如何检测 Ionic 4 的离子含量组件中的滚动已结束？

Question

在 Ionic v3 ion-content 中，有像“scrollTop”这样的属性。在 Ionic v4 中不再有这些属性......我如何确定用户是否到达了内容的末尾？

https://ionicframework.com/docs/v3/api/components/content/Content/ https://ionicframework.com/docs/api/content

Answer 1

这些功能仍然可用，只是位于不同的位置。

使用 启用它后scrollEvents，您需要使用该ionScroll事件，然后根据getScrollElement()函数的结果计算高度，而不是ion-content具有固定窗口高度的 - 。

我在下面写了一个例子。您可以删除console.log's 并将其收紧一点，我只是将它们留在里面以帮助您了解发生了什么。

示例页面：

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

<ion-content [scrollEvents]="true" (ionScroll)="logScrolling($event)">
  <p *ngFor="let dummy of ' '.repeat(75).split('')">Lorem ipsum dolor sit amet consectetur adipisicing elit. Quia placeat nam sapiente iusto eligendi</p>
</ion-content>

示例代码：

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

@Component({
  selector: 'app-detect-scroll-to-bottom',
  templateUrl: './detect-scroll-to-bottom.page.html',
  styleUrls: ['./detect-scroll-to-bottom.page.scss'],
})
export class DetectScrollToBottomPage implements OnInit {

  private scrollDepthTriggered = false;

  constructor() { }

  ngOnInit() {
  }

  async logScrolling($event) {
    // only send the event once
    if(this.scrollDepthTriggered) {
      return;
    }

    console.log($event);

    if($event.target.localName != "ion-content") {
      // not sure if this is required, just playing it safe
      return;
    }

    const scrollElement = await $event.target.getScrollElement();
    console.log({scrollElement});

    // minus clientHeight because trigger is scrollTop
    // otherwise you hit the bottom of the page before 
    // the top screen can get to 80% total document height
    const scrollHeight = scrollElement.scrollHeight - scrollElement.clientHeight;
    console.log({scrollHeight});

    const currentScrollDepth = $event.detail.scrollTop;
    console.log({currentScrollDepth});

    const targetPercent = 80;

    let triggerDepth = ((scrollHeight / 100) * targetPercent);
    console.log({triggerDepth});

    if(currentScrollDepth > triggerDepth) {
      console.log(`Scrolled to ${targetPercent}%`);
      // this ensures that the event only triggers once
      this.scrollDepthTriggered = true;
      // do your analytics tracking here
    }
  }

}

示例日志：