react怎么更新state

classChildrenextendsComponent{
constructor(props){
super(props);
this.state={
a:this.props.a,
b:this.props.b,
treeData:'',
targets:'',
}
}
componentDidMount(){
const{a,b}=this.state
constdata={a,b}
fetch('/Url',{
data
}).then(res=>{
if(res.code===0){
this.setState({
treeData:res.a,
targets:res.b,
})
}els免费云主机、域名e{
message.error(res.errmsg)
}
})
}
test(item1,item2){
constdata={item1,item2}
fetch('/Url',{data}).then(res=>{
if(res.code===0){
this.setState({
treeData:res.a,
targets:res.b,
})
}else{
message.error(res.errmsg)
}
})
}
}
exportdefaultChildren

//父组件调用子组件

classfatherextendsComponent{
constructer(props){
super(props);
this.state={
a:'1',
b:'2',
}
this.myRef
this.test=this.test.bind(this)
}
change(){
const{a,b}=this.state
console.log(this.myRef.test(a,b))//直接调用实例化后的Children组件对象里函数
}
render(){
{this.myRef=inst}}ref={(inst)=>{this.myRef=inst}}/>
点击
}
}

classfatherextendsComponent{
constructer(props){
super(props);
this.state={
a:'1',
b:'2',
data:'',
}
}
getcomposedata(){
const{a,b}=this.state
constdata={a,b}
fetch('/Url',{data}).then(res=>{
if(res.code===0){
this.setState({
data:res.data
})
}else{
message.error(res.errmsg)
}
})
}
render(){

}
}

componentWillReceiveProps(nextProps){
const{data}=this.state
constnewdata=nextProps.data.toString()
if(data.toString()!==newdata){
this.setState({
data:nextProps.data,
})
}
}