wpf - 如何使用 caliburn.micro 从 View 模型设置滚动位置？

Question

我有一个 ListBox在我看来，绑定(bind)到一个动态增长的集合。我希望滚动位置跟随最后添加的项目(附加到列表底部)。如何使用 Caliburn.Micro 实现这一目标？

Answer 1

另一种方法是使用事件聚合器将消息发布到 View 。

就像是:

Aggregator.Publish(ItemAddedMessage<SomeItemType>(itemThatWasJustAdded));

在 View 中:

public class SomeView : IHandle<ItemAddedMessage<SomeItemType>>
{

   public void Handle(ItemAddedMessage<SomeItemType> message)
   {
       // Implement view specific behaviour here
   }
}

这取决于您的要求，但至少 View 负责显示问题，您仍然可以测试 VM

您也可以只在 View 中实现代码 - 因为它似乎是一个 View 问题(例如，使用列表框提供的事件)

一种行为也会很有用，但可能与您的类型的耦合度较低 - 例如通用行为 SeekAddedItemBehaviour它 Hook 列表框事件以查找最后一项。不确定列表框是否公开了所需的事件，但值得一看

编辑:

好的，这可能会完全停止 - 你应该能够将此行为附加到列表框，它应该负责其余的:

public class ListBoxSeekLastItemBehaviour : System.Windows.Interactivity.Behavior<ListBox>
{
    private static readonly DependencyProperty ItemsSourceWatcherProperty = DependencyProperty.Register("ItemsSourceWatcher", typeof(object), typeof(ListBoxSeekLastItemBehaviour), new PropertyMetadata(null, OnItemsSourceWatcherPropertyChanged));

    private ListBox _listBox = null;

    private static void OnItemsSourceWatcherPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        ListBoxSeekLastItemBehaviour source = d as ListBoxSeekLastItemBehaviour;

        if (source != null)
            source.OnItemsSourceWatcherPropertyChanged();
    }

    private void OnItemsSourceWatcherPropertyChanged()
    {
        // The itemssource has changed, check if it raises collection changed notifications
        if (_listBox.ItemsSource is INotifyCollectionChanged)
        {
            // if it does, hook the CollectionChanged event so we can respond to items being added
            (_listBox.ItemsSource as INotifyCollectionChanged).CollectionChanged += new NotifyCollectionChangedEventHandler(ListBoxSeekLastItemBehaviour_CollectionChanged);
        }
    }

    void ListBoxSeekLastItemBehaviour_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        if (e.Action == NotifyCollectionChangedAction.Add && e.NewItems.Count > 0)
        {
            // If an item was added seek it
            ScrollIntoView(e.NewItems[0]);
        }
    }

    protected override void OnAttached()
    {
        base.OnAttached();

        // We've been attached - get the associated listbox
        var box = this.AssociatedObject as ListBox;

        if (box != null)
        {
            // Hold a ref
            _listBox = box;

            // Set a binding to watch for property changes
            System.Windows.Data.Binding binding = new System.Windows.Data.Binding("ItemsSource") { Source = _listBox; }  

            // EDIT: Potential bugfix - you probably want to check the itemssource here just 
            // in case the behaviour is applied after the original ItemsSource binding has been evaluated - otherwise you might miss the change
            OnItemsSourceWatcherPropertyChanged();
        }
    }

    private void ScrollIntoView(object target)
    {
        // Set selected item and try and scroll it into view
        _listBox.SelectedItem = target;
        _listBox.ScrollIntoView(target);
    }
}

您可能想稍微整理一下，并确保 CollectionChanged 的事件处理程序当 ItemsSource 被删除变化。

你也可以叫它 SeekLastAddedItemBehaviour或 SeekLastAddedItemBehavior - 我倾向于保留美式拼写，因为它与 Microsoft 的拼写匹配。我认为 SeekLastItem听起来它会滚动到列表中的最后一项而不是最后添加的项目