Tô sáng mục TreeView đang được kéo trên

Question

Trong ứng dụng của tôi, tôi có TreeView cho phép kéo/thả. Tôi có tất cả các chức năng làm việc tốt, tuy nhiên tôi gặp khó khăn làm nổi bật một TreeViewItem khi nó được kéo qua. Đây là phong cách của tôi cho mục treeview của tôi. Trình kích hoạt IsMouseOver không hoạt động khi đang kéo, vì việc kéo dường như chặn các sự kiện chuột khác. Bất cứ ai có thể giúp tôi kích hoạt các thay đổi biên giới tương tự trên mục treeview của tôi trong khi kéo?

<Style x:Key="TreeViewItemStyle" TargetType="{x:Type TreeViewItem}"> 
    <Setter Property="Template"> 
     <Setter.Value> 
      <ControlTemplate TargetType="{x:Type TreeViewItem}"> 
       <Grid> 
        <Grid.ColumnDefinitions> 
         <ColumnDefinition MinWidth="19" Width="Auto"/> 
         <ColumnDefinition Width="Auto"/> 
         <ColumnDefinition Width="*"/> 
        </Grid.ColumnDefinitions> 
        <Grid.RowDefinitions> 
         <RowDefinition Height="Auto"/> 
         <RowDefinition/> 
        </Grid.RowDefinitions> 
        <ToggleButton 
         x:Name="PART_Expander" 
         Style="{StaticResource ExpandCollapseToggleStyle}" 
         IsChecked="{Binding Path=IsExpanded, RelativeSource={RelativeSource TemplatedParent}}" 
         ClickMode="Press" 
         /> 
        <Border 
         x:Name="OuterBorder" 
         Grid.Column="1" 
         SnapsToDevicePixels="True" 
         BorderThickness="1" 
         CornerRadius="3" 
         BorderBrush="Transparent" 
         Background="Transparent" 
         > 
         <Border 
          x:Name="InnerBorder" 
          SnapsToDevicePixels="True" 
          BorderThickness="1" 
          CornerRadius="2" 
          BorderBrush="Transparent" 
          Background="Transparent" 
          > 
          <ContentPresenter 
           x:Name="PART_Content" 
           ContentSource="Header" 
           HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" 
           /> 
         </Border> 
        </Border> 
        <ItemsPresenter 
         x:Name="PART_ItemsHost" 
         Grid.Row="1" 
         Grid.Column="1" 
         Grid.ColumnSpan="2" 
         /> 
       </Grid> 
       <ControlTemplate.Triggers> 
        <Trigger Property="IsMouseOver" SourceName="OuterBorder" Value="True"> 
         <Setter TargetName="OuterBorder" Property="BorderBrush" Value="Blue" /> 
         <Setter TargetName="OuterBorder" Property="Background" Value="Red" /> 
         <Setter TargetName="InnerBorder" Property="BorderBrush" Value="White" /> 
        </Trigger> 
        <MultiTrigger> 
       </ControlTemplate.Triggers> 
      </ControlTemplate> 
     </Setter.Value> 
    </Setter> 
</Style> 

Answer 1

Tôi đang sử dụng một tài sản gắn liền cho điều này, và sau đó sử dụng tài sản đó trong file XAML của tôi để thay đổi màu nền của mặt hàng đó xem dạng cây:

using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Text; 
using System.Windows; 
using System.Windows.Controls; 
using System.Windows.Input; 

namespace SKNotes.Utilities 
{ 
    /// <summary> 
    /// Implements an attached property used for styling TreeViewItems when 
    /// they're a possible drop target. 
    /// </summary> 
    public static class TreeViewDropHighlighter 
    { 
     #region private variables 
     /// <summary> 
     /// the TreeViewItem that is the current drop target 
     /// </summary> 
     private static TreeViewItem _currentItem = null; 

     /// <summary> 
     /// Indicates whether the current TreeViewItem is a possible 
     /// drop target 
     /// </summary> 
     private static bool _dropPossible; 
     #endregion 

