React: How to read state from within handler function?-CodePudding

I'm new to React working on an existing React component (that appears to be built in an older style - no hooks).

I want to read and set state within a handler function. I have the following code:

export default class MyComponent extends React.Component { 

static defaultProps = {
    data: {}
};

constructor(props) {
     super(props);

     // Other states

     this.state.myState = false;
};

handleMyChange() {
    if (!this.state.myState) {
        console.log("hello world");
    }
}

However I get the error Cannot read properties of undefined.

I've tried various like state.myState but am not really sure what I should be doing.

Can anyone point me in the right direction?

CodePudding user response：

In order to have this context in your function, you will need to bind it in the constructor first

Here is a small example is taken from the official doc:

import React from "react";

export default class SayHello extends React.Component {
  constructor(props) {
    super(props);
    this.state = { message: "Hello!" };
    // This line is important!
    this.handleClick = this.handleClick.bind(this);
  }

  handleClick() {
    alert(this.state.message);
  }

  render() {
    // Because `this.handleClick` is bound, we can use it as an event handler.
    return <button onClick={this.handleClick}>Say hello</button>;
  }
}