlatList,
TouchableOpacity,
} from "react-native";
import { globalStyles } from "../styles/global";
import Card from "../shared/card";
import FlatButton from "../shared/button";
import { TextInput } from "react-native-gesture-handler";
import { AntDesign } from "#expo/vector-icons";
import Weather from "./weather";
export default function Home({ navigation }) {
//add state here
const [reviews, setReviews] = useState([
{ title: "Let's Snowboard", rating: 4, body: "blue", key: 1 },
]);
const [city, setCity] = useState("");
return (
<View style={globalStyles.container}>
<View style={styles.searchBox}>
<TextInput
placeholder="search"
placeholderTextColor="lightcoral"
style={styles.searchText}
onChange={(text) => setCity(text)}
/>
<TouchableOpacity style={styles.buttonTouch} onPress={Weather}>
<AntDesign name="search1" size={28} color="lightcoral" />
</TouchableOpacity>
</View>
<FlatList
data={reviews}
renderItem={({ item }) => (
<TouchableOpacity
onPress={() => navigation.navigate("Weather", item)}
>
<Card>
<Text style={globalStyles.titleText}>{item.title}</Text>
</Card>
</TouchableOpacity>
)}
/>
<FlatButton text="Let's snowboard?" />
</View>
);
}
For my weather screen:
import React, { useState } from "react";
import { StyleSheet, Text, View, Image } from "react-native";
import { globalStyles } from "../styles/global";
const Weather = () => {
const [date, setData] = useState([]);
const [icon, setIcon] = useState("");
const [cityDisplay, setCityDisplay] = useState("");
const [desc, setDesc] = useState("");
const [main, setMain] = useState("");
const [humidity, setHumidity] = useState("");
const [pressure, setPressure] = useState("");
const [visibility, setVisibility] = useState("");
const [temp, setTemp] = useState("");
async function fetchWeather() {
try {
const response = await fetch(
"https://samples.openweathermap.org/data/2.5/weather?q=London,uk&appid=***"
);
const json = await response.json();
setData({ data: json });
setTemp({ temp: (json.main.temp - 273.15).toFixed(2) + " C" });
setCityDisplay({ cityDisplay: json.name });
setIcon({ icon: json.weather[0].icon });
setMain({ main: json.weather[0].main });
setHumidity({ humidity: json.main.humidity + " %" });
setPressure({ pressure: json.main.pressure + " hPa" });
setVisibility({
visibility: (json.visibility / 1000).toFixed(2) + " km",
});
} catch (err) {
console.warn("error");
}
}
return (
<View style={styles.weatherBox}>
<View style={styles.weatherHolder}>
<Image
source={{
uri: "http://openweathermap.org/img/wn/" + setIcon + "#2x.png",
}}
style={styles.weatherImage}
/>
<View>
<Text style={styles.temperature}>{temp}</Text>
<Text>{cityDisplay}</Text>
</View>
</View>
</View>
);
};
Essentially, my goal is to click the card text where it says :let's snowboard. Once clicked, it should redirect me to the weather screen where at the moment, it will show me the current temperature and the name of the city. I am not sure why it's not showing. Im assuming it has something to do with my weather screen.
I had tested out making another simple screen where it would show the values of my current state 'reviews'. I was able to click the card and redirect me to another screen where it shows the rating value and the body.
This is the first time I've dealt with apis. Any guidance would be much appreciated(:
I am fairly certain that you do not actually call the fetchWeather function. In the Weather component you define the function with async function fetchWeather() {...}. However, that is only a function definition. You need to actually call it like this: fetchWeather(); which I think you can do right below the definition like the example below.
async function fetchWeather() {
// code that you want to execute in the function
}
// Actual function call
fetchWeather();
EDIT (concerning state management):
I would definitely recommend reading most of the React Hooks documentation to get a full grasp, but I will still address how you handle state.
At this location in the docs it shows exactly what I believe your issue to be.
