Newbie to React:
Error
Cannot read property 'value' of undefined
This occurs after I click on one of the Cell components. I'm wanting to print this.tl.state.value to the console.
Parent Component
class App extends Component {
constructor(props) {
super(props);
this.tl = React.createRef();
}
checkForWinner = () => {
console.log("Checking for winner..." + this.tl.state.value);
}
render() {
return (
<div className="App">
<Cell ref={this.tl} winnercheck={this.checkForWinner} />
</div>
);
}
}
Child Component
class Cell extends Component {
constructor(props) {
super(props);
this.state = {
value: "X"
}
}
toggleVal = () => {
this.props.winnercheck();
}
render() {
return (
<div onClick={() => this.toggleVal()}>
{this.state.value}
</div>
);
}
}
To access the value of a ref, you need to use ref.current. In your case, that would be this.tl.current. Read the documentation for more information.
Related
I'm trying to pass additional data through to a component using hookrouter. I'm not sure what I'm doing wrong. I get the error Functions are not valid as React child. This may happen if you return a Component instead of <Component /> from render.
Path: Routes
const routes = {
"/modules/unit/:id": ({ id }) => (page_url) => (
<UnitPage unit_id={id} page_url={page_url} />
)
};
Path: Link within page
<A href={`modules/unit/${id}`} page_url={page_url}>
Unit link
</A>
** UPDATE **
Path UnitPage.jsx
class UnitPage extends React.Component {
constructor(props) {
super(props);
this.state = {};
}
componentDidUpdate() {
console.log("props", this.props);
}
render() {
const { id, page_url } = this.props;
return (
<div>
<p>{id}</p>
<p>{page_url}</p>
</div>
);
}
}
I have a parent class which is using its child to render some Buttons out of the array 'days'. This is working fine so far. I use the handler to pass the handleClick() to the child. This also worked, without the if statement I get the return in console. What is wrong with my code or thinking for the if statement.
It should reply 'Hi 1' if I click on the Button with value days[0] = 1.
Parent:
export default class Parent extends React.Component {
constructor(props) {
super(props);
this.handleClick = this.handleClick.bind(this);
this.state = {
days: [1,2,3]
}
}
handleClick() {
if(this.props.value === 1) {
return console.log('Hi 1')
}
}
render() {
return (
<div>
<div>
{this.state.days.map(item => <ButtonDays handler={ () => this.handleClick()} key={item} value={item} />)}
</div>
</div>
);
}
}
Child:
export default class ButtonDays extends React.Component {
render() {
return (
<Button onClick={this.props.handler}>{this.props.value}</Button>
);
}
}
In the following part of your parent component
handleClick() {
if(this.props.value === 1) {
return console.log('Hi 1')
}
}
You are checking for a props named value, but this props is only defined in your child component.
What you should do instead is passing the clicked value as a param of the handler function.
<Button onClick={() => this.props.handler(this.props.value)}>{this.props.value}</Button>
And then in your parent component:
handleClick(value) {
if(value === 1) {
return console.log('Hi 1')
}
}
How do I call a child component function from the parent component? I've tried using refs but I can't get it to work. I get errors like, Cannot read property 'handleFilterByClass' of undefined.
Path: Parent Component
export default class StudentPage extends React.Component {
constructor(props) {
super(props);
this.state = {
};
}
newStudentUserCreated() {
console.log('newStudentUserCreated1');
this.refs.studentTable.handleTableUpdate();
}
render() {
return (
<div>
<StudentTable
studentUserProfiles={this.props.studentUserProfiles}
ref={this.studentTable}
/>
</div>
);
}
}
Path: StudentTable
export default class StudentTable extends React.Component {
constructor(props) {
super(props);
this.state = {
studentUserProfiles: props.studentUserProfiles,
};
this.handleTableUpdate = this.handleTableUpdate.bind(this);
}
handleTableUpdate = () => (event) => {
// Do stuff
}
render() {
return (
<div>
// stuff
</div>
);
}
}
UPDATE
Path StudentContainer
export default StudentContainer = withTracker(() => {
const addStudentContainerHandle = Meteor.subscribe('companyAdmin.addStudentContainer.userProfiles');
const loadingaddStudentContainerHandle = !addStudentContainerHandle.ready();
const studentUserProfiles = UserProfiles.find({ student: { $exists: true } }, { sort: { lastName: 1, firstName: 1 } }).fetch();
const studentUserProfilesExist = !loadingaddStudentContainerHandle && !!studentUserProfiles;
return {
studentUserProfiles: studentUserProfilesExist ? studentUserProfiles : [],
};
})(StudentPage);
My design here is: component (Child 1) creates a new studentProfile. Parent component is notified ... which then tells component (Child 2) to run a function to update the state of the table data.