     #region IsPossibleDropTarget 
     /// <summary> 
     /// Property key (since this is a read-only DP) for the IsPossibleDropTarget property. 
     /// </summary> 
     private static readonly DependencyPropertyKey IsPossibleDropTargetKey = 
            DependencyProperty.RegisterAttachedReadOnly(
             "IsPossibleDropTarget", 
             typeof(bool), 
             typeof(TreeViewDropHighlighter), 
             new FrameworkPropertyMetadata(null, 
              new CoerceValueCallback(CalculateIsPossibleDropTarget))); 


     /// <summary> 
     /// Dependency Property IsPossibleDropTarget. 
     /// Is true if the TreeViewItem is a possible drop target (i.e., if it would receive 
     /// the OnDrop event if the mouse button is released right now). 
     /// </summary> 
     public static readonly DependencyProperty IsPossibleDropTargetProperty = IsPossibleDropTargetKey.DependencyProperty; 

     /// <summary> 
     /// Getter for IsPossibleDropTarget 
     /// </summary> 
     public static bool GetIsPossibleDropTarget(DependencyObject obj) 
     { 
      return (bool)obj.GetValue(IsPossibleDropTargetProperty); 
     } 

     /// <summary> 
     /// Coercion method which calculates the IsPossibleDropTarget property. 
     /// </summary> 
     private static object CalculateIsPossibleDropTarget(DependencyObject item, object value) 
     { 
      if ((item == _currentItem) && (_dropPossible)) 
       return true; 
      else 
       return false; 
     } 
     #endregion 

     /// <summary> 
     /// Initializes the <see cref="TreeViewDropHighlighter"/> class. 
     /// </summary> 
     static TreeViewDropHighlighter() 
     { 
      // Get all drag enter/leave events for TreeViewItem. 
      EventManager.RegisterClassHandler(typeof(TreeViewItem), 
             TreeViewItem.PreviewDragEnterEvent, 
             new DragEventHandler(OnDragEvent), true); 
      EventManager.RegisterClassHandler(typeof(TreeViewItem), 
             TreeViewItem.PreviewDragLeaveEvent, 
             new DragEventHandler(OnDragLeave), true); 
      EventManager.RegisterClassHandler(typeof(TreeViewItem), 
             TreeViewItem.PreviewDragOverEvent, 
             new DragEventHandler(OnDragEvent), true); 
     } 

     #region event handlers 
     /// <summary> 
     /// Called when an item is dragged over the TreeViewItem. 
     /// </summary> 
     /// <param name="sender">The sender.</param> 
     /// <param name="args">The <see cref="System.Windows.DragEventArgs"/> instance containing the event data.</param> 
     static void OnDragEvent(object sender, DragEventArgs args) 
     { 
      lock (IsPossibleDropTargetProperty) 
      { 
       _dropPossible = false; 

       if (_currentItem != null) 
       { 
        // Tell the item that previously had the mouse that it no longer does. 
        DependencyObject oldItem = _currentItem; 
        _currentItem = null; 
        oldItem.InvalidateProperty(IsPossibleDropTargetProperty); 
       } 

       if (args.Effects != DragDropEffects.None) 
       { 
        _dropPossible = true; 
       } 

       TreeViewItem tvi = sender as TreeViewItem; 
       if (tvi != null) 
       { 
        _currentItem = tvi; 
        // Tell that item to re-calculate the IsPossibleDropTarget property 
        _currentItem.InvalidateProperty(IsPossibleDropTargetProperty); 
       } 
      } 
     } 

     /// <summary> 
     /// Called when the drag cursor leaves the TreeViewItem 
     /// </summary> 
     /// <param name="sender">The sender.</param> 
     /// <param name="args">The <see cref="System.Windows.DragEventArgs"/> instance containing the event data.</param> 
     static void OnDragLeave(object sender, DragEventArgs args) 
     { 
      lock (IsPossibleDropTargetProperty) 
      { 
       _dropPossible = false; 

       if (_currentItem != null) 
       { 
        // Tell the item that previously had the mouse that it no longer does. 
        DependencyObject oldItem = _currentItem; 
        _currentItem = null; 
        oldItem.InvalidateProperty(IsPossibleDropTargetProperty); 
       } 

