WPF - 当 ItemsSource 更改时重置 ListBox 滚动位置

Question

我当前有一个 ListBox，其 ItemsSource 集合绑定到我的视图模型上的 IEnumerable 类型的属性。当该 preoprty 的引用更改时，列表框会按预期更新，但是我遇到一个问题，如果我有大量项目集合并滚动到列表框的底部，然后将引用更改为包含 1 个项目的另一个集合，ListBox 视图为空白且不显示滚动条。然后我必须用鼠标滚轮向上滚动列表框，直到第 1 项进入视图。

因此，我认为我所追求的是一种每当 ItemsSource 属性发生更改时将 ListBox 的滚动位置重置到顶部的方法，这样无论集合有多大或多小，总是会显示某些内容。

Answer 1

我无法重现您的问题（对我来说，更改 ItemsSource 时，ListBox 会滚​​动到新集合中的最后一项）。无论如何，要在每次 ItemsSource 更改时将 ListBox 滚动到顶部，您可以在后面使用一些代码。首先侦听 ItemsSourceProperty 中的更改，然后在生成其项目后将 ListBox 滚动到顶部

更新

创建执行此操作的附加行为而是为了避免代码隐藏。可以像这样使用

<ListBox ...
         behaviors:ScrollToTopBehavior.ScrollToTop="True"/>

ScrollToTopBehavior

public static class ScrollToTopBehavior 
{
    public static readonly DependencyProperty ScrollToTopProperty = 
        DependencyProperty.RegisterAttached 
        (
            "ScrollToTop", 
            typeof(bool),
            typeof(ScrollToTopBehavior),
            new UIPropertyMetadata(false, OnScrollToTopPropertyChanged) 
        );
    public static bool GetScrollToTop(DependencyObject obj) 
    {
        return (bool)obj.GetValue(ScrollToTopProperty); 
    }
    public static void SetScrollToTop(DependencyObject obj, bool value) 
    {
        obj.SetValue(ScrollToTopProperty, value); 
    }
    private static void OnScrollToTopPropertyChanged(DependencyObject dpo, 
                                                     DependencyPropertyChangedEventArgs e) 
    {
        ItemsControl itemsControl = dpo as ItemsControl;
        if (itemsControl != null) 
        {
            DependencyPropertyDescriptor dependencyPropertyDescriptor =
                    DependencyPropertyDescriptor.FromProperty(ItemsControl.ItemsSourceProperty, typeof(ItemsControl));
            if (dependencyPropertyDescriptor != null)
            {
                if ((bool)e.NewValue == true) 
                {
                    dependencyPropertyDescriptor.AddValueChanged(itemsControl, ItemsSourceChanged);
                }
                else 
                {
                    dependencyPropertyDescriptor.RemoveValueChanged(itemsControl, ItemsSourceChanged);
                }
            } 
        } 
    }
    static void ItemsSourceChanged(object sender, EventArgs e)
    {
        ItemsControl itemsControl = sender as ItemsControl;
        EventHandler eventHandler = null;
        eventHandler = new EventHandler(delegate
        {
            if (itemsControl.ItemContainerGenerator.Status == GeneratorStatus.ContainersGenerated)
            {
                ScrollViewer scrollViewer = GetVisualChild<ScrollViewer>(itemsControl) as ScrollViewer;
                scrollViewer.ScrollToTop();
                itemsControl.ItemContainerGenerator.StatusChanged -= eventHandler;
            }
        });
        itemsControl.ItemContainerGenerator.StatusChanged += eventHandler;
    }
}

以及 GetVisualChild 的实现

private T GetVisualChild<T>(DependencyObject parent) where T : Visual
{
    T child = default(T);
    int numVisuals = VisualTreeHelper.GetChildrenCount(parent);
    for (int i = 0; i < numVisuals; i++)
    {
        Visual v = (Visual)VisualTreeHelper.GetChild(parent, i);
        child = v as T;
        if (child == null)
        {
            child = GetVisualChild<T>(v);
        }
        if (child != null)
        {
            break;
        }
    }
    return child;
}

Answer 2

迟到的答案：

一个简单的解决方案是为 TargetUpdated 事件添加事件处理程序，并在 ItemsSource< 上设置 NotifyOnTargetUpdated=True /code> 绑定：

