我有一个包含20个项目的Listview，我想通过编程的方式滚动Listview。
ListView?.ScrollIntoView(ListView.Items[0])
将滚动ListView到第一项。
ListView?.ScrollIntoView(ListView.Items.Count - 1)
使用该函数可以将列表滚动到页面底部。
但是，我无法使用相同的功能将列表滚动到中间的某个项目。
Eg: ListView?.ScrollIntoView(ListView.Items[5])
应该滚动并把我带到列表的第五项。但是实际上它把我带到了列表的第一项。
如果能通过某些解决方法实现这种行为那就太好了？
我认为你正在寻找的是一种方法来实际滚动元素到ListView的顶部。
在这篇文章中，我创建了一个扩展方法，用于在ScrollViewer内滚动到特定元素。
在你的情况下，思路是相同的。
你需要先找到ListView中的ScrollViewer实例，然后找到要滚动到的实际项，即ListViewItem。
这里是一个获取ScrollViewer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实例，我创建了两个扩展方法，分别基于索引或附加对象滚动到一个项目。由于ListView和GridView共享相同的基类ListViewBase，所以这两个扩展方法也适用于GridView。
null，则表示启用了虚拟化，并且尚未实现该项。因此，要先实现该项，请调用ScrollIntoViewAsync（基于任务的方法来包装内置的ScrollIntoView，与ChangeViewAsync相同，提供更清晰的代码），计算位置并保存它。由于现在我知道要滚动到的位置，所以我需要先将该项全部回滚到其先前的位置即时地（即没有动画），然后最终使用动画滚动到期望的位置。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;
}
}
您还可以使用ScrollIntoView的新重载，通过指定第二个参数来确保项目与顶部对齐; 然而，这样做没有我之前的扩展方法中的平滑滚动转换。
MyListView?.ScrollIntoView(MyListView.Items[5], ScrollIntoViewAlignment.Leading);
ScrollIntoView只是将项目带入视野，它不会滚动到一行。
如果您在成员上调用它，并且它在可见列表的底部以下，则向下滚动，直到该项成为可见列表中的最后一个成员。
如果您在成员上调用它，并且它在列表的顶部以上，则向上滚动，直到该项成为列表中的第一个成员。
如果您在成员上调用它并且它当前可见，则根本不执行任何操作。
var sv = new ScrollViewerHelper().GetScrollViewer(listView);
sv.UpdateLayout();
sv.ChangeView(0, sv.ExtentHeight, null);
还有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;
}
致代码所有者的荣誉
试试这个：
listView.SelectedIndex = i;
SemanticZoomLocation location = new SemanticZoomLocation {
Item = listView.SelectedItem
};
listView.MakeVisible(location);
或者滚动到中间位置，不选择任何项目：
SemanticZoomLocation location = new SemanticZoomLocation {
Item = listView.Items[listView.Items.Count / 2]
};
listView.MakeVisible(location);