cordova – 添加滚动到顶部按钮(Ionic 2 | Typescript)

大家好我想添加“滚动到顶部按钮”.实现以下内容：

1.当用户向下滚动时显示按钮.
2.当用户向上滚动时隐藏按钮.
3.如果点击按钮,则滚动到顶部并隐藏按钮.
有关如何正确的方式的任何建议？

非常感谢

Plunker Demo

要完成这项工作,您需要：

>创建一个将scroll-content元素滚动到顶部的函数
>跟踪滚动内容的滚动位置
>滚动到顶部按钮时使用* ngIf,以在滚动内容达到特定阈值后有条件地显示.

滚动到顶部功能

我调整了this SO answer以应用于scroll-content元素

scrollToTop(scrollDuration) {
let scrollStep = -this.ionScroll.scrollTop / (scrollDuration / 15);
let scrollInterval = setInterval( () => {
    if ( this.ionScroll.scrollTop != 0 ) {
        this.ionScroll.scrollTop = this.ionScroll.scrollTop + scrollStep;
    } else {
      clearInterval(scrollInterval);
    }
}, 15);

跟踪滚动内容位置

此示例使用窗口高度作为显示滚动到顶部按钮的阈值,如下所示：

this.ionScroll.addEventListener("scroll", () => {
  if (this.ionScroll.scrollTop > window.innerHeight) {
    this.showButton = true;
  } else {
    this.showButton = false;
  }
});

按钮Html

<button *ngIf="showButton" (click)="scrollToTop(1000)">Scroll Top</button>

完整组件打字稿

import { NavController } from 'ionic-angular/index';
import { Component, OnInit, ElementRef } from "@angular/core";

@Component({
  templateUrl:"home.html"
})
export class HomePage implements OnInit {
  public ionScroll;
  public showButton = false;
  public contentData = [];

  constructor(public myElement: ElementRef) {}

  ngOnInit() {
    // Ionic scroll element
    this.ionScroll = this.myElement.nativeElement.children[1].firstChild;
    // On scroll function
    this.ionScroll.addEventListener("scroll", () => {
      if (this.ionScroll.scrollTop > window.innerHeight) {
        this.showButton = true;
      } else {
        this.showButton = false;
      }
    });
    // Content data
    for (let i = 0; i < 301; i++) {
      this.contentData.push(i);
    }
  }
  // Scroll to top function
  // Adapted from https://stackoverflow.com/a/24559613/5357459
  scrollToTop(scrollDuration) {
    let scrollStep = -this.ionScroll.scrollTop / (scrollDuration / 15);
    let scrollInterval = setInterval( () => {
        if ( this.ionScroll.scrollTop != 0 ) {
            this.ionScroll.scrollTop = this.ionScroll.scrollTop + scrollStep;
        } else {
          clearInterval(scrollInterval);
        }
    }, 15);
  }

}

完整组件Html

<ion-navbar primary *navbar>
  <ion-title>
    Ionic 2
  </ion-title>
  <button *ngIf="showButton" (click)="scrollToTop(1000)">Scroll Top</button>
</ion-navbar>

<ion-content class="has-header" #testElement>
  <div padding style="text-align: center;">
    <h1>Ionic 2 Test</h1>
    <div *ngFor="let item of contentData">
      test content-{{item}}
    </div>
  </div>
</ion-content>