I'm making an app using React Native and facing a problem while making a countdown timer.
I needed to use setInterval in order to implement this, but I found that setInterval will not act what I have expected.
So I used custom Hooks from this post, and here's the code:
import React, { useState, useEffect, useRef } from 'react';
function useInterval(callback, delay) {
const savedCallback = useRef();
// Remember the latest callback.
useEffect(() => {
savedCallback.current = callback;
}, [callback]);
// Set up the interval.
useEffect(() => {
function tick() {
savedCallback.current();
}
if (delay !== null) {
let id = setInterval(tick, delay);
return () => clearInterval(id);
}
}, [delay]);
}
After that, I made a button to make a timer to be triggered:
const [leftTime, setTime] = useState(300000);
const triggerTimer = () => {
useInterval(() => setTime(leftTime - 1), 1000);
};
return (
<>
<Text>{leftTime}</Text>
<TouchableOpacity onPress={() => triggerTimer()}
<Text>Start Countdown!</Text>
</TouchableOpacity>
</>
);
However, I got an error saying 'Invalid hook call. Hooks can only be called inside of the body of a function component.'
I already know that Hooks must be called at the very top of the function component, but is there any way to trigger a hook by pressing a button in the app?
Also, I want to stop the timer automatically and do something after that when the state 'leftTime' becomes 0.
Related
I want to run method when focus screen, i use this:
useEffect(() => {
const unsubscribe = navigation.addListener('focus', () => {
console.log(
'test'
);
});
return unsubscribe;
}, [navigation]);
but it doesnt work. it gives an error like this :
*
An effect function must not return anything besides a function, which
is used for clean-up. You returned: [object Object]
also even i dont return anything, console.log(
'test'
) doest work
I am using navigation V4
Is this working?
import { useFocusEffect } from '#react-navigation/native';
......
useFocusEffect(useCallback(() => {
......
console.log(something)
}, [something]));
//-------
If not check if react navigation is configured correctly.
UPDATE
In React navigation 4.x you will have to follow one of the methods in this guide https://reactnavigation.org/docs/4.x/function-after-focusing-screen/
For useEffect to work properly, the flow is following:
in the square brackets in the end you add a variable which triggers the action. In your case it only triggers on the firs run, and on navigation variable change
you should run your function within useEffect. You have only defined a constant in the body of useEffect, but you never run it.
optionally you may return a function in the end of a run. This function is triggered only when the component unmounts, and used to avoid memory leaks.
Based on this: I'm not sure what are you trying to achieve (unclear from your original post), but this may be what you want:
useEffect(() => {
navigation.addListener('focus', () => {
console.log(
'test'
);
});
const unsubscribe = () => navigation.removeListener('focus'); // !!! I'm not sure about this one, check the docs how to unsubscribe !!!
return unsubscribe;
}, [navigation]); // << triggers useEffect
Assuming you are using the latest version of react-navigation you must the use-focus-effect.
https://reactnavigation.org/docs/use-focus-effect/
Your code should be updated as mentioned below
useFocusEffect(
useCallback(() => {
const unsubscribe = () => {
console.log("test");
}
return () => unsubscribe();
}, [userId])
);
I want to navigate the user to another screen in react native project after native app widget click in android. I was able to catch event using native event emitter in my MainView.js and there i changed state of one of my component and it got changed but UI is not getting rendered after this state change. It is showing blank screen and there is not error on the console. Thanks in advance for any help!!
