Question

尝试执行以下代码：

检索用户所有聊天记录的列表
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

将所有项合并为一个数组，其中每个项目都是聊天，上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

我找不到出错的地方......我试图在以下JSBIN

中重现

有什么想法吗？

Answer 1

链条是自下而上构建的。这意味着订单为subscribe() - ＆gt; withLatestFrom - ＆gt; switchMap - ＆gt; do。

因此，在withLatestFrom尝试订阅getLastMessages$和getRecipients$时，它们是undefined，因为只有在第一个值从源Observable传播后才会分配它们这发生在do()。

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

使用rxjs withLatestFrom函数

1 个答案: