Develop Reference

Child component rendering multiple times [duplicate]

I don't know why my React component is rendering twice. So I am pulling a phone number from params and saving it to state so I can search through Firestore. Everything seems to be working fine except it renders twice... The first one renders the phone number and zero points. The second time it renders all the data is displayed correctly. Can someone guide me to the solution.
class Update extends Component {
constructor(props) {
super(props);
const { match } = this.props;
this.state = {
phoneNumber: match.params.phoneNumber,
points: 0,
error: ''
}
}
getPoints = () => {
firebase.auth().onAuthStateChanged((user) => {
if(user) {
const docRef = database.collection('users').doc(user.uid).collection('customers').doc(this.state.phoneNumber);
docRef.get().then((doc) => {
if (doc.exists) {
const points = doc.data().points;
this.setState(() => ({ points }));
console.log(points);
} else {
// doc.data() will be undefined in this case
console.log("No such document!");
const error = 'This phone number is not registered yet...'
this.setState(() => ({ error }));
}
}).catch(function(error) {
console.log("Error getting document:", error);
});
} else {
history.push('/')
}
});
}
componentDidMount() {
if(this.state.phoneNumber) {
this.getPoints();
} else {
return null;
}
}
render() {
return (
<div>
<div>
<p>{this.state.phoneNumber} has {this.state.points} points...</p>
<p>Would you like to redeem or add points?</p>
</div>
<div>
<button>Redeem Points</button>
<button>Add Points</button>
</div>
</div>
);
}
}
export default Update;

You are running your app in strict mode. Go to index.js and comment strict mode tag. You will find a single render.
This happens is an intentional feature of the React.StrictMode. It only happens in development mode and should help to find accidental side effects in the render phase.
From the docs:
Strict mode can’t automatically detect side effects for you, but it can help you spot them by making them a little more deterministic. This is done by intentionally double-invoking the following functions:...
^ In this case the render function.
Official documentation of what might cause re-rendering when using React.StrictMode:
https://reactjs.org/docs/strict-mode.html#detecting-unexpected-side-effects

This is because of React Strict Mode code.
Remove -> React.StrictMode, from ReactDOM.render code.
Will render 2 times on every re-render:
ReactDOM.render(
<React.StrictMode>
<App />
</React.StrictMode>,
document.getElementById('root')
);
Will render 1 time:
ReactDOM.render(
<>
<App />
</>,
document.getElementById('root')
);

React is rendering the component before getPoints finishing the asynchronous operation.
So the first render shows the initial state for points which is 0, then componentDidMount is called and triggers the async operation.
When the async operation is done and the state been updated, another render is triggered with the new data.
If you want, you can show a loader or an indicator that the data is being fetched and is not ready yet to display with conditional rendering.
Just add another Boolean key like isFetching, set it to true when you call the server and set it to false when the data is received.
Your render can look something like this:
render() {
const { isFetching } = this.state;
return (
<div>
{isFetching ? (
<div>Loading...</div>
) : (
<div>
<p>
{this.state.phoneNumber} has {this.state.points} points...
</p>
<p>Would you like to redeem or add points?</p>
<div>
<button>Redeem Points</button>
<button>Add Points</button>
</div>
</div>
)}
</div>
);
}

React.StrictMode, makes it render twice, so that we do not put side effects in following locations
constructor
componentWillMount (or UNSAFE_componentWillMount)
componentWillReceiveProps (or UNSAFE_componentWillReceiveProps)
componentWillUpdate (or UNSAFE_componentWillUpdate)
getDerivedStateFromProps
shouldComponentUpdate
render
setState updater functions (the first argument)
All these methods are called more than once, so it is important to avoid having side-effects in them. If we ignore this principle it is likely to end up with inconsistent state issues and memory leaks.
React.StrictMode cannot spot side-effects at once, but it can help us find them by intentionally invoking twice some key functions.
These functions are:
Class component constructor, render, and shouldComponentUpdate methods
Class component static getDerivedStateFromProps method
Function component bodies
State updater functions (the first argument to setState)
Functions passed to useState, useMemo, or useReducer
This behaviour definitely has some performance impact, but we should not worry since it takes place only in development and not in production.
credit: https://mariosfakiolas.com/blog/my-react-components-render-twice-and-drive-me-crazy/

it is done intentionally by react to avoid this
remove
<React.StrictMode> </React.StrictMode>
from index.js

