I have a class component directions in my project. I navigate to another component from it using this.props.navigation.navigate(). Now the problem is that I want to navigate back to the same directions component but with passing new values, ie I want it to reload from scratch, defining state variables once again. How can I do it?
Using navigation.navigate() simply takes me back to the previous state the screen has been.
this.props.navigation.navigate('direction',{
riderLocation:this.state.rideInfo.location,
ride_id:this.state.ride_id,
});
And this is the componentDidMount of directions.
componentDidMount(){
alert('componentDidMount');
const {navigation,route}=this.props;
this.state.riderLocation = navigation.getParam('riderLocation');
this.state.ride_id= navigation.getParam('ride_id');
}
In the "directions" component, use "componentDidMount" method.
Inside "componentDidMount" method, call a function which updates the state value as desired.
Once you are redirected back to the "directions" component, then "componentDidMount" will run and the state will be updated.
====
Edit:
Try using componentDidUpdate() method in "directions" component.
componentDidUpdate(prevProps, prevState) {
if (prevProps.navigation.getParam('ride_id') !== this.props.navigation.getParam('ride_id')) {
const {
navigation,
route
} = this.props;
this.setState({
riderLocation: navigation.getParam('riderLocation'),
ride_id: navigation.getParam('ride_id')
})
}
}
Also instead of "this.state.riderLocation" and "this.state.ride_id" use this.setState in componentDidMount(), just like I have written in componentDidUpdate().
Related
The context is a simple React Native app with React Navigation.
There are 3 screens.
The first simply displays a button to go to second screen using navigation.navigate("SecondScreen").
The Second contains a hook (see code below) that adds a listener to listen the mouse position. This hook adds the listener in a useEffect hook and removes the listener in the useEffect cleanup function. I just added a console.log in the listener function to see when the function is triggered.
This screen contains also a button to navigate to the Third screen, that only shows a text.
If I go from first screen to second screen: listener in hook start running. Good.
If I go back to the first screen using default react navigation 's back button in header. the listener stops. Good.
If I go again to second screen, then listener runs again. Good.
But if I now go from second screen to third screen, the listener is still running. Not Good.
How can I unmount the hook when going to third screen, and mount it again when going back to second screen?
Please read the following before answering :
I know that:
this is due to the fact that react navigation kills second screen when we go back to first screen, and then trigger the cleanup function returned by the useEffect in the hook. And that it doesn't kill second screen when we navigate to third screen, and then doesn't trigger the cleanup function.
the react navigation's hook useFocusEffect could be used to resolve this kind of problem. But it can't be used here because it will involve to replace the useEffect in the hook by the useFocusEffect. And I want my hook to be usable in every context, even if react navigation is not installed. More, I'm using here a custom hook for explanation, but it's the same problem for any hook (for example, the native useWindowDimensions).
Then does anyone know how I could manage this case to avoid to have the listener running on third screen ?
This is the code of the hook sample, that I take from https://github.com/rehooks/window-mouse-position/blob/master/index.js, but any hook could be used.
"use strict";
let { useState, useEffect } = require("react");
function useWindowMousePosition() {
let [WindowMousePosition, setWindowMousePosition] = useState({
x: null,
y: null
});
function handleMouseMove(e) {
console.log("handleMouseMove");
setWindowMousePosition({
x: e.pageX,
y: e.pageY
});
}
useEffect(() => {
window.addEventListener("mousemove", handleMouseMove);
return () => {
window.removeEventListener("mousemove", handleMouseMove);
};
}, []);
return WindowMousePosition;
}
module.exports = useWindowMousePosition;
the react navigation's hook useFocusEffect could be used to resolve this kind of problem. But it can't be used here because it will involve to replace the useEffect in the hook by the useFocusEffect. And I want my hook to be usable in every context, even if react navigation is not installed
So your hook somehow needs to know about the navigation state. If you can't use useFocusEffect, you'll need to pass the information about whether the screen is focused or not (e.g. with an enabled prop).
function useWindowMousePosition({ enabled = true } = {}) {
let [WindowMousePosition, setWindowMousePosition] = useState({
x: null,
y: null
});
useEffect(() => {
if (!enabled) {
return;
}
function handleMouseMove(e) {
console.log("handleMouseMove");
setWindowMousePosition({
x: e.pageX,
y: e.pageY
});
}
window.addEventListener("mousemove", handleMouseMove);
return () => {
window.removeEventListener("mousemove", handleMouseMove);
};
}, [enabled]);
return WindowMousePosition;
}
And then pass enabled based on screen focus:
const isFocused = useIsFocused();
const windowMousePosition = useWindowMousePosition({ enabled: isFocused });
Note that this approach will need the screen to re-render when it's blurred/focused unlike useFocusEffect.