Whenever you try to set state you do this: setVariable({ variableName: newValue});, but that is how you are supposed to set state inside of a class. However, fetchWeather() is a function, and functions are supposed to update state like this: setVariable(newValue);
Explanation: I am creating a fitness app, my fitness app has a component called WorkoutTimer that connects to the workout screen, and that screen is accessed via the HomeScreen. Inside the WorkoutTimer, I have an exerciseCount useState() that counts every time the timer does a complete loop (onto the next exercise). I have a different screen called StatsScreen which is accessed via the HomeScreen tab that I plan to display (and save) the number of exercises completed.
What I've done: I have quite literally spent all day researching around this, but it seems a bit harder with unrelated screens. I saw I might have to use useContext() but it seemed super difficult. I am fairly new to react native so I am trying my best haha! I have attached the code for each screen I think is needed, and attached a screenshot of my homeScreen tab so you can get a feel of how my application works.
WorkoutTimer.js
import React, { useState, useEffect, useRef } from "react";
import {
StyleSheet,
Text,
View,
TouchableOpacity,
Button,
Animated,
Image,
SafeAreaView,
} from "react-native";
import { CountdownCircleTimer } from "react-native-countdown-circle-timer";
import { Colors } from "../colors/Colors";
export default function WorkoutTimer() {
const [count, setCount] = useState(1);
const [exerciseCount, setExerciseCount] = useState(0);
const [workoutCount, setWorkoutCount] = useState(0);
const exercise = new Array(21);
exercise[1] = require("../assets/FR1.png");
exercise[2] = require("../assets/FR2.png");
exercise[3] = require("../assets/FR3.png");
exercise[4] = require("../assets/FR4.png");
exercise[5] = require("../assets/FR5.png");
exercise[6] = require("../assets/FR6.png");
exercise[7] = require("../assets/FR7.png");
exercise[8] = require("../assets/FR8.png");
exercise[9] = require("../assets/S1.png");
exercise[10] = require("../assets/S2.png");
exercise[11] = require("../assets/S3.png");
exercise[12] = require("../assets/S4.png");
exercise[13] = require("../assets/S5.png");
exercise[14] = require("../assets/S6.png");
exercise[15] = require("../assets/S7.png");
exercise[16] = require("../assets/S8.png");
exercise[17] = require("../assets/S9.png");
exercise[18] = require("../assets/S10.png");
exercise[19] = require("../assets/S11.png");
exercise[20] = require("../assets/S12.png");
exercise[21] = require("../assets/S13.png");
return (
<View style={styles.container}>
<View style={styles.timerCont}>
<CountdownCircleTimer
isPlaying
duration={45}
size={240}
colors={"#7B4FFF"}
onComplete={() => {
setCount((prevState) => prevState + 1);
setExerciseCount((prevState) => prevState + 1);
if (count == 21) {
return [false, 0];
}
return [(true, 1000)]; // repeat animation for one second
}}
>
{({ remainingTime, animatedColor }) => (
<View>
<Image
source={exercise[count]}
style={{
width: 150,
height: 150,
}}
/>
<View style={styles.timeOutside}>
<Animated.Text
style={{
color: animatedColor,
fontSize: 18,
position: "absolute",
marginTop: 67,
marginLeft: 35,
}}
>
{remainingTime}
</Animated.Text>
<Text style={styles.value}>seconds</Text>
</View>
</View>
)}
</CountdownCircleTimer>
</View>
</View>
);
}
const styles = StyleSheet.create({})
WorkoutScreen.js
import React, { useState } from "react";
import { StyleSheet, Text, View } from "react-native";
import WorkoutTimer from "../components/WorkoutTimer";
export default function WorkoutScreen() {
return (
<View style={styles.container}>
<WorkoutTimer />
</View>
);
}
const styles = StyleSheet.create({
container: {
flex: 1,
backgroundColor: "#fff",
alignItems: "center",
justifyContent: "center",
},
});
HomeScreen.js
import React from "react";
import { StyleSheet, Text, View, SafeAreaView, Button } from "react-native";
import { TouchableOpacity } from "react-native-gesture-handler";
import { AntDesign } from "#expo/vector-icons";
import { Colors } from "../colors/Colors";
export default function HomeScreen({ navigation }) {
return (
<SafeAreaView style={styles.container}>
<Text style={styles.pageRef}>SUMMARY</Text>