I worked around this by providing a custom hook. Put the hook below into your code, then:
// instead of this:
useEffect( ()=> {
console.log('my effect is running');
return () => console.log('my effect is destroying');
}, []);
// do this:
useEffectOnce( ()=> {
console.log('my effect is running');
return () => console.log('my effect is destroying');
});
Here is the code for the hook:
export const useEffectOnce = ( effect => {
const destroyFunc = useRef();
const calledOnce = useRef(false);
const renderAfterCalled = useRef(false);
if (calledOnce.current) {
renderAfterCalled.current = true;
}
useEffect( () => {
if (calledOnce.current) {
return;
}
calledOnce.current = true;
destroyFunc.current = effect();
return ()=> {
if (!renderAfterCalled.current) {
return;
}
if (destroyFunc.current) {
destroyFunc.current();
}
};
}, []);
};
See this blog for the explanation.

Well, I have created a workaround hook for this. Check this, if it helps:
import { useEffect } from "react";
const useDevEffect = (cb, deps) => {
let ran = false;
useEffect(() => {
if (ran) return;
cb();
return () => (ran = true);
}, deps);
};
const isDev = !process.env.NODE_ENV || process.env.NODE_ENV === "development";
export const useOnceEffect = isDev ? useDevEffect : useEffect;
CodeSandbox Demo: https://github.com/akulsr0/react-18-useeffect-twice-fix

React internally monitors & manages its render cycles using its virtual dom and its diffing algorithms, so you need not worry about the number of re-renders. Let the re-renders to be managed by react. Even though the render function is getting invoked, there are sub components which doesn't gets refreshed on ui, if there is no props or state change inside it. Every setstate function call will inform react to check the diffing algorithm, and invoke the render function.
So in your case, since you have a setstate defined inside the getPoints function, it tells react to rerun the diffing process through the render function.

React Warning: Cannot update a component from inside the function body of a different component

I am using Redux with Class Components in React. Having the below two states in Redux store.
{ spinner: false, refresh: false }
In Parent Components, I have a dispatch function to change this states.
class App extends React.Component {
reloadHandler = () => {
console.log("[App] reloadComponent");
this.props.onShowSpinner();
this.props.onRefresh();
};
render() {
return <Child reloadApp={this.reloadHandler} />;
}
}
In Child Component, I am trying to reload the parent component like below.
class Child extends React.Component {
static getDerivedStateFromProps(props, state) {
if (somecondition) {
// doing some redux store update
props.reloadApp();
}
}
render() {
return <button />;
}
}
I am getting error as below.
Warning: Cannot update a component from inside the function body of a
different component.
How to remove this warning? What I am doing wrong here?

For me I was dispatching to my redux store in a React Hook. I had to dispatch in a useEffect to properly sync with the React render cycle:
export const useOrderbookSubscription = marketId => {
const { data, error, loading } = useSubscription(ORDERBOOK_SUBSCRIPTION, {
variables: {
marketId,
},
})
const formattedData = useMemo(() => {
// DISPATCHING HERE CAUSED THE WARNING
}, [data])
// DISPATCHING HERE CAUSED THE WARNING TOO
// Note: Dispatching to the store has to be done in a useEffect so that React
// can sync the update with the render cycle otherwise it causes the message:
// `Warning: Cannot update a component from inside the function body of a different component.`
useEffect(() => {
orderbookStore.dispatch(setOrderbookData(formattedData))
}, [formattedData])
return { data: formattedData, error, loading }
}

If your code calls a function in a parent component upon a condition being met like this:
const ListOfUsersComponent = ({ handleNoUsersLoaded }) => {
const { data, loading, error } = useQuery(QUERY);
if (data && data.users.length === 0) {
return handleNoUsersLoaded();
}
return (
<div>
<p>Users are loaded.</p>
</div>
);
};
Try wrapping the condition in a useEffect:
const ListOfUsersComponent = ({ handleNoUsersLoaded }) => {
const { data, loading, error } = useQuery(QUERY);
useEffect(() => {
if (data && data.users.length === 0) {
return handleNoUsersLoaded();
}
}, [data, handleNoUsersLoaded]);
return (
<div>
<p>Users are loaded.</p>
</div>
);
};

