Uncaught TypeError:无法读取未定义的属性“状态或道具" [英] Uncaught TypeError: Cannot read property 'state or props' of undefined

问题描述

所以我开始将我的应用程序从ES2015转换为使用React的ES6.

So I started converting my application from ES2015 to ES6 which uses React.

我有一个父类和一个子类，

I have a parent class and a child class like so,

export default class Parent extends Component {
    constructor(props) {
        super(props);
        this.state = {
            code: ''
        };
    }

    setCodeChange(newCode) {
        this.setState({code: newCode});
    }


    login() {
        if (this.state.code == "") {
            // Some functionality
        }
    }

    render() {
        return (
            <div>
                <Child onCodeChange={this.setCodeChange} onLogin={this.login} />
            </div>
        );
    }
}

子类，

export default class Child extends Component {
    constructor(props) {
        super(props);
    }

    handleCodeChange(e) {
        this.props.onCodeChange(e.target.value);
    }

    login() {
        this.props.onLogin();
    }

    render() {
        return (
            <div>
                <input name="code" onChange={this.handleCodeChange.bind(this)}/>
            </div>
            <button id="login" onClick={this.login.bind(this)}>
        );
    }
}

Child.propTypes = {
    onCodeChange: React.PropTypes.func,
    onLogin: React.PropTypes.func
};

但这会导致以下错误，

此状态未定义

它指的是

if (this.state.code == "") {
    // Some functionality
}

有什么想法会导致这种情况吗?

Any idea what could be causing this ?

推荐答案

您可以使用箭头功能绑定您的功能.您需要在子组件和父组件中都绑定功能.

You can use arrow function to bind you functions. You need to bind you functions both in child as well as parent components.

父母:

export default class Parent extends Component {
    constructor(props) {
        super(props);
        this.state = {
            code: ''
        };
    }

    setCodeChange = (newCode) => {
        this.setState({code: newCode});
    }


    login = () => {
        if (this.state.code == "") {
            // Some functionality
        }
    }

    render() {
        return (
            <div>
                <Child onCodeChange={this.setCodeChange} onLogin={this.login} />
            </div>
        );
    }
}

孩子

export default class Child extends Component {
    constructor(props) {
        super(props);
    }

    handleCodeChange = (e) => {
        this.props.onCodeChange(e.target.value);
    }

    login = () => {
        this.props.onLogin();
    }

    render() {
        return (
            <div>
                <input name="code" onChange={this.handleCodeChange}/>
            </div>
            <button id="login" onClick={this.login}>
        );
    }
}

Child.propTypes = {
    onCodeChange: React.PropTypes.func,
    onLogin: React.PropTypes.func
};

还有其他绑定功能的方法，例如您正在使用的一种，但您也需要对父级组件进行绑定，例如<Child onCodeChange={this.setCodeChange.bind(this)} onLogin={this.login.bind(this)} />

There are other ways to bind the functions as well such as the one you are using but you need to do that for parent component too as <Child onCodeChange={this.setCodeChange.bind(this)} onLogin={this.login.bind(this)} />

或者您可以在构造函数中将绑定指定为

or you can specify binding in the constructor as

父母:

constructor(props) {
    super(props);
    this.state = {
        code: ''
    };
 this.setCodeChange = this.setCodeChange.bind(this);
 this.login = this.login.bind(this);
}

孩子

constructor(props) {
    super(props);
    this.handleCodeChange = this.handleCodeChange.bind(this);
    this.login = this.login.bind(this);
}

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