I have an async function and a useEffect that fetches data once.
const [data, setData] = useState([]);
async function fetchData() {
fetch(`${baseURL}api/v1/data/${userId}`)
.then((response) => response.json())
.then((response) => {
try {
if (response.length > 0) {
setData(response);
} else {
setData([]);
// console.log(response);
}
} catch (err) {
console.log('no response');
alert(err);
}
});
}
useEffect(() => {
fetchData();
}, [userId, data]);
I could remove the array on the use effect but it will always run the function if I do that.
So when I open the screen, it will fetch the latest data. However, if I want to add a new data from a different screen, it wont trigger the async nor the useEffect function. How should I tell RN that there is a new data? Would AsyncStorage work? to update a data from one screen and apply the data here? I am open for suggestions on how to proceed.
What I meant by a different screen: A register screen and a view screen. In this case, I already opened the View Screen before I open the register screen so view screen is already rendered.
In React Navigation and most of the navigation libraries, screens don't get unmounted from the stack when it's navigated to another screen. For example if you have a list of something and then you press to "+" button to navigate to the "new item" screen to add a new one, when you press back button, since the previous "list" screen was not unmounted from the stack, useEffect won't be triggered, and you won't get the new data.
There are a couple of solutions for this case:
You can hold your data in a global state, and when you update an item from another screen, after a successful API call, you can also update the global state. You can look for React Context, MobX or Redux for this.
You can pass parent's state with a callback from one screen to another if they are not that apart from each other. So that in the "new data" screen, you can call that callback function to change the parent screen's state too.
Third, and IMO the best way is using a hook called useFocusEffect by React Navigation itself: https://reactnavigation.org/docs/use-focus-effect
I hope these will help.
I'm developing a react-native / redux app with a bottom-tab-navigator similar to the example at https://reactnavigation.org/docs/en/tab-based-navigation.html#customizing-the-appearance. My screens all connect to a Redux store and display shared data, however I'd like at least one of these screens to ignore the current data in the store and instead re-initialize this data each time it's navigated to (instead of continuing to display the data in whatever state it was last left in).
The screen has a method to do this, but I can't figure out how to call it after the first time the screen is rendered (e.g. from the constructor or componentDidMount() method). I can't call it from the render() method as this causes a "Cannot update during an existing state transition" error.
I need my navigator to somehow cause my HomeScreen.initializeData() method to be invoked each time the Home icon is pressed, but how do I do this?
HomeScreen.js:
initializeData() {
this.props.resetData(initialValue);
}
const initialValue = ...
(resetData() is a dispatch function that re-initializes the Redux store).
Updating state from render() would create an infinite loop. Also, you don’t want to run your state update every time the component re-render, only when the tab button is pressed. This tells me that the proper place to make your state update is some onPress function on the tab button.
So the question now relies on how to implement some onPress function on a tab button. I believe this answer this question:
Is there an onPress for TabNavigator tab in react-navigation?
So I found an answer, it's a little more complicated than might be expected: As Vinicius has pointed out I need to use the tabBarOnPress navigation option, but I also need to make my dispatch function available to this navigation option.
To do this I found I need to pass a reference to my dispatch function (which is available as a property of my screen) into the navigation option, so I've used navigation params to do this and here's what I've ended up with:
HomeScreen.js:
componentDidMount() {
initializeData(this.props);
this.props.navigation.setParams({ homeProps: this.props });
}
export const initializeData = (homeProps) => {
homeProps.resetData(initialValue);
};
const initialValue = ...
AppNavigator.js:
tabBarOnPress: ({navigation, defaultHandler}) => {
const routeName = navigation.state.routeName;
if (navigation.state.params === undefined) {
// no params available
} else if (routeName === 'Home') {
let homeProps = navigation.getParam('homeProps', null);
initializeData(homeProps);
} else if (routeName === ...
...
}
defaultHandler();
}
Notes:
I'm passing props as a navigation param rather than my dispatch function (which also works) as it's more flexible (e.g. it makes all of my dispatch functions available).
initializeData() is called both during construction of HomeScreen (for the first time the screen is displayed) and from the navigation icon (for subsequent displays of the screen).
It's necessary to check that params is defined within the navigation option as it'll be undefined the first time the screen is displayed (as screen construction has yet to occur). This also makes it necessary to call initializeData() during screen construction.
I have two screens: A and B, connected with a StackNavigator
Screen A is a QR code scanner. As soon as a QR code is scanned, it navigates to screen B.
In screen B, I make an API call using the QR code that gets passed as a navigation param from screen A. I trigger this API call in componentDidMount.
