.net - 突出显示被拖动的 TreeView 项目

Question

在我的应用程序中，我有一个允许拖放的 TreeView。我的所有功能都可以正常工作，但是当拖拽 TreeViewItem 时我很难突出显示它。这是我的树视图项目的风格。IsMouseOver 触发器在拖动时不起作用，因为拖动似乎会阻止其他鼠标事件。任何人都可以帮我在拖动时触发我的树视图项目上的相同边框更改吗？

<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>

score 19 · Accepted Answer

我为此使用了一个附加属性，然后在我的 xaml 文件中使用该属性来更改树视图项的背景颜色：

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
    }
}

然后在 xaml 文件中：

    <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>

score 4 · Accepted Answer

4

查看DragOver事件（可能还有 DragEnter/DragLeave）而不是 IsMouseOver。

于 2009-03-12T18:29:23.800 回答

score 2 · Accepted Answer

除了 Stefan 的回答，我发现还需要添加 Drop 事件：

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);
        }
    }
}

并注册 drop 事件：

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

否则，如果一个 treeItem 掉落在另一个之上，则背景可能不会改变。如果你按 ESC 也是一样。

score 1 · Accepted Answer

对于我们这些在这些范围内工作的人来说，这篇文章只是将 Stefan 上面对 VB 的精彩回应的移植；除了希望我没有把任何事情搞砸之外，我没有什么可提供的。它似乎对我有用：

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

结束命名空间

.net - 突出显示被拖动的 TreeView 项目

4 回答 4

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