It seems that you have latest build of React#16.13.x. You can find more details about it here. It is specified that you should not setState of another component from other component.
from the docs:
It is supported to call setState during render, but only for the same component. If you call setState during a render on a different component, you will now see a warning:
Warning: Cannot update a component from inside the function body of a different component.
This warning will help you find application bugs caused by unintentional state changes. In the rare case that you intentionally want to change the state of another component as a result of rendering, you can wrap the setState call into useEffect.
Coming to the actual question.
I think there is no need of getDerivedStateFromProps in the child component body. If you want to trigger the bound event. Then you can call it via the onClick of the Child component as i can see it is a <button/>.
class Child extends React.Component {
constructor(props){
super(props);
this.updateState = this.updateState.bind(this);
}
updateState() { // call this onClick to trigger the update
if (somecondition) {
// doing some redux store update
this.props.reloadApp();
}
}
render() {
return <button onClick={this.updateState} />;
}
}

Same error but different scenario
tl;dr wrapping state update in setTimeout fixes it.
This scenarios was causing the issue which IMO is a valid use case.
const [someState, setSomeState] = useState(someValue);
const doUpdate = useRef((someNewValue) => {
setSomeState(someNewValue);
}).current;
return (
<SomeComponent onSomeUpdate={doUpdate} />
);
fix
const [someState, setSomeState] = useState(someValue);
const doUpdate = useRef((someNewValue) => {
setTimeout(() => {
setSomeState(someNewValue);
}, 0);
}).current;
return (
<SomeComponent onSomeUpdate={doUpdate} />
);

In my case I had missed the arrow function ()=>{}
Instead of onDismiss={()=>{/*do something*/}}
I had it as onDismiss={/*do something*/}

I had same issue after upgrading react and react native, i just solved that issue by putting my props.navigation.setOptions to in useEffect. If someone is facing same problen that i had i just want to suggest him put your state changing or whatever inside useEffect

Commented some lines of code, but this issue is solvable :) This warnings occur because you are synchronously calling reloadApp inside other class, defer the call to componentDidMount().
import React from "react";
export default class App extends React.Component {
reloadHandler = () => {
console.log("[App] reloadComponent");
// this.props.onShowSpinner();
// this.props.onRefresh();
};
render() {
return <Child reloadApp={this.reloadHandler} />;
}
}
class Child extends React.Component {
static getDerivedStateFromProps(props, state) {
// if (somecondition) {
// doing some redux store update
props.reloadApp();
// }
}
componentDidMount(props) {
if (props) {
props.reloadApp();
}
}
render() {
return <h1>This is a child.</h1>;
}
}

I got this error using redux to hold swiperIndex with react-native-swiper
Fixed it by putting changeSwiperIndex into a timeout

I got the following for a react native project while calling navigation between screens.
Warning: Cannot update a component from inside the function body of a different component.
I thought it was because I was using TouchableOpacity. This is not an issue of using Pressable, Button, or TouchableOpacity. When I got the error message my code for calling the ChatRoom screen from the home screen was the following:
const HomeScreen = ({navigation}) => {
return (<View> <Button title = {'Chats'} onPress = { navigation.navigate('ChatRoom')} <View>) }
The resulting behavior was that the code gave out that warning and I couldn't go back to the previous HomeScreen and reuse the button to navigate to the ChatRoom. The solution to that was doing the onPress in an inline anonymous function.
onPress{ () => navigation.navigate('ChatRoom')}
instead of the previous
onPress{ navigation.navigate('ChatRoom')}
so now as expected behavior, I can go from Home to ChatRoom and back again with a reusable button.
PS: 1st answer ever in StackOverflow. Still learning community etiquette. Let me know what I can improve in answering better. Thanx

If you want to invoke some function passed as props automatically from child component then best place is componentDidMount lifecycle methods in case of class components or useEffect hooks in case of functional components as at this point component is fully created and also mounted.