I'm paraphrasing the OP's comment here but it seems the basic idea is for a child component to update a sibling child.
One solution is to use refs.
In this solution we have the Parent pass a function to ChildOne via props. When ChildOne calls this function the Parent then via a ref calls ChildTwo's updateTable function.
Docs: https://reactjs.org/docs/refs-and-the-dom.html
Demo (open console to view result): https://codesandbox.io/s/9102103xjo
class Parent extends React.Component {
constructor(props) {
super(props);
this.childTwo = React.createRef();
}
newUserCreated = () => {
this.childTwo.current.updateTable();
};
render() {
return (
<div className="App">
<ChildOne newUserCreated={this.newUserCreated} />
<ChildTwo ref={this.childTwo} />
</div>
);
}
}
class ChildOne extends React.Component {
handleSubmit = () => {
this.props.newUserCreated();
};
render() {
return <button onClick={this.handleSubmit}>Submit</button>;
}
}
class ChildTwo extends React.Component {
updateTable() {
console.log("Update Table");
}
render() {
return <div />;
}
}
I have a React component render method defined as below, which includes passing a prop called onExchangeSelect into the ExchangeList component.
render() {
return (
<div className="ExchangeContainer list-group">
<ExchangeList
exchanges={this.state.exchanges} selected={this.state.selectedExchange}
onExchangeSelect={selectedExchange => this.setState({selectedExchange})}
/>
<ExchangeDetail exchange={this.state.selectedExchange} />
</div>
);
}
Then, in the ExchangeList constructor, when I console.log this.props, there is not a prop called onExchangeSelect which I can call and th.
The intent is to pass a callback function from the top level component to a child component, to be called by the child so as to affect the state of the parent component. The entire top-level class is below:
class ExchangeContainer extends Component {
constructor(props) {
super(props);
this.state = {
exchanges:[
{
name:"binance",
url:"https://bittrex.com"
},
{
name:"bittrex",
url:"https://bittrex.com"
}
],
selectedExchange:"binance"
};
}
render() {
return (
<div className="ExchangeContainer list-group">
<ExchangeList
exchanges={this.state.exchanges} selected={this.state.selectedExchange}
onExchangeSelect={selectedExchange => this.setState({selectedExchange})}
/>
<ExchangeDetail exchange={this.state.selectedExchange} />
</div>
);
}
}
Why is the function not available as a prop in the child component? (below):
class ExchangeList extends Component {
constructor(props) {
super(props);
this.state = {
};
console.log('This props ' + JSON.stringify(this.props))
}
render() {
console.log("EL: " + JSON.stringify(this.props))
const ExItemList = this.props.exchanges.map((exchange) => {
return <ExchangeListItem key={exchange.name} exchange={exchange}
onExchangeSelect={this.props.onExchangeSelect}/>
});
return (
<ul className="col-md-4 list-group bg-light" >
{ExItemList}
</ul>
);
}
}
i would inspect them in dev tools instead of console.log..place break point and check in chrome dev tool.. onExchangeSelect should be available as part of props in child component..
the offical docs says you should bind the method to a property inside the constructor function. you can play around on my codesandbox for the code below
constructor(props) {
super(props);
this.state = {
exchanges: [
{
name: "binance",
url: "https://bittrex.com"
},
{
name: "bittrex",
url: "https://bittrex.com"
}
],
selectedExchange: "binance"
};
// bind "this" to handleOnExchange method
this.handleOnExchange = this.handleOnExchange.bind(this);
}
// method to be bound
handleOnExchange (data) {
this.setState({selectedExchange: data})
}
render() {
const ExchangeList = props => <div />;
const ExchangeDetail = props => <div />;
return (
<div className="ExchangeContainer list-group">
<ExchangeList
exchanges={this.state.exchanges}
selected={this.state.selectedExchange}
// pass the method to a child property (onExchangeSelect)
onExchangeSelect={this.handleOnExchange}
/>
<ExchangeDetail selectedExchange={this.state.selectedExchange} />
</div>
);
}
to use it inside a (class-based) child component, call the method with an arg like this:
this.props.onExchangeSelect(arg)
The reason it can't see it is because you are looking for it in the wrong place. You are looping through the "exchange" props to create a new component so when you reference "this.props.onExchangeSelect", you are not referring the the props passed to the class as you expected but to the exchange object through which you are looping.
