React--class组件

创建Class组件

• ES5

import React from 'react'

cosnt A = React.createClass({
  render(){
    return(
      
 hi 
    )
  }
})

export default A

• ES6

import React from 'react';
class B extends React.Component{
  constructor(props){
    super(props);
  }
  render(){
    return(
      
 hi 
    )
  }
}
export default B;

Props外部数据

• 传入 props给 B 组件

export default class Parent extends React.Component{
  constructor(props){
    super(props)
    this.state = {name:'fanison',n:1}
  }
  onClick = ()=>{
    this.setState((state)=>{
      return {n:state.n + 1}
    })
  }
  render(){
    return  hi 
  }
}

class B extends React.Component{
  constructor(props){
    super(props)      // this.props 就是外部数据对象的地址
  }
  render(){
    return (

        {this.props.children},
        {this.props.name}
        

          {this.props.n}
          +1

        
      
    )
  }
}

• Props的作用

接受外部数据：只能读不能写，外部数据由父组件传递
接受外部函数：在恰当的时机调用该函数(一般是父组件的函数)

State & setState 内部数据

class   B extends React.Component{
  constructor(props){
    super(props);
    this.state = {
      name: 'fanison',age:18
    }
  }
render(){}
}

• 读 State
  this.state.name
• 写State
  this.setState(???,fn)

this.setState(newState,fn)
setState不会立刻改变 this.state，会在当前代码运行完后，再去更新this.state，从而触发UI更新

onClick2 = ()=>{
    this.setState({n:this.state.n + 1})
    console.log(this.state.n)        //2
    this.setState({n:this.state.n + 1})
    console.log(this.state.n)       //2
  }

    onClick3 = ()=>{
      this.setState({n:this.state.n + 1},()=>{
        this.setState({
          n:this.state.n + 1
        })
      })
    }

this.setState((state,props)=> newState,fn)

onClick = ()=>{
  this.setState((state)=>{
    return {n:state.n + 1}
  })
  this.setState((state)=>({n:state.n + 1}))
}