I was running into this problem writing a filter component with a few text boxes that allows the user to limit the items in a list within another component. I was tracking my filtered items in Redux state. This solution is essentially that of #Rajnikant; with some sample code.
I received the warning because of following. Note the props.setFilteredItems in the render function.
import {setFilteredItems} from './myActions';
const myFilters = props => {
const [nameFilter, setNameFilter] = useState('');
const [cityFilter, setCityFilter] = useState('');
const filterName = record => record.name.startsWith(nameFilter);
const filterCity = record => record.city.startsWith(cityFilter);
const selectedRecords = props.records.filter(rec => filterName(rec) && filterCity(rec));
props.setFilteredItems(selectedRecords); // <-- Danger! Updates Redux during a render!
return <div>
<input type="text" value={nameFilter} onChange={e => setNameFilter(e.target.value)} />
<input type="text" value={cityFilter} onChange={e => setCityFilter(e.target.value)} />
</div>
};
const mapStateToProps = state => ({
records: state.stuff.items,
filteredItems: state.stuff.filteredItems
});
const mapDispatchToProps = { setFilteredItems };
export default connect(mapStateToProps, mapDispatchToProps)(myFilters);
When I ran this code with React 16.12.0, I received the warning listed in the topic of this thread in my browser console. Based on the stack trace, the offending line was my props.setFilteredItems invocation within the render function. So I simply enclosed the filter invocations and state change in a useEffect as below.
import {setFilteredItems} from './myActions';
const myFilters = props => {
const [nameFilter, setNameFilter] = useState('');
const [cityFilter, setCityFilter] = useState('');
useEffect(() => {
const filterName = record => record.name.startsWith(nameFilter);
const filterCity = record => record.city.startsWith(cityFilter);
const selectedRecords = props.records.filter(rec => filterName(rec) && filterCity(rec));
props.setFilteredItems(selectedRecords); // <-- OK now; effect runs outside of render.
}, [nameFilter, cityFilter]);
return <div>
<input type="text" value={nameFilter} onChange={e => setNameFilter(e.target.value)} />
<input type="text" value={cityFilter} onChange={e => setCityFilter(e.target.value)} />
</div>
};
const mapStateToProps = state => ({
records: state.stuff.items,
filteredItems: state.stuff.filteredItems
});
const mapDispatchToProps = { setFilteredItems };
export default connect(mapStateToProps, mapDispatchToProps)(myFilters);
When I first added the useEffect I blew the top off the stack since every invocation of useEffect caused state change. I had to add an array of skipping effects so that the effect only ran when the filter fields themselves changed.

I suggest looking at video below. As the warning in the OP's question suggests, there's a change detection issue with the parent (Parent) attempting to update one child's (Child 2) attribute prematurely as the result of another sibling child's (Child 1) callback to the parent. For me, Child 2 was prematurely/incorrectly calling the passed in Parent callback thus throwing the warning.
Note, this commuincation workflow is only an option. I personally prefer exchange and update of data between components via a shared Redux store. However, sometimes it's overkill. The video suggests a clean alternative where the children are 'dumb' and only converse via props mand callbacks.
Also note, If the callback is invoked on an Child 1 'event' like a button click it'll work since, by then, the children have been updated. No need for timeouts, useEffects, etc. UseState will suffice for this narrow scenario.
Here's the link (thanks Masoud):
https://www.youtube.com/watch?v=Qf68sssXPtM

In react native, if you change the state yourself in the code using a hot-reload I found out I get this error, but using a button to change the state made the error go away.
However wrapping my useEffect content in a :
setTimeout(() => {
//....
}, 0);
Worked even for hot-reloading but I don't want a stupid setTimeout for no reason so I removed it and found out changing it via code works just fine!

I was updating state in multiple child components simultaneously which was causing unexpected behavior. replacing useState with useRef hook worked for me.

Try to use setTimeout,when I call props.showNotification without setTimeout, this error appear, maybe everything run inTime in life circle, UI cannot update.
const showNotifyTimeout = setTimeout(() => {
this.props.showNotification();
clearTimeout(showNotifyTimeout);
}, 100);

How to add event to react function and re-render function

I have a function that renders content to page based on a state populated by API data, but I need to have an onClick event to refine that content;
So currently getPosts returns information from the state 'posts' which is provided with data from our API, but i want to filter this content further, so my idea is to have some sort of event listener, and if actioned, change the data coming out of getPosts.
constructor() {
super();
this.state = {
posts: ""
}
this.getPosts = this.getPosts.bind(this);
}
async componentWillMount(){
var data = await api.posts();
this.setState({posts: data.data});
console.log(this.state.posts);
}
getPosts(type){
if(this.state.posts.length){
return this.state.posts.map((content,index) => {
var url = content.Title.replace(/[^\w\s]/gi, '');
url = url.replace(/\s+/g, '-').toLowerCase();
if(type === content.PostType){
//output something different
}
else{
return(
<Col md={4} className="mb-4" key={index}>
{content.title}
</Col>
);
}
})
}
}
render() {
return (
<div>
<p><button onClick={()=>{this.getPosts('blog')}}>blog</button> <button onClick={()=>{this.getPosts('news')}}>news</button></p>
{this.getPosts()}
</div>
)
}
So my getPosts works fine without any type, how to do tell it to re-output the function on the page based in the onClick event?

