如何在 Class 组件的函数内使用 React Context

Question

How can I access objects inside of React Context inside a function of a Class Component.

I've got the following React Component

import StoreContext from '../../context/StoreContext'

class ProductForm extends Component {
  static contextType = StoreContext

  constructor(props) {
    super(props);

  }

  handleOptionChange(event) {

    const test = this.contextType.client.testObject

  }

I've tried accessing the client object inside the context like this but It doesn't work because it says cant read the property of undefined.

I'm wondering where my mistake is.

Answer 1

Change this to context instead of contextType

this.context.client.testObject

ie Your code should look like

import StoreContext from '../../context/StoreContext'

class ProductForm extends Component {
  static contextType = StoreContext

  constructor(props) {
    super(props);

  }

  handleOptionChange(event) {

    const test = this.context.client.testObject

  }

Leave the static propery as context type and access context in methods as using this.context

Answer 2

I would describe using context in a class component in 3 steps

define the context object with a value you want to share with entire app

const StaticBackEditor = React.createContext({isDebug: true})

wrap the entire app this context and set the values

function App() {
    return (
        <Provider store={store}>
            <StaticBackEditor.Provider value={{isDebug: true}}>
                <div className="App">
              <Layout />
        </div>
                </StaticBackEditor.Provider>
            </Provider>
        )

use the value in a component

class Tree extends React.Component<IProps, IState> {
    // this must be named contextType!
    static contextType = StaticBackEditor 
}

// its wired that we need to access a static field through this , but you do!
{this.context.isDebug && <span className="debug">