export default class MainView extends React.Component {
constructor(props) {
super(props);
this.state = {text: 'Hi, This is main screen for app widget!!!'};
}
componentDidMount() {
const eventEmitter = new NativeEventEmitter();
this.listener = eventEmitter.addListener('MyCustomEvent', (event) => {
console.log('MyCustomEvent -->', event);
console.log('MyCustomEvent ArticleId -->', event.ArticleId);
if (event.ArticleId === data.articleId) {
console.log('data ArticleId true', data.articleId);
//navigation.push('Article Details', data);
this.setState({
text: data.articleDes,
});
// setText(data.articleDes);
console.log('text -->', this.state.text);
} else {
// setText('No such article found.');
console.log('text -->', this.state.text);
}
});
}
componentWillUnmount() {
this.eventListener.remove(); //Removes the listener
}
render() {
return (
<View style={{flex: 1}}>
<Text>{this.state.text}</Text>
<Button
title="click"
onPress={() => this.props.navigation.push('Article Details', data)}
/>
</View>
);
}
}
CustomActivity source code which is launched from appwidget click. From this activity's oncreate, I'm emitting events to react-native main view.
int articleId = 0;
if (getIntent() != null) {
articleId = getIntent().getIntExtra("articleId", 0);
Log.e("articleid", "" + articleId);
}
// Put data to map
WritableMap payload = Arguments.createMap();
payload.putInt("ArticleId", articleId);
// Emitting event from java code
ReactContext context = getReactNativeHost().getReactInstanceManager().getCurrentReactContext();
if ( context != null && context.hasActiveCatalystInstance()) {
Log.e("react context", "not null");
(getReactNativeHost().getReactInstanceManager().getCurrentReactContext())
.getJSModule(DeviceEventManagerModule.RCTDeviceEventEmitter.class)
.emit("MyCustomEvent", payload);
}
That is not how to use NativeEventEmitter. You need to initialise the NativeEventEmitter with the native module you are emitting events from:
import { NativeEventEmitter, NativeModules } from 'react-native';
const { myNativeModule } = NativeModules;
componentDidMount() {
...
const eventEmitter = new NativeEventEmitter(myNativeModule);
this.eventListener = eventEmitter.addListener('myEvent', (event) => {
console.log(event.eventProperty) // "someValue"
});
...
}
componentWillUnmount() {
this.eventListener.remove(); //Removes the listener
}
Read more about NativeModules here: https://reactnative.dev/docs/native-modules-android
This sound familiar with an issue I am experiencing on IOS. The code is similar, but I cannot guarantee that the underlying structure in Android works in the same way. Anyways, I am sending an event message from IOS-Native (written in swift in xCode) to React-native file using the NativeEventEmitter. After the initial render, the value just wont update, and as I understand this issue is not limited to this type of Event. After some googling I found out that everything you read from state inside that event-callback has a reference to only the first render, and will not update on future renders.
Solution; use useRef so you keep a reference to the the updated value. useRef keeps the value across renders and event-callbacks. This is not something I have found out myself, please look at https://medium.com/geographit/accessing-react-state-in-event-listeners-with-usestate-and-useref-hooks-8cceee73c559 and React useState hook event handler using initial state for, they are the one that deserves the credit.
I'm trying to test the OnDidFocus event in my React Native app using react navigation 4 and using the following event listener:
useEffect(() => {
const willFocusSub = props.navigation.addListener(
"onDidFocus",
console.log("testing onDidFocus")
);
return () => {
willFocusSub.remove();
};
});
When I first load the page it works fine but when I move away and then come back to the same screen through the Back button it does not seem to perceive the focus event.
This is my stack
const MovieNavigator = createStackNavigator(
{
MoviesList: HomeMovies,
MovieDetail: MovieDetailScreen,
PopularMovies: PopularMoviesScreen,
CrewMember: CastDetailScreen,
GenreSearch: GenreSearchScreen,
MovieSearch: MovieSearchScreen,
},
I'm in MoviesList and the event is triggered fine, then I move to MovieDetail. If I hit Back and return to MoviesList the event onDidFocus is not triggered at all.
I think you could try "willFocus" instead.
Like this:
const willFocusSub = props.navigation.addListener(
"willFocus",
()=>{console.log("testing willFocus")}
);
Try modyfying your useEffect call to this!
useEffect(() => {
const willFocusSub = props.navigation.addListener(
"onDidFocus",
console.log("testing onDidFocus")
);
return () => {
willFocusSub.remove();
};
},[]);
I found another way to detect the focus and blur event and seems the only way to track an event when using the Back button.