My issue is: if I navigate from A to B, then back to A, then to B again, componentDidMount does not get called and I have no way to trigger the API call.
EDIT:
Here's some code
Screen A
Handler function that gets called when a QR code is scanned:
handleQRCode = qrCode => {
NavigationService.navigate('Decode', {qrCode});
};
Screen B
The QR code is pulled from the navigation state params and used for an API call (startDecode) through redux.
componentDidMount() {
qrCode = this.props.navigation.state.params.qrCode;
this.props.startDecode(qrCode.data);
}
My issue is that componentDidMount only gets called the first time that route is taken.
In react-navigation each screen is kept mounted. This means that when you you go back to B, you might have changed the props, but componentDidMount was already invoked in the first creation of this screen.
There are two options available for you (AFAIK) that can handle this case:
Instead of calling this.props.navigation.navigate() you can use
this.props.navigation.push which will create another instance of
screen B, thus invoking the componentDidMount React lifecycle
event.
In screen B you can catch the event where its props have changed.
This can take place in the new static lifecycle event
getDerivedPropsFromState or it can be done in the soon to be
deprecated componentWillReceiveProps.
I was facing a similar issue and I used this.props.navigation.addListener() to resolve it. Basically, force-calling componentDidMount() may be possible by pushing same screen again using a key (I haven't tried it) but your stack will keep growing as well, which is not optimal. So, when you return to a screen already in stack, you can use addListener() to see if it is being re-focused, and you can replicate you componentDidMount() code here:
class MyClass extends Component {
someProcess = () => {
// Code common between componentDidMount() and willFocus()
}
componentDidMount() {
this.someProcess();
}
willFocus = this.props.navigation.addListener(
'willFocus',
(payload) => {
this.someProcess();
}
);
}
When MyClass is called for the first time, componentDidMount will get called. For the other times when it is still in stack but instead just gains focus, addListener will get called.
This happens because the B component is mounted only on the first time it is accessed, so componentDidMount won't be called again.
I recommend you to pass a callback to the setOnNavigatorEvent method of your navigator, with the 'didAppear' event. Your callback will be invoked on every event emitted by react-native-navigation, and you can verify to do your logic every time the screen appears (hence the use of 'didAppear' event). You can base your code on the following:
export default class ExampleScreen extends Component {
constructor(props) {
super(props);
this.props.navigator.setOnNavigatorEvent(this.onNavigatorEvent.bind(this));
}
onNavigatorEvent(event) {
if (event.id === 'didAppear') {
// do API call here
}
}
}
How can I pass new state to a React Navigation function?
My code currently looks like this:
Simplified view of my parent class:
constructor(props){
super(props)
this.state = {
code: "aaa"
}
this.refresh = this.refresh.bind(this)
}
refresh() {
this.setState({
code: "bbb"
})
}
async componentDidMount(){
const {navigate} = this.props.navigation
navigate("Child", {screen: "Screen Two", code: this.state.code, refresh: this.refresh})
}
In the child class I then do the following:
this.props.navigation.state.params.refresh()
The issue I am facing:
Option 1: If I have the code as it currently is, it will not pass the new state value to the navigator because it is not in the render function
Option 2: If I place the code in the render function, it gives me the warning: "Cannot update during an existing state transition".
What am I doing wrong and how can I fix this?
Further details
I am using this main screen to load some of the details from an API on the web and store them in state. I want to be able to pass a refresh function to the second screen that I will be able to use to reload data from the API onto the main screen. Once the data is loaded back into the state on the main screen it should propagate back down to the second screen. This seems easy to do without using a navigator, but I am not sure how to do it with a navigator.
I am not currently wanting to use redux due to the learning curve, but would like to look into it some time in the future.
So you are trying to call refresh() method inside your child component. If you use this inside render function the refresh() method will be called repeatedly and it will give a warning: "Cannot update during an existing state transition".
If you keep the code as it is, it will update the parent class state. But that update will not be reflected when you accessing this.props.navigation.state.params.code. This will only give the value 'aaa'.
Option 1;
You can use redux and easily handle this scenario.
Option 2;
If you really want to know the value of the parent class state you can pass a function as navigation params to child which will return the value of the state.
Parent class.
constructor(props){
super(props)
this.state = {
code: "aaa"
}
this.refresh = this.refresh.bind(this);
this.getState = this.getState.bind(this)
}
refresh() {
this.setState({ code: "bbb" })
}
getState() {
return this.state.code;
}
async componentDidMount(){
const {navigate} = this.props.navigation
navigate("Child", {screen: "Screen Two", code: this.state.code, refresh: this.refresh, getState: this.getState })
}
Inside your child class use the following code to get the parent class state.
let parentClassState = this.props.navigation.state.params.getState();