ListView ScrollViewer问题

我认为您正在寻找的实际上是一种ListView 将元素滚动到的顶部的方法。

ScrollViewer 我创建了一个扩展方法是滚动到内的特定元素。

首先 ScrollViewer ，我需要找到 ListView 此类项目的实际实例，或滚动到next ListViewItem 。

ScrollViewer 这是获得的扩展方法：。

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;
}

ScrollViewer 我创建了两个扩展方法，以基于例如索引或链接对象滚动到某个项目。 ListView 并共享GridView 相同的基类 ListViewBase。这两种扩展方法 GridView 也适用。。

更新

基本上，该方法首先找到渲染的项目，然后立即滚动。如果该项为 null ，则表示已启用虚拟化并且尚未实现该项。ScrollIntoViewAsync 打电话给我们首先实现该项目。（与ScrollIntoView 包装内置的基于任务的方法 ChangeViewAsync相同（提供了更简洁的代码））计算并存储位置。现在您知道要滚动的位置了，您必须首先立即将项目滚动回到上一个位置（即无动画），然后使用动画滚动到所需的位置。

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;
    }
}

没有动画的更简单方法

ScrollIntoView 您还可以对第二个参数使用新的重载，以使该项目与顶部边缘对齐。但是，这不会导致以前的扩展方法中的平滑滚动过渡。

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

二

ScrollIntoView使该项进入视图，并且不会滚动到句点。

当您呼叫成员并位于显示列表的底部时，该项向下滚动，直到您成为显示列表的最后一个成员。

当您呼叫成员并位于列表顶部时，该项目将向上滚动，直到您成为列表的第一个成员。

如果我呼叫了一个成员并且当前显示该成员，则根本不起作用。

三

Var sv = new ScrollViewerHelper().GetScrollViewer(listView);
        sv.UpdateLayout();
        sv.ChangeView(0, sv.ExtentHeight, null);

GetScrollViewer方法：


public ScrollViewer GetScrollViewer(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;
    }

ListView ScrollViewer问题

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