<Text style={styles.heading}>STRETCH & ROLL</Text>
<View style={styles.content}>
<TouchableOpacity
style={styles.timerDefault}
onPress={() => navigation.navigate("WorkoutScreen")}
>
<Button title="START WORKOUT" color={Colors.primary} />
</TouchableOpacity>
<TouchableOpacity
style={styles.statContainer}
onPress={() => navigation.navigate("StatsScreen")}
>
<AntDesign name="barschart" size={18} color={Colors.primary} />
<Text style={{ color: Colors.primary }}>Statistics</Text>
<AntDesign name="book" size={18} color={Colors.primary} />
</TouchableOpacity>
</View>
</SafeAreaView>
);
}
const styles = StyleSheet.create({})
StatsScreen.js
import React from "react";
import { StyleSheet, Text, View } from "react-native";
import { exerciseCount, workoutCount } from "../components/WorkoutTimer";
export default function StatsScreen() {
return (
<View style={styles.container}>
<Text display={exerciseCount} style={styles.exerciseText}>
{exerciseCount}
</Text>
<Text display={workoutCount} style={styles.workoutText}>
{workoutCount}
</Text>
</View>
);
}
const styles = StyleSheet.create({});
Home Screen Image
As far as I can tell, you're almost there! You're trying to get your 2 state
variables from the WorkoutTimer like this:
import { exerciseCount, workoutCount } from "../components/WorkoutTimer";
Unfortunatly this won't work :( . These two variables change throughout your
App's life-time and that kinda makes them "special".
In React, these kinds of variables need to be declared in a parent component
and passed along to all children, which are interested in them.
So in your current Setup you have a parent child relationship like:
HomeScreen -> WorkoutScreen -> WorkoutTimer.
If you move the variables to HomeScreen (HomeScreen.js)
export default function HomeScreen({ navigation }) {
const [exerciseCount, setExerciseCount] = useState(0);
const [workoutCount, setWorkoutCount] = useState(0);
you can then pass them along to WorkoutScreen or StatsScreen with something
like:
navigation.navigate("WorkoutScreen", { exerciseCount })
navigation.navigate("StatsScreen", { exerciseCount })
You'll probably have to read up on react-navigation's documentation for .navigate I'm not sure I remember this correctly.
In order to read the variable you can then:
export default function WorkoutScreen({ navigation }) {
const exerciseCount = navigation.getParam(exerciseCount);
return (
<View style={styles.container}>
<WorkoutTimer exerciseCount={exerciseCount} />
</View>
);
}
and finally show it in the WorkoutTimer:
export default function WorkoutTimer({ exerciseCount }) {
Of course that's just part of the solution, since you'll also have to pass
along a way to update your variables (setExerciseCount and setWorkoutCount).
I encourage you to read through the links I posted and try to get this to work.
After you've accumulated a few of these stateful variables, you might also want to look at Redux, but this is a bit much for now.
Your app looks cool, keep at it!
I ended up solving this problem with useContext if anyone is curious, it was hard to solve initially. But once I got my head around it, it wasn't too difficult to understand.
I created another file called exerciseContext with this code:
import React, { useState, createContext } from "react";
const ExerciseContext = createContext([{}, () => {}]);
const ExerciseProvider = (props) => {
const [state, setState] = useState(0);
//{ exerciseCount: 0, workoutCount: 0 }
return (
<ExerciseContext.Provider value={[state, setState]}>
{props.children}
</ExerciseContext.Provider>
);
};
export { ExerciseContext, ExerciseProvider };
and in App.js I used ExerciseProvider which allowed me to pass the data over the screens.
if (fontsLoaded) {
return (
<ExerciseProvider>
<NavigationContainer>
<MyTabs />
</NavigationContainer>
</ExerciseProvider>
);
} else {
return (
<AppLoading startAsync={getFonts} onFinish={() => setFontsLoaded(true)} />
);
}
}
I could call it with:
import { ExerciseContext } from "../components/ExerciseContext";
and
const [exerciseCount, setExerciseCount] = useContext(ExerciseContext);
This meant I could change the state too! Boom, solved! If anyone needs an explanation, let me know!
I think you have to use Mobx or Redux for state management. That will be more productive for you instead built-in state.
