react不从firebase呈现数组值,数组长度为0,尽管在控制台上有该值

const getthread=(threadid)=>。{
返回snapshot.val()。

const getthreadlist=(id)=>。{
。然后((快照)=>。{
如果(friends.hasownProperty(key))。{
threadlist.push(线程)
}
}


组件didmount()。{
。然后(threadlist=>){
}


T组件。








 const getThread = (threadID) => {
  return db.ref(`threads/${threadID}`).once('value')
  .then((snapshot)=>{
    return snapshot.val()
  })
}

const getThreadList = (id) => {
  let threadList = []
  return db.ref(`users/${id}/friends`).once('value')
  .then((snapshot)=>{
    let friends = snapshot.val()
    for(let key in friends){
      if(friends.hasOwnProperty(key)) {
        getThread(friends[key].threadID)
        .then((thread)=>{
          threadList.push(thread)
        })
      }
    }
    return threadList
  })
}

class SomeComponent　extends Component{

  componentDidMount(){
    let { id } = this.props
    getThreadList(id)
    .then(threadList => {
      this.setState(() => ({ threadList }))
    })
  }

  render(){

    //value of threadList doses't appear


我怀疑这是由于Promise的误用,所以console.log显示值,但react组件不显示任何内容。但我也怀疑反应方面,无法准确定位问题所在。