<ListBox x:Name="listBox" 
         ItemsSource="{Binding MySource, NotifyOnTargetUpdated=True}"
         TargetUpdated="ListBox_TargetUpdated"/>

并在事件处理程序中，滚动到顶部项目：

private void ListBox_TargetUpdated(object sender, DataTransferEventArgs e)
{
    if (listBox.Items.Count > 0)
    {
        listBox.ScrollIntoView(listBox.Items[0]);
    }
}

Answer 3

试试这个：

if (listBox.Items.Count > 0) {
    listBox.ScrollIntoView(listBox.Items[0]); 
}

Answer 4

改进了 Fredrik Hedblad 的答案以使用 ObservableCollection：

public static class ItemsControlAttachedProperties
{
    #region ScrollToTopOnItemsSourceChange Property

    public static readonly DependencyProperty ScrollToTopOnItemsSourceChangeProperty =
        DependencyProperty.RegisterAttached(
            "ScrollToTopOnItemsSourceChange",
            typeof(bool),
            typeof(ItemsControlAttachedProperties),
            new UIPropertyMetadata(false, OnScrollToTopOnItemsSourceChangePropertyChanged));

    public static bool GetScrollToTopOnItemsSourceChange(DependencyObject obj)
    {
        return (bool) obj.GetValue(ScrollToTopOnItemsSourceChangeProperty);
    }

    public static void SetScrollToTopOnItemsSourceChange(DependencyObject obj, bool value)
    {
        obj.SetValue(ScrollToTopOnItemsSourceChangeProperty, value);
    }

    static void OnScrollToTopOnItemsSourceChangePropertyChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)
    {
        var itemsControl = obj as ItemsControl;
        if (itemsControl == null)
        {
            throw new Exception("ScrollToTopOnItemsSourceChange Property must be attached to an ItemsControl based control.");
        }

        DependencyPropertyDescriptor descriptor =
            DependencyPropertyDescriptor.FromProperty(ItemsControl.ItemsSourceProperty, typeof(ItemsControl));
        if (descriptor != null)
        {
            if ((bool) e.NewValue)
            {
                descriptor.AddValueChanged(itemsControl, ItemsSourceChanged);
            }
            else
            {
                descriptor.RemoveValueChanged(itemsControl, ItemsSourceChanged);
            }
        }
    }

    static void ItemsSourceChanged(object sender, EventArgs e)
    {
        var itemsControl = sender as ItemsControl;
        DoScrollToTop(itemsControl);

        var collection = itemsControl.ItemsSource as INotifyCollectionChanged;
        if (collection != null)
        {
            collection.CollectionChanged += (o, args) => DoScrollToTop(itemsControl);
        }
    }

    static void DoScrollToTop(ItemsControl itemsControl)
    {
        EventHandler eventHandler = null;
        eventHandler =
            delegate
            {
                if (itemsControl.ItemContainerGenerator.Status == GeneratorStatus.ContainersGenerated)
                {
                    var scrollViewer = GetVisualChild<ScrollViewer>(itemsControl);
                    scrollViewer.ScrollToTop();
                    itemsControl.ItemContainerGenerator.StatusChanged -= eventHandler;
                }
            };
        itemsControl.ItemContainerGenerator.StatusChanged += eventHandler;
    }

    static T GetVisualChild<T>(DependencyObject parent) where T : Visual
    {
        T child = default(T);
        int numVisuals = VisualTreeHelper.GetChildrenCount(parent);
        for (var i = 0; i < numVisuals; i++)
        {
            var v = (Visual) VisualTreeHelper.GetChild(parent, i);
            child = v as T ?? GetVisualChild<T>(v);
            if (child != null)
            {
                break;
            }
        }
        return child;
    }

    #endregion
}

Answer 5

设置控件格式时，选择一系列单元格作为选择选项，然后将其列在列表框中。您还可以选择一个单元格作为指向所选选项的链接，其中将根据列表中选项的位置显示数字。 1 代表列表中的第一个，2 代表第二个，等等。代码非常简单：-

Range("A1")Select

Selection = 1

Change ("A1") 到您链接的单元格
并将 1 更改为您要选择的列表中的位置。

作为链接的单元格引用是双向的 - 如果您更改选择，单元格中的数字会更改；如果您更改单元格中的数字，突出显示的选择也会更改。