Ionic 4 ion-content scroll to bottom

问题

I am creating a chat page using Ionic 4 and I'm trying to make it automatically scroll to the bottom of the page. I did it like this and it's not working:

import { IonContent } from "@ionic/angular";

export class ChatroomPage implements OnInit {
    messageForm: FormGroup;
    messages: any[];
    messenger: any;
    @ViewChild(IonContent) content: IonContent;

    constructor(
        private navExtras: NavExtrasService,
        private api: RestApiService,
        private httpNative: HTTP
    ) { }

    ngOnInit() {
        this.content.scrollToBottom(300);
    }
}

In the html file:

<ion-header>
    <ion-toolbar color="primary">
        <ion-title>Chatroom</ion-title>
            </ion-toolbar>
        </ion-header>

        <!-- display previous message -->
        <ion-content padding id="content"> 

        <ion-list>
            <ion-item *ngFor="let message of messages">
                {{ message.message }}
            </ion-item>
        </ion-list>

        </ion-content>

    <!-- chat message input -->
    <ion-footer>
        <form [formGroup]="messageForm" (submit)="sendMessage()" (keydown.enter)="sendMessage()">
            <ion-input formControlName="message" type="text" placeholder="Enter your message"></ion-input>
            <ion-button type="submit">Send</ion-button>
        </form>
    </ion-footer>

The error displayed is:

ng:///ChatroomPageModule/ChatroomPage_Host.ngfactory.js:5 ERROR TypeError: Cannot read property 'scrollToBottom' of undefined

Please enlighten me what did I do wrong. Most tutorials I found are using Ionic 3 and they use Content from ionic-angular instead of IonContent from @ionic/angular. I cannot seem to use Content in Ionic 4 as it doesn't have the scrollToBottom method.

回答1:

You can reach the bottom of the content with the method scrollToBottom()

scrollToBottom(duration?: number) => Promise<void>

Add an ID to the ion-content

<ion-content #content>
</ion-content>

Get the content ID in .ts and call the scrollToBottom method with a chosen duration

@ViewChild('content') private content: any;

ngOnInit() {
  this.scrollToBottomOnInit();
}

scrollToBottomOnInit() {
  this.content.scrollToBottom(300);
}

https://ionicframework.com/docs/api/content

EDIT:

ViewChild gets the correct data with the provided content ID

@ViewChild('content') private content: any;

ngOnInit vs ionViewDidEnter / ionViewWillEnter

ngOnInit doesn't trigger if you come back from a navigation stack, ionViewWillEnter / ionViewDidEnter will. So if you place the function in ngOnInit, the scrollToBottom won't work if you navigate back.

回答2:

Tomas Vancoillie is right, but when you add new text and add to list, it won't push it up above input text. Therefore to push text to array and update view to bottom again use ngZone.

import { Component, ViewChild,NgZone } from '@angular/core';

In constructor add

public _zone: NgZone

Call your function

this._zone.run(() => {
  setTimeout(() => {
    this.contentchat.scrollToBottom(300);
  });
});

回答3:

Most of your code is fine. You just need to do 2 changes and that should work for you, in Ionic 4. Here are the changes:

Change 1 (HTML FILE):

Replace:

<ion-content padding id="content">

with:

<ion-content padding #content>

Change 2 (TS FILE):

Replace:

scrollToBottomOnInit() {
  this.content.scrollToBottom(300);
}

with:

scrollToBottomOnInit() {
    setTimeout(() => {
        if (this.content.scrollToBottom) {
            this.content.scrollToBottom(400);
        }
    }, 500);
}

NOTE:

If you do not import IonContent (similar to the way you already did), the code will fail to compile and you will see console errors such as this:

ERROR Error: Uncaught (in promise): ReferenceError: Cannot access 'MessagesPageModule' before initialization

where MessagesPageModule is the Module associated with the page that you are trying to implement the feature in.

回答4:

This works for me on December 2019.

.html

<ion-content #content>

</ion-content>

.ts

@ViewChild('content', { static: false }) content: IonContent;

constructor(){}

 ngOnInit(): void {
    this.scrollToBottom();
  }


 scrollToBottom(): void {
    this.content.scrollToBottom(300);
  }

回答5:

Due to recent changes on ionic 4, I found the code in suggested answer no longer works for me. Hope this helps all the new comers.

import { IonContent } from '@ionic/angular';

export class IonicPage implements OnInit {
@ViewChild(IonContent, {read: IonContent, static: false}) myContent: IonContent;

  constructor() {}

  ScrollToBottom(){
    setTimeout(() => {
      this.myContent.scrollToBottom(300);
   }, 1000);

  }
}

No id specified in .html file for < ion-content >

Official documentation refers to ion-content. Ionic version used listed below at the time of this post.

Ionic CLI                     : 5.4.13
Ionic Framework               : @ionic/angular 4.11.3
@angular/cli                  : 8.1.3

来源：https://stackoverflow.com/questions/55116825/ionic-4-ion-content-scroll-to-bottom

标签

angular

typescript

ionic-framework

ionic4