I Have 2 components, component a and component b
I want to navigate from component a to component b after changing a state.
When i change state, it triggers my componentWillReceiveProps function and i am navigation from there.
componentWillReceiveProps(nextProps) {
const { navigate } = nextProps.navigation;
navigate('b');
}
Now i got in an infinite loop, it starts triggering componentWillReceiveProps again and again instead of navigating
Help needed.
If you don't need compare current this.props and nextProps, you better trigger navigate action in somewhere else.
This link might also help you: https://facebook.github.io/react/docs/react-component.html#the-component-lifecycle
Related
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().
In my react-native project, I have three checkboxes, I need to track the state of those checkboxes so I use an object with key-value (value is boolean) to represent the states of all three checkboxes and use useState hook to manage them. Here is my code:
import React, { useState, useEffect } from 'react';
...
const MyScreen = ({ navigation }) => {
// initially, all checkboxes are checked
const initialCheckBoxState = {
0: true,
1: true,
2: true,
};
const [checkBoxesState, setCheckBoxesState] = useState(initialCheckBoxState);
useEffect(() => {
return () => {
console.log('Screen did unmount');
};
}, [checkBoxesState]);
return (
<View>
...
<SectionList
sections={options}
renderItem={({ index, item }) => (
<CheckBox
onPress={() => {
const checkBoxesStateCopy = { ...checkBoxesState };
checkBoxesStateCopy[index] = !checkBoxesStateCopy[index];
setCheckBoxesState(checkBoxesStateCopy);
}}
/>
)}
/>
...
</View>
);
};
I omitted code that is not the concern of my problem. As you can see, for each item I draw one CheckBox component.
In practice, there are always three items (i.e. three check boxes to show). At the beginning I declared initialCheckBoxState, each key-pair represents the state of the checkbox of each. In the onPress callback of Checkbox I toggle each check box state & update the checkBoxesState by hook method setCheckBoxesState as a whole.
Everything works fine at runtime, my screen is re-rendered when toggling checkbox state, UI shows the status of checkboxes correctly. But issue comes when I navigate back to the previous screen and navigate back to this screen, all checkboxes states are back to the initial states.
So, why the checkboxes states are not reserved?
P.S. previous screen and MyScreen are under the same stack navigator. User press a button of previous screen to navigate to MyScreen. From MyScreen user can go to previous screen by pressing the "headerLeft" button
First lets answer the question:
why the checkboxes states are not reserved?
This component is handling its state completely independent, the state is created & handled inside and no values are passed-in from outside. what does it mean? this component has its initial state value inside of itself, it doesn't use any prop or anything else to initialize the state. everytime this component gets created, state is again initialized with that value. so that's the reason you lose all changes done to checkboxes, because when you leave this screen(component) , it gets unmounted(we'll talk about this in next question) and because all values are just handled inside, every data (containing checkboxes state) will be lost.
So now lets talk about this:
is react-native supposed to reserve the state when come back to the screen?
short answer is No. Every component is destroyed when unmounted including their state and data.
Now lets answer why
screens are still on the stack in memory, not destroyed?
Usually developers use a package like react-navigation or RNRF(which is built on top of react-navigation) for react navigation, most of times we don't care about how they handle this navigation logic, we just use the interface the provided us. each of these packages may have their own way to handle navigation. providing full answer to determine why exactly the screen in still in memory needs full code review and sure lots of debugging but i guess there are 2 possibilities. first as i said maybe the package you are using keeps the unmounted screens in memory at least for a while for some reason. the 2nd is a common react community issue which is Unmounted component still in memory which you can check at: https://github.com/facebook/react/issues/16138
And at last lets answer the question:
how do i keep checkboxes state even with navigating back and losing component containing their state?
This doesn't have just one way to that but simple and short answer is move your state out of the that component, e.g move it out to the parent component or a global variable.
to make it more clear lets explain like this: imagine screen A is always mounted, then you go in B and there you can see some checkboxes and you can modify the states. if the state is handled completely inside B, if you navigate back from screen B to A you lose all changes because B is now unmounted. so what you should do it to put checkboxes states in A screen then pass the values down to B. and when modifying the values, you modify A state. so when B gets unmounted all changes are persistant because you have them in A.
other approached exists as well, you can create a global singleton object named globalState. then put values needed to share between multiple screens there. if you prefer redux or mobx you can use them. one of their usages is when you have some data that you need to share between mutiple screens, these data are independent from where you are at and will persist.
