React: Children onclick to change parent's state for re-rendering

Question

I'm really new with react. I'm trying to get the parent to change page displayed depending on the states. I have a button in my sub-component that should send "true" or "false" to the parent component so it knows if to render it or not. I think it should be done with props like this:

this.state = {
   btnNewScreen: this.props.btnNewScreen //true or false
};

But im not getting it to work. Could you give any tips? Here is the full parent - child

parent - maindisplay.js

import React from 'react';
import Mainpage_Addscreen from '../components/subcomponents/mainpage-addscreen';
import Mainpage_Showscreens from '../components/subcomponents/mainpage-showscreens';
//
class MainDisplay extends React.Component {
    constructor() {
        super();
        this.state = {
            btnNewScreen: false //should be this.props.btnNewScreen?
        };
    }

    render() {
        var renderThis;
        if (!this.state.btnNewScreen) {
            renderThis =
                <div>
                    <Mainpage_Addscreen />
                    <Mainpage_Showscreens />
                </div>
        }
        else {
            //renderThis = <AddScreen />
            renderThis =
                <div>
                    <Mainpage_Addscreen />
                    <h3>Change to this when true (button click)</h3>
                </div>
        }
        return (
            <div>
                {renderThis}
            </div>
        );
      }
    }


    export default MainDisplay;

child - mainpage-addscreen.js

import React from 'react';

import Glyphicon from 'react-bootstrap/lib/Glyphicon';
import Button from 'react-bootstrap/lib/Button';

class Mainpage_Addscreen extends React.Component {
    constructor() {
        super();
        this.state = {
            btnNewScreen: true
        };
        this.newScreen = this.newScreen.bind(this);
    }

    newScreen(e) {
        this.setState({ btnNewScreen: !this.state.btnNewScreen });
        console.log(this.state.btnNewScreen);
    }
    render() {
        var text = this.state.btnNewScreen ? 'Add new' : 'Screens';
        return (
            <div className="main_window col-sm-offset-1 col-sm-10">
                <h3 id="addscreens">Screens: </h3>
                <Button id="addScreen" className="btn btn-primary dropdown-toggle" type="button" data-toggle="dropdown" onClick={this.newScreen}><Glyphicon id="refresh_screens" glyph="plus" />&nbsp; {text}</Button>
            </div>
        );
    }
}


export default Mainpage_Addscreen;

Answer 1

What you probably need is a callback function, which your parent passes as a prop to your child, and that your child can then call.

Something like this:

// In parent
constructor() {
  ...
  this.onChildClicked = this.onChildClicked.bind(this);
}

onChildClicked() {
  this.setState({childWasClicked : True });
}

render() {
  ...
  return (
    <div>
      <Child onClicked={this.onChildClicked} />
    </div>
  )
}

// In child
render() {
  ...
  return (
    <div>
      <button onClick={this.props.onClicked} />
    </div>
  )
}

PS: I notice that you have a capitalized <Button> component. This is typically for components that you have defined yourself. Standard DOM elements take lowercase, e.g. <div>, <p> etc

Answer 2

What you need to do is to pass a method from the parent to the child, That it can call when the button is clicked. This method that belongs to the parent will change the state.
In MainPage.js

changeButtonState(event) {
    this.setState({btnNewScreen: !this.state.btnNewScreen})
}

pass this method to your child component as

<Mainpage_Addscreen buttonClick={this.changeButtonState.bind(this)} />

and finally in the child component,

<Button ....   onClick={this.props.buttonClick} />