       TreeViewItem tvi = sender as TreeViewItem; 
       if (tvi != null) 
       { 
        _currentItem = tvi; 
        tvi.InvalidateProperty(IsPossibleDropTargetProperty); 
       } 
      } 
     } 
     #endregion 
    } 
} 

và sau đó trong file XAML:

<TreeView.ItemContainerStyle> 
     <Style TargetType="{x:Type TreeViewItem}"> 
      <Setter Property="FontWeight" Value="Normal" /> 
      <Style.Triggers> 
       <Trigger Property="utils:TreeViewDropHighlighter.IsPossibleDropTarget" Value="True"> 
        <Setter Property="Background" Value="{DynamicResource {x:Static SystemColors.HighlightBrushKey}}" /> 
       </Trigger> 
      </Style.Triggers> 
     </Style> 
    </TreeView.ItemContainerStyle> 

Answer 2

Nhìn vào sự kiện DragOver (và có thể DragEnter/DragLeave) thay vì IsMouseOver.

Answer 3

Bài đăng này chỉ đơn giản là việc chuyển giao phản hồi tuyệt vời của Stefan ở trên cho VB, cho những người trong chúng ta làm việc trong những giới hạn đó; Tôi không có gì để cung cấp ngoại trừ hy vọng tôi đã không vít bất cứ điều gì lên quá nặng. Nó xuất hiện để làm việc cho tôi:

Namespace SKNotes.Utilities 

''' <summary> 
''' Implements an attached property used for styling TreeViewItems when 
''' they are a possible drop target. 
''' </summary> 
Public Class TreeViewDropHighlighter 

    ''' <summary> 
    ''' The TreeViewItem that is the current drop target 
    ''' </summary> 
    Private Shared _CurrentItem As TreeViewItem = Nothing 

    ''' <summary> 
    ''' Indicates whether the current TreeView Item is a possible drop target 
    ''' </summary> 
    ''' <remarks></remarks> 
    Private Shared _DropPossible As Boolean 

    ''' <summary> 
    ''' Property Key (since this is a read only DP) for the IsPossibleDropTarget property. 
    ''' </summary> 
    ''' <remarks></remarks> 
    Private Shared ReadOnly IsPossibleDropTargetKey As DependencyPropertyKey = _ 
              DependencyProperty.RegisterAttachedReadOnly _ 
              (_ 
               "IsPossibleDropTarget", _ 
               GetType(Boolean), _ 
               GetType(TreeViewDropHighlighter), _ 
               New FrameworkPropertyMetadata(Nothing, _ 
                       New CoerceValueCallback(AddressOf CalculateIsPossibleDropTarget) 
                       ) 
              ) 
    ''' <summary> 
    ''' Dependency Property IsPossibleDropTarget. 
    ''' Is true if the TreeViewItem is a possible drop target (ie, if it would receive the 
    ''' OnDrop even if the mouse button is release right now). 
    ''' </summary> 
    ''' <remarks></remarks> 
    Public Shared ReadOnly IsPossibleDropTargetProperty As DependencyProperty = IsPossibleDropTargetKey.DependencyProperty 

    ''' <summary> 
    ''' Getter for IsPossibleDropTarget 
    ''' </summary> 
    Public Shared Function GetIsPossibleDropTarget(ByVal obj As DependencyObject) As Boolean 
     Return CBool(obj.GetValue(IsPossibleDropTargetProperty)) 
    End Function 

    ''' <summary> 
    ''' Coercion method which calculates the IsPossibleDropTarget property 
    ''' </summary> 
    Private Shared Function CalculateIsPossibleDropTarget(item As DependencyObject, value As Object) As Object 
     If item.Equals(_CurrentItem) And _ 
      _DropPossible Then 
      Return True 
     Else 
      Return False 
     End If 
    End Function 

