c# - 列表框滚动条不跟随所选项目(使用 ICollectionView)

Question

我正在尝试在 WPF 中实现 MVVM 模式。我关注了 Jeremy Alles 的 Very simple MVVM demo application 。我有一个 ListBox，它绑定(bind)到 ObservableCollection:

<ListBox
    Name="myListBox"
    IsSynchronizedWithCurrentItem="True"
    ItemsSource="{Binding Persons}">
    <ListBox.ItemTemplate>
        <DataTemplate>
            <views:PersonsView />
        </DataTemplate>
    </ListBox.ItemTemplate>
</ListBox>

我添加了一个ICollectionView来管理ListBox上的所选项目。它还允许我有两个按钮，允许我选择列表中的上一个和下一个项目。

private void GoToPrevious()
{
    this.collectionView.MoveCurrentToPrevious();
}
private void GoToNext()
{
    this.collectionView.MoveCurrentToNext();
}

一切都很好，但是，当所选项目位于列表框显示区域下方时，列表框的滚动条不会相应移动。

如何使列表框的滚动条/显示区域与所选项目同步？

Answer 1

我找到了答案。我需要使用

myListBoxItem.BringIntoView();

问题是我不想添加任何代码隐藏，因为我正在实现 MVVM。

解决方案是使用附加行为。乔什·史密斯(Josh Smith)有一篇关于此的精彩文章:Introduction to Attached Behaviors in WPF .

我为 ListBox 中的项目的样式添加了 Setter:

<ListBox.ItemContainerStyle>
    <Style TargetType="{x:Type ListBoxItem}">
        <Setter
            Property="custom:ListBoxItemBehavior.IsBroughtIntoViewWhenSelected"
            Value="True" />
    </Style>
</ListBox.ItemContainerStyle>

并添加了以下类(仅将 Josh 的文章中的 TreeView 更改为 ListBox):

public static class ListBoxItemBehavior
{
    #region IsBroughtIntoViewWhenSelected

    public static bool GetIsBroughtIntoViewWhenSelected(ListBoxItem listBoxItem)
    {
        return (bool)listBoxItem.GetValue(IsBroughtIntoViewWhenSelectedProperty);
    }

    public static void SetIsBroughtIntoViewWhenSelected(
      ListBoxItem listBoxItem, bool value)
    {
        listBoxItem.SetValue(IsBroughtIntoViewWhenSelectedProperty, value);
    }

    public static readonly DependencyProperty IsBroughtIntoViewWhenSelectedProperty =
        DependencyProperty.RegisterAttached(
        "IsBroughtIntoViewWhenSelected",
        typeof(bool),
        typeof(ListBoxItemBehavior),
        new UIPropertyMetadata(false, OnIsBroughtIntoViewWhenSelectedChanged));

    static void OnIsBroughtIntoViewWhenSelectedChanged(
      DependencyObject depObj, DependencyPropertyChangedEventArgs e)
    {
        ListBoxItem item = depObj as ListBoxItem;
        if (item == null)
            return;

        if (e.NewValue is bool == false)
            return;

        if ((bool)e.NewValue)
            item.Selected += OnListBoxItemSelected;
        else
            item.Selected -= OnListBoxItemSelected;
    }

    static void OnListBoxItemSelected(object sender, RoutedEventArgs e)
    {
        // Only react to the Selected event raised by the ListBoxItem
        // whose IsSelected property was modified.  Ignore all ancestors
        // who are merely reporting that a descendant's Selected fired.
        if (!Object.ReferenceEquals(sender, e.OriginalSource))
            return;

        ListBoxItem item = e.OriginalSource as ListBoxItem;
        if (item != null)
            item.BringIntoView();
    }

    #endregion // IsBroughtIntoViewWhenSelected
}

它有效!!