Angular 错误类型错误：无法读取属性'；未读'；未定义的

当页面第一次加载时，我会不断收到下面的错误，但我可以退出页面，一切都会按预期进行

ERROR TypeError: Cannot read property 'unread' 
of undefined
at listing-element.ts:34
at Array.forEach (<anonymous>)
at SafeSubscriber._next (listing-element.ts:33)
at SafeSubscriber.__tryOrUnsub (Subscriber.js:238)
at SafeSubscriber.next (Subscriber.js:185)
at Subscriber._next (Subscriber.js:125)
at Subscriber.next (Subscriber.js:89)
at MapSubscriber._next (map.js:83)
at MapSubscriber.Subscriber.next (Subscriber.js:89)
at MapSubscriber._next (map.js:83)

---

这是我认为所有相关的信息，但如果有人需要更多信息，我非常乐意提供我能提供的任何信息。

您可以按如下所示进行尝试

this.afAuth.authState.subscribe(
      (auth) => {
        if (auth != null) {
            this.listingProvider.checkUnreadThreads(this.listing.id).subscribe(threads 
               => {
              threads.forEach(thread => {
                if (thread[auth.uid].unread) { // <-Line 34 is here
                  this.unread = true;
                }
              })
            })
          })
        }
      });

this.afAuth.authState.subscribe(
（auth）=>{
如果（auth！=null）{
this.listingProvider.checkUnreadThreads（this.listing.id）.subscribe（threads
=> {
threads.forEach（线程=>{
如果（thread[auth.uid].unread）{/在尝试访问unthread属性之前检查用户是否存在线程。如果您仍然面临此问题，请告诉我

if (thread[this.userId] && thread[this.userId].unread) { 
              this.unread = true;
            }

返回{id，…data}
将把id和所有数据字段合并为一个

现在您的
线程
如下所示

id:....,
unread:....,
fieldx:....,
fieldy:..... etc

试试这个代码

this.userId = this.auth.getUser().uid;
this.listingProvider.checkUnreadThreads(this.listing.id).subscribe(threads => {
      threads.forEach(thread => {
        if (thread.id == this.userId && thread.unread) { 
          this.unread = true;
        }
      })
    })

谢谢，虽然示例本身不起作用，但它确实给了我一个想法，让我尝试将其包装到另一个if语句中，但只使用
thread[this.userId]
作为条件，而不是
thread[this.userId].unread
，并且它不再给我错误！很高兴它有帮助：）
this.userId = this.auth.getUser().uid;
this.listingProvider.checkUnreadThreads(this.listing.id).subscribe(threads => {
      threads.forEach(thread => {
        if (thread.id == this.userId && thread.unread) { 
          this.unread = true;
        }
      })
    })