Instead of subscribing to events, I'm check the focus status of the screen using the useIsFocused() hooks available from react-navigation-hooks library.
import { useIsFocused } from "react-navigation-hooks";
...
const [showGallery, setShowGallery] = useState(true);
...
useEffect(() => {
if (isFocused) {
setShowGallery(true);
} else {
setShowGallery(false);
}
console.log("isFocused: " + isFocused);
}, [isFocused]);
Basically I'm checking the status of the screen using isFocused hook every time it changes (when it leaves and returns only same as didFocus and didBlur) and setting the state setShowGallery accordingly to run the carousel when focused and stop it when blurred.
Hope it helps others!
As the docs https://reactnavigation.org/docs/en/next/use-focus-effect.html,
"Sometimes we want to run side-effects when a screen is focused. A side effect may involve things like adding an event listener, fetching data, updating document title, etc."
I'm trying to use useFocusEffect to fetch data everytime that the user go to that page.
on my component I have a function which dispatch an action with redux to fetch the data:
const fetchData = ()=>{
dispatch(companyJobsFetch(userDetails.companyId));
};
Actually I'm using useEffect hook to call fetchData(), but I'd like to fetch data everytime that the user go to that page and not only when rendered the first time.
It's not clear from the documentation how to use useFocusEffect and I'm not having success on how to do it.
Any help?
The docs show you how to do it. You need to replace API.subscribe with your own thing:
useFocusEffect(
React.useCallback(() => {
dispatch(companyJobsFetch(userDetails.companyId));
}, [dispatch, companyJobsFetch, userDetails.companyId])
);
For version react navigation 4.x, you can use addEvent listener
useEffect(() => {
if (navigation.isFocused()) {
resetReviews(); // replace with your function
}
}, [navigation.isFocused()]);
OR
useEffect(() => {
const focusListener = navigation.addListener('didFocus', () => {
// The screen is focused
// Call any action
_getBusiness({id: business?.id}); // replace with your function
});
return () => {
// clean up event listener
focusListener.remove();
};
}, []);
For later version 5.x, you can use hooks to achieve this
import { useIsFocused } from '#react-navigation/native';
// ...
function Profile() {
const isFocused = useIsFocused();
return <Text>{isFocused ? 'focused' : 'unfocused'}</Text>;
}
I'm trying to make a weather app that gets the user's location when they open the app. I was given starter code that uses a button that gets the user's location when it's pressed. How can do I change the code so that it fires the contents of the _onPress function when the app is opened?
My starter code:
import React, { Component } from "react";
import Button from "./../Button";
import styles from "./style.js";
const style = { backgroundColor: "#DDDDDD" };
class LocationButton extends Component {
_onPress() {
navigator.geolocation.getCurrentPosition(
initialPosition => {
this.props.onGetCoords(
initialPosition.coords.latitude,
initialPosition.coords.longitude
);
},
error => {
alert(error.message);
},
{ enableHighAccuracy: true, timeout: 20000, maximumAge: 1000 }
);
}
render() {
return (
<Button
label="Use Current Location"
style={style}
onPress={this._onPress.bind(this)}
/>
);
}
}
export default LocationButton;
I had read that componentWillMount() will fire before render, so I tried inserting the following code after the _onPress() function, but I got an error stating 'Can't find variable: _onPress'
componentWillMount() {
_onPress();
}
I'm sure the solution is simple - I'm very new to ReactNative. I will gladly give any additional information if need be. Thank you!
_onPress() doesn't exist because it's not bound to anything until the render method. Just_onPress() actually doesn't exist anywhere. To fix this, change_onPress() to an arrow function by changing the function declaration from _onPress(){} to _onPress = () => {}, then call it in componentDidMount via this._onPress(). You'll also have to change your onPress to onPress={this._onPress}. The second way of fixing this still requires you to change your onPress to onPress={this._onPress}, but also to create a constructor and bind your function there by doing this.onPress = this.onPress.bind(this).