To remedy this, consider rewriting the ExchangeContainer component like so:
class ExchangeContainer extends Component {
constructor(props) {
super(props);
this.state = {
exchanges:[
{
name:"binance",
url:"https://bittrex.com"
},
{
name:"bittrex",
url:"https://bittrex.com"
}
],
selectedExchange:"binance"
};
}
setSelectedExchange = (selectedExchange) =>{
this.setState({selectedExchange})
};
render() {
return (
<div className="ExchangeContainer list-group">
<ExchangeList
exchanges={this.state.exchanges} selected={this.state.selectedExchange}
onExchangeSelect={selectedExchange => setSelectedExchange(selectedExchange)}
/>
<ExchangeDetail exchange={this.state.selectedExchange} />
</div>
);
}
}
And the ExchangeList component like so:
class ExchangeList extends Component {
constructor(props) {
super(props);
this.state = {
};
}
render() {
console.log("EL: " + JSON.stringify(this.props));
const {exchanges, selected, onExchangeSelect} = this.props;
const ExItemList = exchanges.map((exchange) => {
return <ExchangeListItem key={exchange.name} exchange={exchange}
onExchangeSelect={onExchangeSelect}/>
});
return (
<ul className="col-md-4 list-group bg-light" >
{ExItemList}
</ul>
);
}
}
I have react component in react native app and this will return Smth like this:
constructor(){
...
this.Comp1 = <Component1 ..... >
this.Comp2 = <Component2 ..... >
}
render(){
let Show = null
if(X) Show = this.Comp1
else Show = this.Comp1
return(
{X}
)
}
and both of my Components have an API request inside it ,
so my problem is when condition is changed and this toggle between Components , each time the Components sent a request to to that API to get same result ,
I wanna know how to save constructed Component which they wont send request each time
One of the ways do that is to handle the hide and show inside each of the child component comp1 and comp2
So you will still render both comp1 and comp2 from the parent component but you will pass a prop to each one of them to tell them if they need to show or hide inner content, if show then render the correct component content, else just render empty <Text></Text>
This means both child components exist in parent, and they never get removed, but you control which one should show its own content by the parent component.
So your data is fetched only once.
Check Working example in react js: https://codesandbox.io/s/84p302ryp9
If you checked the console log you will find that fetching is done once for comp1 and comp2.
Also check the same example in react native below:
class Parent extends Component {
constructor(props)
{
super(props);
this.state={
show1 : true //by default comp1 will show
}
}
toggleChild= ()=>{
this.setState({
show1 : !this.state.show1
});
}
render(){
return (
<View >
<Button onPress={this.toggleChild} title="Toggle Child" />
<Comp1 show={this.state.show1} />
<Comp2 show={!this.state.show1} />
</View>
)
}
}
Comp1:
class Comp1 extends Component
{
constructor(props) {
super(props);
this.state={
myData : ""
}
}
componentWillMount(){
console.log("fetching data comp1 once");
this.setState({
myData : "comp 1"
})
}
render(){
return (
this.props.show ? <Text>Actual implementation of Comp1</Text> : <Text></Text>
)
}
}
Comp2:
class Comp2 extends Component {
constructor(props) {
super(props);
this.state = {
myData2: ""
}
}
componentWillMount() {
console.log("fetching data in comp2 once");
this.setState({
myData2: "comp 2"
});
}
render() {
return (
this.props.show ? <Text>Actual implementation of Comp2</Text> : <Text></Text>
)
}
}
I think, you should move all your logic to the main component (fetching and saving data, so you component1 and component2 are simple dumb components. In component1 and component2 you can check "does component have some data?", if there isn't any data, you can trigger request for that data in parent component.
Full working example here: https://codesandbox.io/s/7m8qvwr760
class Articles extends React.Component {
componentDidMount() {
const { fetchData, data } = this.props;
if (data && data.length) return;
fetchData && fetchData();
}
render() {
const { data } = this.props;
return (
<div>
{data && data.map((item, key) => <div key={key}>{item.title}</div>)}
</div>
)
}
}
class App extends React.Component{
constructor(props){
super(props);
this.state = {
news: [],
articles: [],
isNews: false
}
}
fetchArticles = () => {
const self = this;
setTimeout( () => {
console.log('articles requested');
self.setState({
articles: [{title: 'article 1'}, {title: 'articles 2'}]
})
}, 1000)
}
fetchNews = () => {
const self = this;
setTimeout(() => {
console.log('news requested');
self.setState({
news: [{ title: 'news 1' }, { title: 'news 2' }]
})
}, 1000)
}
handleToggle = (e) => {
e.preventDefault();
this.setState({
isNews: !this.state.isNews
})
}
render(){
const { news, articles, isNews} = this.state;
return (
<div>
<a href="#" onClick={this.handleToggle}>Toggle</a>
{isNews? (
<News data={news} fetchData={this.fetchNews} />
): (
<Articles data={articles} fetchData={this.fetchArticles} />
)}
</div>
)
}
}