如何检测离子含量是否具有滚动条? [英] How to detect if ion-content has a scrollbar?

问题描述

我想在有或没有离子含量滚动条时隐藏或显示元素.更具体地说，我想在没有滚动条时显示一个按钮(以在列表中加载更多项目)，并在有滚动条的地方将其隐藏(因此，通过ion-infinite-scroll完成更多项目的加载).

I want to hide or show elements when there is or there isn't a scrollbar on ion-content. More specifically, I want to show a button (to load more items in a list) when there's no scrollbar and hide it where there is a scrollbar (so the loading of more items is done by ion-infinite-scroll).

我的Ionic应用程序也将部署到桌面，因此具有大屏幕的用户最初不会看到滚动条，因此不会触发离子无限滚动.

My Ionic app will also be deployed to the desktop so users with large screens won't initially see a scrollbar and thus ion-infinite-scroll won't be triggered.

以下是演示该问题的演示:

Here's a demo that showcases the issue:

home.page.html

home.page.html

<ion-header>
  <ion-toolbar>
    <ion-title>
      Ionic header
    </ion-title>
  </ion-toolbar>
</ion-header>

<ion-content>
  <div class="ion-padding">
    <p *ngFor="let item of itemList">{{ item }}</p>

    <!-- How to hide this button when ion-content has a scrollbar? -->
    <!-- *ngIf="???" -->
    <ion-button (click)="incrementItemList(5)">Load more items</ion-button>
  </div>

  <ion-infinite-scroll (ionInfinite)="loadMoreItems($event)">
    <ion-infinite-scroll-content loadingSpinner="crescent"></ion-infinite-scroll-content>
  </ion-infinite-scroll>
</ion-content>

<ion-footer>
  <ion-toolbar>
    <ion-title>
      Ionic footer
    </ion-title>
  </ion-toolbar>
</ion-footer>

home.page.ts

home.page.ts

import { Component } from '@angular/core';

@Component({
  selector: 'app-home',
  templateUrl: 'home.page.html',
  styleUrls: ['home.page.scss'],
})
export class HomePage {

  itemList: string[] = [];

  constructor() {}

  ionViewWillEnter() {
    this.incrementItemList(5);
  }

  incrementItemList(times: number) {
    for (let i = 1; i <= times; i++) {
      this.itemList.push(`Lorem ipsum dolor sit amet consectetur adipisicing elit. Quia placeat nam sapiente iusto eligendi`);
    }
  }

  loadMoreItems(event: any) {
    setTimeout(() => {
      this.incrementItemList(15);
      event.target.complete();
    }, 1000);
  }

}

我正在使用Ionic 4.5.0 + Angular.

I'm using Ionic 4.5.0 + Angular.

我尝试使用 getScrollElement ，

I have tried using getScrollElement, scrollHeight, clientHeight, offsetHeight, but with no success.

有什么想法吗?

推荐答案

借助rtpHarry的帖子(谢谢！)，我终于为该用例提出了一个合适的解决方案:

With the help of rtpHarry's post (thanks!), I finally came up with a proper solution for this use case:

home.page.html

home.page.html

<ion-content>
  <div class="ion-padding">
    <p *ngFor="let item of itemList">{{ item }}</p>

    <!--
      '*ngIf' removes the button from the DOM and changes the size of 'ion-content' which
      is problematic in some scenarios so I toggle the visibility CSS property instead
    -->
    <ion-button [style.visibility]="hasScrollbar ? 'hidden' : 'visible'" (click)="incrementItemList(5)">Load more items</ion-button>
  </div>

  <ion-infinite-scroll (ionInfinite)="loadMoreItems($event)">
    <ion-infinite-scroll-content loadingSpinner="crescent"></ion-infinite-scroll-content>
  </ion-infinite-scroll>
</ion-content>

home.page.ts

home.page.ts

import { Component, ViewChild, HostListener } from '@angular/core';
import { IonContent } from '@ionic/angular';

@Component({
  selector: 'app-home',
  templateUrl: 'home.page.html',
  styleUrls: ['home.page.scss'],
})
export class HomePage {

  hasScrollbar = false;

  itemList: string[] = [];

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

  // checks if there's a scrollbar when the user resizes the window or zooms in/out
  @HostListener('window:resize', ['$event'])
  onResize() {
    this.checkForScrollbar();
  }

  constructor() {}

  ionViewWillEnter() {
    this.incrementItemList(5);
  }

  incrementItemList(times: number) {
    for (let i = 1; i <= times; i++) {
      this.itemList.push(`Lorem ipsum dolor sit amet consectetur adipisicing elit. Quia placeat nam sapiente iusto eligendi`);
    }

    this.checkForScrollbar();
  }

  loadMoreItems(event: any) {
    setTimeout(() => {
      this.incrementItemList(15);
      event.target.complete();
    }, 1000);
  }

  async checkForScrollbar() {
    const scrollElement = await this.content.getScrollElement();
    this.hasScrollbar = scrollElement.scrollHeight > scrollElement.clientHeight;
  }

}

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