问题
A question about dragging and dropping tree view items in WPF.
My original question is a little complex. So I simplified it, and here is the code: XAML
<Window x:Class="WpfApplication2.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Window1" Height="300" Width="300">
<Grid>
<TreeView>
<TreeView.ItemContainerStyle>
<Style>
<Setter Property="TreeViewItem.IsExpanded" Value="True"/>
<Setter Property="TreeViewItem.Background" Value="LightBlue"/>
<Setter Property="TreeViewItem.AllowDrop" Value="True"/>
<EventSetter Event="TreeViewItem.MouseMove" Handler="TreeNode_MouseMove"/>
<EventSetter Event="TreeViewItem.Drop" Handler="TreeNode_Drop"/>
</Style>
</TreeView.ItemContainerStyle>
<TreeViewItem Header="first node in the tree"/>
<TreeViewItem Header="second node in the tree"></TreeViewItem>
<TreeViewItem Header="third node in the tree"></TreeViewItem>
</TreeView>
</Grid>
And code-behind:
public partial class Window1 : Window
{
public Window1()
{
InitializeComponent();
}
private void TreeNode_MouseMove(object sender, MouseEventArgs e)
{
if (e.LeftButton == MouseButtonState.Pressed)
{
DragDrop.DoDragDrop(this, DateTime.Now.ToString(), DragDropEffects.Move);
}
}
private void TreeNode_Drop(object sender, DragEventArgs e)
{
string str = (string)e.Data.GetData(typeof(string));
MessageBox.Show(str);
}
}
So what I want to do is very simple, just pop up a message box when one tree view item is dragged and dropped on another tree view item.
When I drop it right on another item, it works fine, like this:
But if I drag it slightly off the boundary of the item, it does not work, like this:
The mouse cursor is displayed as a “forbidden sign”, sorry I can’t get it in the screen shot.
So now my question is: how to make the second condition work? How to make the Drop event still fire up when the dropping location is slightly off the boundary of the item?
Thanks in advance.
回答1:
Take the default ControlTemplate of TreeViewItem and make the Border (the border which contains the ContentPresenter) to have a colspan of 2, e.g.:
<Border
BorderThickness="{TemplateBinding Border.BorderThickness}"
Padding="{TemplateBinding Control.Padding}"
BorderBrush="{TemplateBinding Border.BorderBrush}"
Background="{TemplateBinding Panel.Background}"
Name="Bd"
SnapsToDevicePixels="True"
Grid.Column="1" Grid.ColumnSpan="2">
Note that the whole area in TreeViewItem next to the TextBlock would become clickable. You may want to play around with the template to fit it to your needs.
Below is the ControlTemplate of TreeViewItem extracted using Dump Control Template Utility.
<?xml version="1.0" encoding="utf-16"?>
<ControlTemplate
TargetType="TreeViewItem" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:s="clr-namespace:System;assembly=mscorlib" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition
Width="Auto"
MinWidth="19" />
<ColumnDefinition
Width="Auto" />
<ColumnDefinition
Width="*" />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition
Height="Auto" />
<RowDefinition />
</Grid.RowDefinitions>
<ToggleButton
IsChecked="False"
ClickMode="Press"
Name="Expander">
<ToggleButton.Style>
<Style
TargetType="ToggleButton">
<Style.Resources>
<ResourceDictionary />
</Style.Resources>
<Setter
Property="UIElement.Focusable">
<Setter.Value>
<s:Boolean>False</s:Boolean>
</Setter.Value>
</Setter>
<Setter
Property="FrameworkElement.Width">
<Setter.Value>
<s:Double>19</s:Double>
</Setter.Value>
</Setter>
<Setter
Property="FrameworkElement.Height">
<Setter.Value>
<s:Double>13</s:Double>
</Setter.Value>
</Setter>
<Setter
Property="Control.Template">
<Setter.Value>
<ControlTemplate
TargetType="ToggleButton">
<Border
Background="#00FFFFFF"
Width="19"
Height="13">
<Border
BorderThickness="1,1,1,1"
CornerRadius="1,1,1,1"
BorderBrush="#FF7898B5"
Width="9"
Height="9"
SnapsToDevicePixels="True">
<Border.Background>
