当 PreviewMouseLeftButtonDownCommand RelayCommand\EventToCommand 触发时查找 ItemsControl 中的选定项目

Question

我的应用程序是 wpf mvvm，使用 RelayCommand\EventToCommand 绑定事件。我的应用程序执行一些典型的拖放操作从 ListBox 拖放到 ItemsControl 上（它实际上是一个图像控件，顶部有一个 ItemsControl，用于保存拖放的项目）。 ListBox 中填充有 vm ObservableCollection。 ItemsControl 也是一个 ObservableCollection，我将放置的 MyObj 项目插入其中。

当我从 ListBox 中拖动项目并将其放入 ItemsControl\image 时，一切正常。在 PreviewMouseLeftButtonDownCommand 中，我使用 System.Windows.Media.VisualTreeHelper 递归地向上遍历可视化树，因此当我从 ListBox 中拖动时，我可以找到正在拖动的 MyObj 项。但是，当我尝试从 ItemsControl 中拖动项目时，代码不起作用。我所能得到的只是项目（标签）的 DataTemplate 转换。所以我的问题是；当 PreviewMouseLeftButtonDownCommand RelayCommand\EventToCommand 触发时，如何从 ItemsControl 获取所选项目？

虚拟机 C#：

PreviewMouseLeftButtonDownCommand = new RelayCommand<MouseButtonEventArgs>(e =>
{
    if (e.Source is ListBox)
    {
    // get dragged list box item
    ListBox listBox = e.Source as ListBox;
    ListBoxItem listBoxItem = VisualHelper.FindAncestor<ListBoxItem>((DependencyObject)e.OriginalSource);

    // Find the data behind the listBoxItem
    if (listBox == null || listBoxItem == null) return;

    MyObj tag = (MyObj)listBox.ItemContainerGenerator.ItemFromContainer(listBoxItem);

     // Initialize the drag & drop operation
    DataObject dragData = new DataObject("myObj", tag);
    DragDrop.DoDragDrop(listBoxItem, dragData, DragDropEffects.Move);
}
else if (e.Source is ItemsControl)
{
    ItemsControl itemsControl = e.Source as ItemsControl;
    object item = VisualHelper.FindAncestor<UIElement>((DependencyObject)e.OriginalSource);

    if (itemsControl == null || item == null) return;

    MyObj tag = (MyObj)itemsControl.ItemContainerGenerator.ItemFromContainer(item);


    // Initialize the drag & drop operation
    DataObject dragData = new DataObject("myObj", tagDragging);
    DragDrop.DoDragDrop(item, dragData, DragDropEffects.Move);
    }
});

Answer 1

这是我过去使用过的代码：

private void DragSource_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
    // Get ItemsControl for object being dragged
    if (sender is ItemsControl)
        _sourceItemsControl = sender as ItemsControl;
    else if (sender is Panel)
        _sourceItemsControl = WPFHelpers.FindAncester<ItemsControl>(sender as Panel);

    // Get ItemContainer for object being dragged
    FrameworkElement sourceItemsContainer = _sourceItemsControl
        .ContainerFromElement((Visual)e.OriginalSource) as FrameworkElement;

    // Get data object for object being dragged
    if (sourceItemsContainer == null)
        _draggedObject = _sourceItemsControl.DataContext;
    else if (sourceItemsContainer == e.Source)
        _draggedObject = e.Source;
    else
        _draggedObject = sourceItemsContainer.DataContext;

}

WPF Helper 类

public class WPFHelpers
{
    public static T FindAncester<T>(DependencyObject current)
    where T : DependencyObject
    {
        current = VisualTreeHelper.GetParent(current);

        while (current != null)
        {
            if (current is T)
            {
                return (T)current;
            }
            current = VisualTreeHelper.GetParent(current);
        };
        return null;
    }
}