Without getting into the complexities of context and keys, a component requires a change in props or state to re-render. To read more about state and component life-cycle, the docs have a great explanation for class components.
Your component does not re-render after the onClick event handler's call to getPosts because getPosts does not update internal component state. getPosts works within render because those values are being returned to React. By using getPosts as an onClick event handler, you are creating React elements and trying to return them to the window.
What follows should be treated as psuedo code that shows how to trigger your component to render different posts:
Consider adding another key to state in your constructor,
constructor(props) {
super(props);
this.state = {
posts: "",
type: null
};
this.getPosts = this.getPosts.bind(this);
this.onClick = this.onClick.bind(this);
}
and creating a click handler that doesn't try to return React elements
function onClick(evt) {
this.setState({ type: evt.target.value });
}
and values to your buttons
<button onClick={this.onClick} type="button" value="blog">blog</button>
Now your button will update state with your new post type, causing your component to re-render:
render() {
return (
<div>
<p>
<button onClick={this.onClick} type="button" value="blog">blog</button>
<button onClick={this.onClick} type="button" value="news">news</button>
</p>
{this.getPosts()}
</div>
);
}
With the content type being stored in state, you can now implement your getPosts call in any way that works for you. Good luck!
It strays from the question asked, but it is worth noting componentWillMount is being deprecated, and componentDidMount is a preferable life-cycle function for side-effects and asynchronous behavior. Thankfully, the documentation has lots of details!

Ok so you should start by changing your default this.state to
this.state = {
posts: []
}
remember that you want to iterate over an array of data instead of iterate a string, that will throw an error if you do that, so better keep from the beginning the data type you want to use.
Then you need to separate the responsibility for your getPosts method, maybe getPostByType is a better name for that, so you have
getPostByType(type) {
// if type is same as content.PostType then return it;
const nextPosts = this.state.posts.filter((content) => type === content.PostType);
this.setState({ posts: nextPosts });
}
and finally you can iterate over posts, like this
render() {
// better use content.id if exists instead of index, this is for avoid problems
// with rerender when same index key is applied.
const posts = this.state.posts.map((content, index) => (
<Col md={4} className="mb-4" key={content.id || index}>
{content.title}
</Col>
));
return (
<div>
<button onClick={() => this.getPostByType('blog')}>Show Blog Posts</button>
{posts}
</div>
);
}
Then you can use getPostsByType any time in any click event passing the type that you want to render.

React setState re-render

First of all, I'm really new into React, so forgive my lack of knowledge about the subject.
As far as I know, when you setState a new value, it renders again the view (or parts of it that needs re-render).
I've got something like this, and I would like to know if it's a good practice or not, how could I solve this kind of issues to improve, etc.
class MyComponent extends Component {
constructor(props) {
super(props)
this.state = {
key: value
}
this.functionRender = this.functionRender.bind(this)
this.changeValue = this.changeValue.bind(this)
}
functionRender = () => {
if(someParams !== null) {
return <AnotherComponent param={this.state.key} />
}
else {
return "<span>Loading</span>"
}
}
changeValue = (newValue) => {
this.setState({
key: newValue
})
}
render() {
return (<div>... {this.functionRender()} ... <span onClick={() => this.changeValue(otherValue)}>Click me</span></div>)
}
}
Another component
class AnotherComponent extends Component {
constructor (props) {
super(props)
}
render () {
return (
if (this.props.param === someOptions) {
return <div>Options 1</div>
} else {
return <div>Options 2</div>
}
)
}
}
The intention of the code is that when I click on the span it will change the key of the state, and then the component <AnotherComponent /> should change because of its parameter.
I assured that when I make the setState, on the callback I throw a console log with the new value, and it's setted correctly, but the AnotherComponent doesn't updates, because depending on the param given it shows one thing or another.
Maybe I need to use some lifecycle of the MyComponent?
Edit
I found that the param that AnotherComponent is receiving it does not changes, it's always the same one.