This explanation is from official react-navigation documentation:
Consider a stack navigator with screens A and B. After navigating to
A, its componentDidMount is called. When pushing B, its
componentDidMount is also called, but A remains mounted on the stack
and its componentWillUnmount is therefore not called.
When going back from B to A, componentWillUnmount of B is called, but
componentDidMount of A is not because A remained mounted the whole
time.
https://reactnavigation.org/docs/navigation-lifecycle/#example-scenario
Your MyScreen screen is equivalent to screen B from the example, which means you can expect your screen to stay mounted if you navigate forward, but not backwards.
Its simple, just add a keyExtractor to your SectionList component, which would uniquely identify each checkbox, so that react knows which one to re-render on update.
You'll want to use AsyncStorage to persist data to the device. State variables will be cleared any time the component unmounts.
AsyncStorage docs:
https://react-native-community.github.io/asaync-storage/
import AsyncStorage from '#react-native-community/async-storage';
//You can only store string values so convert objects to strings:
const storeData = async (value) => {
try {
const jsonValue = JSON.stringify(value)
await AsyncStorage.setItem('#storage_Key', jsonValue)
} catch (e) {
// saving error
}
}
const getData = async () => {
try {
const jsonValue = await AsyncStorage.getItem('#storage_Key')
return jsonValue != null ? JSON.parse(jsonValue) : null;
} catch(e) {
// error reading value
}
}
UPDATE -
State is not being persisted due to the nature of React Component lifecycles. Specifically, when you navigate away from a screen the lifecycle method componentWillUnmount is called.
Here's an excerpt from the docs:
componentWillUnmount() is invoked immediately before a component is unmounted and destroyed. Perform any necessary cleanup in this method, such as invalidating timers, canceling network requests, or cleaning up any subscriptions that were created in componentDidMount().
...Once a component instance is unmounted, it will never be mounted again.
This means any values stored in state will be destroyed as well and upon navigating back to the screen ComponentDidMount will be called which is where you may want to assign persisted values back to state.
Two possible approaches aside from AsyncStorage that may work for some use cases to persist data across screens is using Context or a singleton.
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.
There is some way to rerender a component after closing the drawer navigation (from
React-Navigation library)? Like an event or something like that?
Let me explain my problem: I'm not using a drawer navigation only for navigation purposes but also for settings in my app. For that reason, I want to change, for exemple, the language in my app and rerender the component behind the drawer (check the image). How can I achieve this?
Hope you can help me, thank you!
1) - Connect drawer to redux
2) - Dispatch and event when a setting is changed.
3) - Connect the component that needs re-rendering to redux settings state.
If the state is changed the component will automatically be re-rendered.
If you are not using redux you could try MobX or other alternatives:
https://medium.com/#machnicki/why-redux-is-not-so-easy-some-alternatives-24816d5ad22d
Without a proper state management what you want to achieve would probably add many ugly workarounds in the code.
I have done what you want to do with Redux, and I think that it is a good idea to use it.
Having said that, here is some code to know when the drawer is closed:
const defaultGetStateForAction = DrawerStack.router.getStateForAction;
DrawerStack.router.getStateForAction = (action, state) => {
switch (action.type) {
case "Navigation/DRAWER_CLOSED":
// Drawer is closing code goes here...
break;
}
return defaultGetStateForAction(action, state);
};
I am passing props and a function to the second page of the navigator as follows:
unlock: function(object) {
switch(true) {
case (object==0): this.setState({a: false});break;
case (object==1): this.setState({b: false});break;
case (object==2): this.setState({c: false});break;
case (object==3): this.setState({d: false});break;
default: this.setState({e: false});break;}
},
Then pass props through the navigator:
this.props.navigator.push({
title: title,
component: component,
passProps: {unlock: this.unlock,a: this.state.a, b: this.state.b,c: this.state.c,d: this.state.d, e: this.state.e}
});
But when I call the function in the second navigator page it updates ok but only to the home page. The information within this second navigator page does not update while I remain on the page. So for example this code:
<Text>{this.props.a}</Text?
Still shows the value prior to activating the function while in the second page. I have to go back to the main page and then return once more to the second page to see the updated value. This only seems to happen with the navigator. With any other method it updates instantly.
The only workaround I had was to both set state within the second page as well as setting props for the home page. It seems a bit of an unnecessary workaround though.
Have you call the unlock function in next component? Until you call it, it will not set the state of that main component, since unlock function is in main component it will only be called on main component , i think that your problem.