    ''' <summary> 
    ''' Initializes the TreeViewDropHighlighter class 
    ''' </summary> 
    Shared Sub New() 
     EventManager.RegisterClassHandler(GetType(TreeViewItem), _ 
              TreeViewItem.PreviewDragEnterEvent, _ 
              New DragEventHandler(AddressOf OnDragEvent), True) 
     EventManager.RegisterClassHandler(GetType(TreeViewItem), _ 
              TreeViewItem.PreviewDragLeaveEvent, 
              New DragEventHandler(AddressOf OnDragLeave), True) 
     EventManager.RegisterClassHandler(GetType(TreeViewItem), _ 
              TreeViewItem.PreviewDragOverEvent, _ 
              New DragEventHandler(AddressOf OnDragEvent), True) 
    End Sub 

    ''' <summary> 
    ''' Called when an item is dragged over the TreeView Item 
    ''' </summary> 
    ''' <param name="sender">The sender</param> 
    ''' <param name="args">The System.Windows.DragEventArgs instance containing the event data</param> 
    ''' <remarks></remarks> 
    Shared Sub OnDragEvent(sender As Object, args As DragEventArgs) 
     SyncLock (IsPossibleDropTargetProperty) 
      _DropPossible = False 
      If Not IsNothing(_CurrentItem) Then 
       'Tell the item that previously had the mouse that it no longer does. 
       Dim OldItem As DependencyObject = _CurrentItem 
       _CurrentItem = Nothing 
       OldItem.InvalidateProperty(IsPossibleDropTargetProperty) 
      End If 

      If args.Effects <> DragDropEffects.None Then 
       _DropPossible = True 
      End If 

      Dim tvi As TreeViewItem = CType(sender, TreeViewItem) 
      If Not IsNothing(tvi) Then 
       _CurrentItem = tvi 
       'Tell that item to recalculate the IsPossibleDropTarget property 
       _CurrentItem.InvalidateProperty(IsPossibleDropTargetProperty) 
      End If 
     End SyncLock 
    End Sub 

    Shared Sub OnDragLeave(sender As Object, args As DragEventArgs) 

     SyncLock (IsPossibleDropTargetProperty) 
      _DropPossible = False 
      If Not IsNothing(_CurrentItem) Then 
       'Tell the item that previously had the mouse that it no longer does 
       Dim OldItem As DependencyObject = _CurrentItem 
       _CurrentItem = Nothing 
       OldItem.InvalidateProperty(IsPossibleDropTargetProperty) 
      End If 

      Dim tvi As TreeViewItem = CType(sender, TreeViewItem) 
      If Not IsNothing(tvi) Then 
       _CurrentItem = tvi 
       tvi.InvalidateProperty(IsPossibleDropTargetProperty) 
      End If 

     End SyncLock 

    End Sub 

End Class 

End Namespace

Answer 4

Ngoài câu trả lời Stefan, tôi thấy rằng là cần thiết để thêm cũng là sự kiện Drop:

static void OnDragDrop(object sender, DragEventArgs args) 
{ 
    lock (IsPossibleDropTargetProperty) 
    { 
     _dropPossible = false; 

     if (_currentItem != null) 
     { 
      _currentItem.InvalidateProperty(IsPossibleDropTargetProperty); 
     } 

     TreeViewItem tvi = sender as TreeViewItem; 
     if (tvi != null) 
     { 
      tvi.InvalidateProperty(IsPossibleDropTargetProperty); 
     } 
    } 
} 

và đăng ký thả sự kiện cũng :

EventManager.RegisterClassHandler(typeof(TreeViewItem), 
      TreeViewItem.PreviewDropEvent, 
      new DragEventHandler(OnDragDrop), true); 

Nếu không xảy ra sự sụt giảm của một câyNó khác, nền có thể không thay đổi. Điều tương tự nếu bạn nhấn ESC.