I would suggest that you'll first test it in the parent using a simple console.log on your changeValue function:
changeValue = (newValue) => {
console.log('newValue before', newValue);
this.setState({
key: newValue
}, ()=> console.log('newValue after', this.state.key))
}
setState can accept a callback that will be invoked after the state actually changed (remember that setState is async).
Since we can't see the entire component it's hard to understand what actually goes on there.
I suspect that the newValue parameter is always the same but i can't be sure.
It seems like you're missing the props in AnotherComponent's constructor. it should be:
constructor (props) {
super(props) // here
}
Try replacing the if statement with:
{this.props.param === someOptions? <div>Options 1</div>: <div>Options 2</div>}
also add this function to see if the new props actually get to the component:
componentWillReceiveProps(newProps){
console.log(newProps);
}
and check for the type of param and someOptions since you're (rightfully) using the === comparison.

First, fat arrow ( => ) autobind methods so you do not need to bind it in the constructor, second re-renders occur if you change the key of the component.
Ref: https://reactjs.org/docs/lists-and-keys.html#keys

"Cannot update during an existing state transition" error in React

I'm trying to do Step 15 of this ReactJS tutorial: React.js Introduction For People Who Know Just Enough jQuery To Get By
The author recommends the following:
overflowAlert: function() {
if (this.remainingCharacters() < 0) {
return (
<div className="alert alert-warning">
<strong>Oops! Too Long:</strong>
</div>
);
} else {
return "";
}
},
render() {
...
{ this.overflowAlert() }
...
}
I tried doing the following (which looks alright to me):
// initialized "warnText" inside "getInitialState"
overflowAlert: function() {
if (this.remainingCharacters() < 0) {
this.setState({ warnText: "Oops! Too Long:" });
} else {
this.setState({ warnText: "" });
}
},
render() {
...
{ this.overflowAlert() }
<div>{this.state.warnText}</div>
...
}
And I received the following error in the console in Chrome Dev Tools:
Cannot update during an existing state transition (such as within render or another component's constructor). Render methods should be
a pure function of props and state; constructor side-effects are an
anti-pattern, but can be moved to componentWillMount.
Here's a JSbin demo. Why won't my solution work and what does this error mean?

Your solution does not work because it doesn't make sense logically. The error you receive may be a bit vague, so let me break it down. The first line states:
Cannot update during an existing state transition (such as within render or another component's constructor).
Whenever a React Component's state is updated, the component is rerendered to the DOM. In this case, there's an error because you are attempting to call overflowAlert inside render, which calls setState. That means you are attempting to update state in render which will in then call render and overflowAlert and update state and call render again, etc. leading to an infinite loop. The error is telling you that you are trying to update state as a consequence of updating state in the first place, leading to a loop. This is why this is not allowed.
Instead, take another approach and remember what you're trying to accomplish. Are you attempting to give a warning to the user when they input text? If that's the case, set overflowAlert as an event handler of an input. That way, state will be updated when an input event happens, and the component will be rerendered.

Make sure you are using proper expression. For example, using:
<View onPress={this.props.navigation.navigate('Page1')} />
is different with
<View onPress={ () => this.props.navigation.navigate('Page1')} />
or
<View onPress={ () => {
this.props.navigation.navigate('Page1')
}} />
The two last above are function expression, the first one is not. Make sure you are passing function object to function expression () => {}

Instead of doing any task related to component in render method do it after the update of component
In this case moving from Splash screen to another screen is done only after the componentDidMount method call.
import React, { Component } from 'react';
import {
StyleSheet,
Text,
View,
Button,
Image,
} from 'react-native';
let timeoutid;
export default class Splash extends Component {
static navigationOptions = {
navbarHidden: true,
tabBarHidden: true,
};
constructor(props) {
super(props)
this.state = { navigatenow: false };
}
componentDidMount() {
timeoutid=setTimeout(() => {
this.setState({ navigatenow: true });
}, 5000);
}
componentWillUnmount(){
clearTimeout(timeoutid);
}
componentDidUpdate(){
const { navigate,goBack } = this.props.navigation;
if (this.state.navigatenow == true) {
navigate('Main');
}
}
render() {
//instead of writing this code in render write this code in
componenetDidUdpate method
/* const { navigate,goBack } = this.props.navigation;
if (this.state.navigatenow == true) {
navigate('Main');
}*/
return (
<Image style={{
flex: 1, width: null,
height: null,
resizeMode: 'cover'
}} source={require('./login.png')}>
</Image>
);
}
}

Call the component props at each time as new render activity. Warning occurred while overflow the single render.
instead of
<Item onPress = { props.navigation.toggleDrawer() } />
try like
<Item onPress = {() => props.navigation.toggleDrawer() } />

You can also define the function overflowAlert: function() as a variable like so and it will not be called immediately in render
overflowAlert = ()=>{//.....//}