I'm trying to display data from an api and cant get a hold of using the forEach method correctly to show all the data at the same time. The API is working correctly. Here's the code:
import React, {useEffect, useState} from 'react'
import { Text, View, ActivityIndicator, ScrollView } from 'react-native'
import axios from '../../utils/axios'
//import CurrencyPair from '../../CurrencyPair'
function HomeScreen() {
const [data, setData] = useState([])
const [isLoading, setIsloading] = useState(true)
useEffect(() => {
const fetchpairs = async() => {
const result = await axios.get('/v3/accounts/{AccountId}/pricing?instruments=EUR_USD%2CUSD_CAD')
console.log(result.data)
setData(result.data)
setIsloading(false)
}
fetchpairs()
}, [])
if(isLoading) {
return (
<ActivityIndicator size="large"/>
)
}
else
return (
<ScrollView>
{[data].map((data) => (
data.forEach(data =>{
<Text>{JSON.stringify(data.prices[0].instrument)}
{JSON.stringify(data.prices[0].closeoutAsk)}
{JSON.stringify(data.prices[0].closeoutBid)}
</Text>
})
))}
</ScrollView>
)
}
export default HomeScreen
Map is already taking care of forEach function
<ScrollView>
{[data].map((item,i) => {
return(<Text key={i}>{JSON.stringify(item.prices[0].instrument)}
{JSON.stringify(item.prices[0].closeoutAsk)}
{JSON.stringify(item.prices[0].closeoutBid)}
</Text>
)}
)}
</ScrollView>
How is styling done after mapping data into a function in react native. The data is displayed correctly but in a raw format. I'd like the data being mapped to be styled into rows with space between each item. I have tried using a flatlist and it throws an error of invariant violation: tried to get frame for out of the range index nan. Kindly help.
import React, {useEffect, useState} from 'react'
import { Text, View, ActivityIndicator, ScrollView, StyleSheet } from 'react-native'
import axios from '../../utils/axios'
//import CurrencyPair from '../../CurrencyPair'
function HomeScreen() {
const [data, setData] = useState([])
const [isLoading, setIsloading] = useState(true)
useEffect(() => {
const interval = setInterval(() => {
const fetchpairs = async() => {
const results = await axios.get('/v3/accounts/{AccountId}/pricing?instruments=AUD_CAD%2CAUD_CHF%2CAUD_JPY%2CAUD_NZD%2CAUD_USD%2CCAD_CHF%2CCAD_JPY%2CCHF_JPY%2CEUR_AUD%2CEUR_CAD%2CEUR_CHF%2CEUR_GBP%2CEUR_NOK%2CEUR_NZD%2CEUR_USD%2CGBP_AUD%2CGBP_CAD%2CGBP_CHF%2CGBP_USD%2CGBP_JPY%2CNZD_CAD%2CNZD_CHF%2CNZD_JPY%2CUSD_CAD%2CUSD_JPY%2CUSD_CHF%2CUSD_ZAR%2CUSD_MXN')
console.log(results.data)
setData(results.data)
setIsloading(false)
}
fetchpairs()
},1000)
}, []);
if(isLoading) {
return (
<ActivityIndicator size="large"/>
)
}
else
return (
<ScrollView
contentContainerStyle={styles.contentContainer}
>
{data.prices && data.prices.map((prices, index) => {
return (
<Text key={index} style={styles.maintext}>
{data.prices[index].instrument}
{data.prices[index].closeoutAsk}
{data.prices[index].closeoutBid}
</Text>
)
})
}
</ScrollView>
)
}
const styles = StyleSheet.create({
contentContainer:{
flex: 1,
marginTop: 20,
justifyContent: "space-around"
}
})
export default HomeScreen
Just use flex to style.
{data.prices && data.prices.map((prices, index) => {
return (
<View
key={index}
style={{
flexDirection: 'row'
//justifyContent:'space-between'
}}>
<Text style={styles.maintext}>{data.prices[index].instrument}</Text>
<Text style={(styles.maintext, { marginLeft: 4 })}>{data.prices[index].closeoutAsk}</Text>
<Text style={(styles.maintext, { marginLeft: 4 })}>{data.prices[index].closeoutBid}</Text>
</View>
)
})
}