使用 cdk-virtual-scroll (Angular 8) 滚动到底部 [英] Scroll to bottom with cdk-virtual-scroll (Angular 8)

问题描述

目标

显示消息列表并在收到新消息时滚动到底部，即使我在顶部也是如此.即使有不同高度的元素，我也想完全滚动到底部.

问题

使用虚拟滚动，我必须设置 [itemSize] 属性，但对我来说它不是静态值:

• 当一条消息对于一行来说太长时，它会分成多行，因此它的高度会发生变化.
• 我有不同类型的不同高度的消息(例如系统消息).

此外，我使用 ng-content 插入来自父级的按钮以加载以前的消息.我看到的是，当 _scrollToBottom 被调用时，它不是把我带到底部，而是把我带到更高一点.我怀疑这是因为 virtual-scroll 中元素的高度不同.

我已经从 Angular 阅读了这个自动调整滚动策略问题:https://github.com/angular/components/issues/10113; 但我不确定这会解决我的问题.

欢迎任何关于我能做什么的想法.

测试

Codesandbox:https://codesandbox.io/s/angular-virtual-scroll-biwn6

• 加载消息后，向上滚动.
• 发送消息.(当新消息加载时，虚拟滚动不再滚动到底部，而是停得更高一点)
• 重复

有错误的视频:https://gofile.io/d/8NG9HD

---

解决方案

Gourav Garg 给出的解决方案有效.只需执行两次滚动功能即可.

我现在正在这样做:

<预><代码>私人 _scrollToBottom() {setTimeout(() => {this.virtualScrollViewport.scrollTo({底部:0，行为:'自动'，});}, 0);setTimeout(() => {this.virtualScrollViewport.scrollTo({底部:0，行为:'自动'，});}, 50);}

我认为它不是很优雅，但效果很好.

解决方案

如果你正在使用 cdk 可以使用 >7

this.virtualScrollViewport.scrollToIndex(messages.length-1);

因为这将移动到最后一项的顶部.您需要为该项目调用 scrollIntoView.

this.virtualScrollViewport.scrollToIndex(this.numbers.length - 1);setTimeout(() => {const items = document.getElementsByClassName("list-item");items[items.length - 1].scrollIntoView();}, 10);

<cdk-virtual-scroll-viewport #virtualScroll style="height: 500px" itemSize="90"><ng-container *cdkVirtualFor="让 n 个数字"><li class="list-item">{{n}} </li></ng-容器></cdk-virtual-scroll-viewport>

我已经更新了你的 沙盒

Goal

Display a list of messages and scroll to the bottom when a new message is received, even when I am at the top. I would like to scroll fully bottom even with elements of different heights.

Problem

With virtual scroll, I have to set the [itemSize] property, but for me it is not a static value:

• When a message is too long for one line it breaks in multiple, so its height changes.
• I have different types of messages with different heights (system messages for example).

Also, I am using ng-content to insert a button from the parent to load previous messages. What I see is that, when _scrollToBottom is invoked, instead of taking me to the bottom, it takes me to a bit higher. I suspect this is because of the different heights of elements inside virtual-scroll.

I have read this autosize scroll strategy issue from Angular: https://github.com/angular/components/issues/10113; but I am not sure this will solve my problem.

Any idea of what I could do will be welcome.

Test

Codesandbox: https://codesandbox.io/s/angular-virtual-scroll-biwn6

• When messages are loaded, scroll up.
• Send message. (When the new message is loaded, instead of scrolling to bottom, the virtual-scroll stops a little higher)
• Repeat

Video with the error: https://gofile.io/d/8NG9HD

---

Solution

The solution given by Gourav Garg works. Simply by executing twice the scroll function.

I am doing this now:

  private _scrollToBottom() {
    setTimeout(() => {
      this.virtualScrollViewport.scrollTo({
        bottom: 0,
        behavior: 'auto',
      });
    }, 0);
    setTimeout(() => {
      this.virtualScrollViewport.scrollTo({
        bottom: 0,
        behavior: 'auto',
      });
    }, 50);
  }

I think it is not very elegant but works fine.

解决方案

You can use if you are using cdk > 7

this.virtualScrollViewport.scrollToIndex(messages.length-1);

As this will move to the top of last item. You need to call scrollIntoView for that item.

this.virtualScrollViewport.scrollToIndex(this.numbers.length - 1);
setTimeout(() => {
  const items = document.getElementsByClassName("list-item");
  items[items.length - 1].scrollIntoView();
}, 10);

<cdk-virtual-scroll-viewport #virtualScroll style="height: 500px" itemSize="90">
  <ng-container *cdkVirtualFor="let n of numbers">
    <li class="list-item"> {{n}} </li>
  </ng-container>
</cdk-virtual-scroll-viewport>

I have updated your sandbox

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