To make this work you need to:
- Create a function that scrolls your
scroll-content
element to the top
- Track the scroll position of
scroll-content
- Use
*ngIf
on your scroll to top button to conditionally show after scroll-content
has reached a certain threshold.
Scroll to top function
I adapted this SO answer to apply to the scroll-content
element
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);
Track scroll-content
position
This example uses the window height as the threshold for showing the scroll to top button like this:
this.ionScroll.addEventListener("scroll", () => {
if (this.ionScroll.scrollTop > window.innerHeight) {
this.showButton = true;
} else {
this.showButton = false;
}
});
Button Html
<button *ngIf="showButton" (click)="scrollToTop(1000)">Scroll Top</button>
Full component Typescript
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);
}
}
Full component 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>