<LinearGradientBrush
StartPoint="0,0"
EndPoint="1,1">
<LinearGradientBrush.GradientStops>
<GradientStop
Color="#FFFFFFFF"
Offset="0.2" />
<GradientStop
Color="#FFC0B7A6"
Offset="1" />
</LinearGradientBrush.GradientStops>
</LinearGradientBrush>
</Border.Background>
<Path
Data="M0,2L0,3 2,3 2,5 3,5 3,3 5,3 5,2 3,2 3,0 2,0 2,2z"
Fill="#FF000000"
Name="ExpandPath"
Margin="1,1,1,1" />
</Border>
</Border>
<ControlTemplate.Triggers>
<Trigger
Property="ToggleButton.IsChecked">
<Setter
Property="Path.Data"
TargetName="ExpandPath">
<Setter.Value>
<StreamGeometry>M0,2L0,3 5,3 5,2z</StreamGeometry>
</Setter.Value>
</Setter>
<Trigger.Value>
<s:Boolean>True</s:Boolean>
</Trigger.Value>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</ToggleButton.Style>
</ToggleButton>
<Border
BorderThickness="{TemplateBinding Border.BorderThickness}"
Padding="{TemplateBinding Control.Padding}"
BorderBrush="{TemplateBinding Border.BorderBrush}"
Background="{TemplateBinding Panel.Background}"
Name="Bd"
SnapsToDevicePixels="True"
Grid.Column="1">
<ContentPresenter
Content="{TemplateBinding HeaderedContentControl.Header}"
ContentTemplate="{TemplateBinding HeaderedContentControl.HeaderTemplate}"
ContentStringFormat="{TemplateBinding HeaderedItemsControl.HeaderStringFormat}"
ContentSource="Header"
Name="PART_Header"
HorizontalAlignment="{TemplateBinding Control.HorizontalContentAlignment}"
SnapsToDevicePixels="{TemplateBinding UIElement.SnapsToDevicePixels}" />
</Border>
<ItemsPresenter
Name="ItemsHost"
Grid.Column="1"
Grid.Row="1"
Grid.ColumnSpan="2" />
</Grid>
<ControlTemplate.Triggers>
<Trigger
Property="TreeViewItem.IsExpanded">
<Setter
Property="UIElement.Visibility"
TargetName="ItemsHost">
<Setter.Value>
<x:Static
Member="Visibility.Collapsed" />
</Setter.Value>
</Setter>
<Trigger.Value>
<s:Boolean>False</s:Boolean>
</Trigger.Value>
</Trigger>
<Trigger
Property="ItemsControl.HasItems">
<Setter
Property="UIElement.Visibility"
TargetName="Expander">
<Setter.Value>
<x:Static
Member="Visibility.Hidden" />
</Setter.Value>
</Setter>
<Trigger.Value>
<s:Boolean>False</s:Boolean>
</Trigger.Value>
</Trigger>
<Trigger
Property="TreeViewItem.IsSelected">
<Setter
Property="Panel.Background"
TargetName="Bd">
<Setter.Value>
<DynamicResource
ResourceKey="{x:Static SystemColors.HighlightBrushKey}" />
</Setter.Value>
</Setter>
<Setter
Property="TextElement.Foreground">
<Setter.Value>
<DynamicResource
ResourceKey="{x:Static SystemColors.HighlightTextBrushKey}" />
</Setter.Value>
</Setter>
<Trigger.Value>
<s:Boolean>True</s:Boolean>
</Trigger.Value>
</Trigger>
<MultiTrigger>
<MultiTrigger.Conditions>
<Condition
Property="TreeViewItem.IsSelected">
<Condition.Value>
<s:Boolean>True</s:Boolean>
</Condition.Value>
</Condition>
<Condition
Property="Selector.IsSelectionActive">
<Condition.Value>
<s:Boolean>False</s:Boolean>
</Condition.Value>
</Condition>
</MultiTrigger.Conditions>
<Setter
Property="Panel.Background"
TargetName="Bd">
<Setter.Value>
<DynamicResource
ResourceKey="{x:Static SystemColors.ControlBrushKey}" />
</Setter.Value>
</Setter>
<Setter
Property="TextElement.Foreground">
<Setter.Value>
<DynamicResource
ResourceKey="{x:Static SystemColors.ControlTextBrushKey}" />
</Setter.Value>
</Setter>
</MultiTrigger>
<Trigger
Property="UIElement.IsEnabled">
<Setter
Property="TextElement.Foreground">
<Setter.Value>
<DynamicResource
ResourceKey="{x:Static SystemColors.GrayTextBrushKey}" />
</Setter.Value>
</Setter>
<Trigger.Value>
<s:Boolean>False</s:Boolean>
</Trigger.Value>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
回答2:
use AllowDrop property and Drop event for TreeView itself.
this is from msdn: http://social.msdn.microsoft.com/Forums/en-US/wpf/thread/4b8bafe5-ae3e-439d-953a-f534a60dbb2d/
来源：https://stackoverflow.com/questions/5740655/dragging-and-dropping-treeviewitems-in-non-clickable-area-of-treeview-wpf