javascript - ionic 2 : How do you reinstantiate @ViewChild if you dismiss the view?

Question

我正在创建一种聊天体验，并且该页面通过使用 ionic-angular 上 Content 中的 scrollToBottom 方法来跟上对话。如果我从“PreChat.html”开始并转到“Chat.html”然后我关闭“Chat.html”返回到“PreChat.html”并再次返回到“Chat.html”我收到以下错误: “无法读取 null 的属性‘scrollToBottom’”。体验应该能够在任何时候或重复进入。

PreChat.html:

<ion-content>
  <button (click)="goToChat()" href="#">
    Chat
  </button>
</ion-content>

PreChat.ts:

import { Component } from '@angular/core';
import { ModalController } from 'ionic-angular';
import { Chat } from '../chat';

@Component({
  selector: 'preChat',
  templateUrl: 'preChat.html'
})
export class PreChat  {
   constructor(private modalCtrl: ModalController){}

   goToChat(): any {
    let profileModal = this.modalCtrl.create(Chat);
    profileModal.present();
  }
}

聊天.html:

<ion-content>
  <button ion-button="filter-button"(click)="dismiss()">
    <ion-icon name="close"></ion-icon>
  </button>
  <div *ngFor="let convo of conversationArray">
    <div class="b-text">{{convo.speak}}</div>
  </div>
</ion-content>

聊天.ts:

import { Component, ViewChild } from '@angular/core';
import { Content, Events, ViewController } from 'ionic-angular';

@Component({
  templateUrl: 'Chat.html'
})

export class Chat {
  @ViewChild(Content) content: Content;
  conversationArray: any[] = [];
  constructor(private events: Events, private viewCtrl: ViewController){
    this.events.subscribe('conversation', convo => {
      this.conversationArray = convo;
      this.content.scrollToBottom();
    })
  }
  dismiss() {
   this.viewCtrl.dismiss(); 
 }
}

Answer 1

为此，您必须使用 ionViewDidEnter 页面事件而不是 constructor。

Runs when the page has fully entered and is now the active page. This event will fire, whether it was the first load or a cached page.

ionViewDidEnter() : void {
 this.platform.ready().then(() => { //platform ready
   this.events.subscribe('conversation', convo => {
      this.conversationArray = convo;
      this.content.scrollToBottom();
    })
 })
}