使用箭头函数，因为箭头函数指向父作用域，这将是可用的。 (替代绑定技术)

I Just Pass Props from child component to the parent component in react native from the child component is pass this.
 const validate = (text) => {
        console.log(text);
        let reg = /^\w+([\.-]?\w+)*@\w+([\.-]?\w+)*(\.\w\w+)+$/;
        if (reg.test(text) === false) {
          console.log("Email is Not Correct");
        
          ({ onChangeText: text })
          return false;
        }
        else {
          // console.log("Email Correct");
          
          props.onchangex(text)<<----------------------- here pass the value to the parent component
          console.log(props.onchangex(text));
          ({ onChangeText: text })
       

        }

 and in parent component i set this value to the state like this
   <InpE
      onchangex={this.propx}<---------- pass the parent function to the child component
      placeholder="Please Enter Email"
          />

propx=(a)=> {
 this.setState({email:a}) <-------- this gives me error TypeError: this.setState is not a function


       {this.state.email=a} <---------------- this line is setting up the state email variable
        
    }

现在ES6有箭头函数，它真的很有用，如果你真的混淆了bind(这个)表达式，你可以试试箭头函数

我就是这么做的。

componentWillMount() {
        ListApi.getList()
            .then(JsonList => this.setState({ List: JsonList }));
    }

 //Above method equalent to this...
     componentWillMount() {
         ListApi.getList()
             .then(function (JsonList) {
                 this.setState({ List: JsonList });
             }.bind(this));
 }

回调是在不同的上下文中进行的。你需要绑定到这个，以便在回调中访问:

VK.api('users.get',{fields: 'photo_50'},function(data){
    if(data.response){
        this.setState({ //the error happens here
            FirstName: data.response[0].first_name
        });
        console.info(this.state.FirstName);
    }

}.bind(this));

编辑: 看起来你必须绑定init和api调用:

VK.init(function(){
        console.info("API initialisation successful");
        VK.api('users.get',{fields: 'photo_50'},function(data){
            if(data.response){
                this.setState({ //the error happens here
                    FirstName: data.response[0].first_name
                });
                console.info(this.state.FirstName);
            }

        }.bind(this));
    }.bind(this), function(){
    console.info("API initialisation failed");

    }, '5.34');

这主要是反应体、反应体和酶之间的不相容问题。

尝试像我那样安装以下程序来解决问题:

[...]
    "react": "^18.0.0-beta-f320ef88f-20211116",
    "react-dom": "16.14.0",
    "enzyme": "^3.11.0",
    "enzyme-adapter-react-16": "^1.15.6"
[...]

使用箭头函数，因为箭头函数指向父作用域，这将是可用的。 (替代绑定技术)