Navigating to a specific item in a ListView on Ionic 2 by utilizing the ScrollTo feature

Question

Navigating to a specific item in a ListView on Ionic 2 by utilizing the ScrollTo feature

Is there a way to specifically scroll to an item in a listview using Ionic 2? In my app, I have a listview that is connected to an array.

export class TestPage {
    @ViewChild(Content) content: Content;
    public items: Array<Object> = [];

    ionViewWillEnter() {
        console.log(this.navParams.data);
        this.customService.getArray(this.params.index).then((items) => {
            this.items = items;
                //scroll to item
                // this.content.scrollTo()
        });
     }
}

Below is the view:

<ion-list [virtualScroll]="items" approxItemHeight="120px" approxItemWidth="100%" 
    class="items-listview list list-md">
  <button class="items-listview-item item item-md" *virtualItem="let item">
    <div class="items-listview-text">
        {{ item.text }}<span>{{item.index}}</span>
    </div>
  </button>
</ion-list>

I noticed that scrollTo only allows scrolling based on position, not the element itself. How can I scroll to a specific listview item (e.g. item number 150)? Is there a way to determine the position of the specific item and pass it to scrollTo?

angular typescript ionic-framework ionic2 ionic3

Answer 1

Answer №1

If you want to assign a unique identifier to each item, you can simply add an id using something like [id]="'item' + item.index". Then in your code, you can easily retrieve the offsetTop by referencing this id:

scrollTo(elementId:string) {
    let yOffset = document.getElementById(elementId).offsetTop;
    this.content.scrollTo(0, yOffset, 4000)
}

Answer 2

If you want to assign a unique identifier to each item, you can simply add an id using something like [id]="'item' + item.index". Then in your code, you can easily retrieve the offsetTop by referencing this id:

scrollTo(elementId:string) {
    let yOffset = document.getElementById(elementId).offsetTop;
    this.content.scrollTo(0, yOffset, 4000)
}

Answer 3

Answer №2

I found a way to scroll to the selected element without having to traverse the DOM. The current accepted answer only scrolled relative to the parent element, so I came up with this solution:

  scrollTo(element:string) {
    let elem = document.getElementById(element);
    var box = elem.getBoundingClientRect();

    var body = document.body;
    var docEl = document.documentElement;

    var scrollTop = window.pageYOffset || docEl.scrollTop || body.scrollTop;
    var clientTop = docEl.clientTop || body.clientTop || 0;
    var top  = box.top +  scrollTop - clientTop;
    var cDim = this.content.getContentDimensions();

    var scrollOffset = Math.round(top) + cDim.scrollTop - cDim.contentTop;

    this.content.scrollTo(0, scrollOffset, 500);
  }

Answer 4

I found a way to scroll to the selected element without having to traverse the DOM. The current accepted answer only scrolled relative to the parent element, so I came up with this solution:

  scrollTo(element:string) {
    let elem = document.getElementById(element);
    var box = elem.getBoundingClientRect();

    var body = document.body;
    var docEl = document.documentElement;

    var scrollTop = window.pageYOffset || docEl.scrollTop || body.scrollTop;
    var clientTop = docEl.clientTop || body.clientTop || 0;
    var top  = box.top +  scrollTop - clientTop;
    var cDim = this.content.getContentDimensions();

    var scrollOffset = Math.round(top) + cDim.scrollTop - cDim.contentTop;

    this.content.scrollTo(0, scrollOffset, 500);
  }

Answer 5

Answer №3

Here is my approach to solve the issue. Initially, assigning a unique identifier to each item in the listview is essential, followed by selecting the ListView.

@ViewChild(VirtualScroll) listView: VirtualScroll;

Subsequently, I implemented a function (shown below) called ScrollTo, which includes a timeout for resizing the listview after scrolling (since I was dynamically adjusting the buffer ratio).

private scrollTo(index: number) {
    let key = '#customIds_' + index;

    let hElement: HTMLElement = this.content._elementRef.nativeElement;
    let element = hElement.querySelector(key);
    element.scrollIntoView();

    //wait until scroll animation completes
    setTimeout(() => {
        //resize it! Otherwise, the bufferRatio will not update
        this.listView.resize();
    }, 500);
}

Finally, I invoked this function with a delay of one second to ensure it runs after the listview has finished loading:

//there must be a delay, or else the content scroll won't navigate properly to the element..like magic!
setTimeout(() => {
    this.scrollTo('someId');
}, 1000);

Answer 6

Here is my approach to solve the issue. Initially, assigning a unique identifier to each item in the listview is essential, followed by selecting the ListView.

@ViewChild(VirtualScroll) listView: VirtualScroll;

Subsequently, I implemented a function (shown below) called ScrollTo, which includes a timeout for resizing the listview after scrolling (since I was dynamically adjusting the buffer ratio).

private scrollTo(index: number) {
    let key = '#customIds_' + index;

    let hElement: HTMLElement = this.content._elementRef.nativeElement;
    let element = hElement.querySelector(key);
    element.scrollIntoView();

    //wait until scroll animation completes
    setTimeout(() => {
        //resize it! Otherwise, the bufferRatio will not update
        this.listView.resize();
    }, 500);
}

Finally, I invoked this function with a delay of one second to ensure it runs after the listview has finished loading:

//there must be a delay, or else the content scroll won't navigate properly to the element..like magic!
setTimeout(() => {
    this.scrollTo('someId');
}, 1000);

Navigating to a specific item in a ListView on Ionic 2 by utilizing the ScrollTo feature

Answer №1

Answer №2

Answer №3

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