Windows 10 ScrollIntoView() 不会滚动到列表视图中间的项目

我有一个包含 20 个项目的列表视图。我想以编程方式滚动列表视图。

ListView?.ScrollIntoView(ListView.Items[0])

将滚动列表视图到第一项。

ListView?.ScrollIntoView(ListView.Items.Count - 1)

会将列表视图滚动到页面底部。

但是，我无法使用相同的函数将列表视图滚动到中间的项目。

Eg: ListView?.ScrollIntoView(ListView.Items[5])

应该滚动并带我到列表的第五项。但它却把我带到了列表的第一项。

如果可以通过一些解决方法来实现这种行为，那就太好了？

我认为你正在寻找的是一种实际上的方法scroll一个元素到顶部ListView.

In 这个帖子 https://stackoverflow.com/questions/32190237/how-to-scroll-to-element-in-uwp/32193216#32193216，我创建了一个扩展方法，可以滚动到 a 中的特定元素ScrollViewer.

你的想法是一样的。

您需要首先找到ScrollViewer您的实例中的ListView，然后是要滚动到的实际项目，即ListViewItem.

这是一个扩展方法来获取ScrollViewer.

public static ScrollViewer GetScrollViewer(this DependencyObject element)
{
    if (element is ScrollViewer)
    {
        return (ScrollViewer)element;
    }

    for (int i = 0; i < VisualTreeHelper.GetChildrenCount(element); i++)
    {
        var child = VisualTreeHelper.GetChild(element, i);

        var result = GetScrollViewer(child);
        if (result == null)
        {
            continue;
        }
        else
        {
            return result;
        }
    }

    return null;
}

一旦我得到ScrollViewer例如，我创建了另外两个扩展方法来分别根据其索引或附加对象滚动到项目。自从ListView and GridView共享相同的基类ListViewBase。这两种扩展方法也应该适用于GridView.

Update

基本上，这些方法将首先找到该项目（如果它已经呈现），然后立即滚动到它。如果该项目是null，表示虚拟化已开启，该项目尚未实现。因此，要首先实现该项目，请调用ScrollIntoViewAsync（基于任务的方法来包装内置ScrollIntoView， 与...一样ChangeViewAsync，它提供了更清晰的代码），计算位置并保存它。既然现在我知道要滚动到的位置，我需要首先将项目一直滚动回其先前的位置即刻（即没有动画），然后最后滚动到有动画的所需位置。

public async static Task ScrollToIndex(this ListViewBase listViewBase, int index)
{
    bool isVirtualizing = default(bool);
    double previousHorizontalOffset = default(double), previousVerticalOffset = default(double);

    // get the ScrollViewer withtin the ListView/GridView
    var scrollViewer = listViewBase.GetScrollViewer();
    // get the SelectorItem to scroll to
    var selectorItem = listViewBase.ContainerFromIndex(index) as SelectorItem;

    // when it's null, means virtualization is on and the item hasn't been realized yet
    if (selectorItem == null)
    {
        isVirtualizing = true;

        previousHorizontalOffset = scrollViewer.HorizontalOffset;
        previousVerticalOffset = scrollViewer.VerticalOffset;

        // call task-based ScrollIntoViewAsync to realize the item
        await listViewBase.ScrollIntoViewAsync(listViewBase.Items[index]);

        // this time the item shouldn't be null again
        selectorItem = (SelectorItem)listViewBase.ContainerFromIndex(index);
    }

    // calculate the position object in order to know how much to scroll to
    var transform = selectorItem.TransformToVisual((UIElement)scrollViewer.Content);
    var position = transform.TransformPoint(new Point(0, 0));

    // when virtualized, scroll back to previous position without animation
    if (isVirtualizing)
    {
        await scrollViewer.ChangeViewAsync(previousHorizontalOffset, previousVerticalOffset, true);
    }

    // scroll to desired position with animation!
    scrollViewer.ChangeView(position.X, position.Y, null);
}

public async static Task ScrollToItem(this ListViewBase listViewBase, object item)
{
    bool isVirtualizing = default(bool);
    double previousHorizontalOffset = default(double), previousVerticalOffset = default(double);

    // get the ScrollViewer withtin the ListView/GridView
    var scrollViewer = listViewBase.GetScrollViewer();
    // get the SelectorItem to scroll to
    var selectorItem = listViewBase.ContainerFromItem(item) as SelectorItem;

    // when it's null, means virtualization is on and the item hasn't been realized yet
    if (selectorItem == null)
    {
        isVirtualizing = true;

        previousHorizontalOffset = scrollViewer.HorizontalOffset;
        previousVerticalOffset = scrollViewer.VerticalOffset;

        // call task-based ScrollIntoViewAsync to realize the item
        await listViewBase.ScrollIntoViewAsync(item);

        // this time the item shouldn't be null again
        selectorItem = (SelectorItem)listViewBase.ContainerFromItem(item);
    }

    // calculate the position object in order to know how much to scroll to
    var transform = selectorItem.TransformToVisual((UIElement)scrollViewer.Content);
    var position = transform.TransformPoint(new Point(0, 0));

    // when virtualized, scroll back to previous position without animation
    if (isVirtualizing)
    {
        await scrollViewer.ChangeViewAsync(previousHorizontalOffset, previousVerticalOffset, true);
    }

    // scroll to desired position with animation!
    scrollViewer.ChangeView(position.X, position.Y, null);
}

public static async Task ScrollIntoViewAsync(this ListViewBase listViewBase, object item)
{
    var tcs = new TaskCompletionSource<object>();
    var scrollViewer = listViewBase.GetScrollViewer();

    EventHandler<ScrollViewerViewChangedEventArgs> viewChanged = (s, e) => tcs.TrySetResult(null);
    try
    {
        scrollViewer.ViewChanged += viewChanged;
        listViewBase.ScrollIntoView(item, ScrollIntoViewAlignment.Leading);
        await tcs.Task;
    }
    finally
    {
        scrollViewer.ViewChanged -= viewChanged;
    }
}

public static async Task ChangeViewAsync(this ScrollViewer scrollViewer, double? horizontalOffset, double? verticalOffset, bool disableAnimation)
{
    var tcs = new TaskCompletionSource<object>();

    EventHandler<ScrollViewerViewChangedEventArgs> viewChanged = (s, e) => tcs.TrySetResult(null);
    try
    {
        scrollViewer.ViewChanged += viewChanged;
        scrollViewer.ChangeView(horizontalOffset, verticalOffset, null, disableAnimation);
        await tcs.Task;
    }
    finally
    {
        scrollViewer.ViewChanged -= viewChanged;
    }
}

更简单的方法，但没有动画

您还可以使用新的重载ScrollIntoView通过指定第二个参数来确保项目在顶部边缘对齐；但是，这样做并没有我以前的扩展方法中的平滑滚动过渡。

MyListView?.ScrollIntoView(MyListView.Items[5], ScrollIntoViewAlignment.Leading);