rxjs - 使用 rxjs withLatestFrom 函数

Question

尝试执行以下应该执行的代码:

检索用户的所有聊天列表

检索所有这些聊天的最后一条消息

检索所有这些聊天的收件人信息

将所有内容合并为一个数组，其中每个项目都是聊天、最后一条消息和收件人信息的组合

 this.msgService.getUserChatList(this.uid).do((chats) => {
    this.chats = [];
    if (!(chats.length > 0))
      this.loading = false;
    this.getLastMessages$ = this.getLastMessagesForChats(chats);
    this.getRecipients$ = this.getRecipientsForChats(chats);
}).switchMap( chats => Observable.from(chats) ).withLatestFrom(
   this.getLastMessages$,
   this.getRecipients$,
   (chat, lastMessages, recipients) => ({
     chat: chat,
     last: lastMessages[chat['id']],
     recipient: recipients[chat['id']]
    })
).subscribe( chats => {
  console.log('chats ', chats);
  this.chats.push(chats);
  this.loading = false;
});

附加功能

getLastMessagesForChats(chats: any): Observable<any[]> {
    let lastMessages$ = [];
    for (let chat of chats) {
      let obs = this.msgService.getLastMessage(chat.id)
        .map( last => ({chat: chat.id, last: last}) );
      lastMessages$[chat.id] = obs;
    }
    return Observable.from(lastMessages$).merge().toArray();
  }

  getRecipientsForChats(chats: any): Observable<any[]> {
    let recipients$ = [];
    for (let chat of chats) {
      let obs = this.userService.getUserPublicInfo(chat.recipient)
        .map( recipient => ({chat: chat.id, recipient: recipient}) );
      recipients$[chat.id] = obs;
    }
    return Observable.from(recipients$).merge().toArray();
  }

我收到以下错误

Uncaught (in promise): TypeError: Cannot read property 'subscribe' of undefined
    TypeError: Cannot read property 'subscribe' of undefined

我找不到出了什么问题......我试图在以下 JSBIN 中重现

任何的想法？

Answer 1

链条是自下而上构造的。这意味着订单是subscribe() -> withLatestFrom -> switchMap -> do .

所以在 withLatestFrom尝试订阅 getLastMessages$和 getRecipients$他们是 undefined因为只有在从 do() 中发生的源 Observable 传播第一个值之后才分配它们。 .

编辑:

// Execution
getLastMessages$ = Rx.Observable.of(1);
getRecipients$ = Rx.Observable.of(2);
chats = [];

getUserChatList('uC')
  .do( (chats) => {
    getLastMessages$ = getLastMessagesForChats(chats);
    getRecipients$ = getRecipientsForChats(chats);
  } )
  .switchMap( chats => Rx.Observable.from(chats) )
  .withLatestFrom(
    getLastMessages$,
    getRecipients$,
    (chat, lastMessages, recipients) => ({
        chat: chat,
        last: lastMessages[chat['id']],
        recipient: recipients[chat['id']]
      }))
  .subscribe( c => {
    console.log('chats ', c);
    chats.push(c);
  });

http://jsbin.com/sulatar/3/edit?js,console