五年在编程方面是很长的时间......
在获得 2500 次观看的徽章后，我最近回到了这个问题。碰巧我不久前在我的博客上发表了一篇关于这些问题的解决方案的帖子 - http://peregrinesview.uk/wpf-behaviors-part-2-treeview/。
我知道在 stackoverflow 上通常不会批准仅链接的答案，所以我也会在这里发布关键元素。
1) TreeViewItem 的助手包含两个附加属性，一个用于将所选项目滚动到视图中，另一个用于在项目展开时将尽可能多的子项滚动到视图中。
public static class perTreeViewItemHelper
{
public static bool GetBringSelectedItemIntoView(TreeViewItem treeViewItem)
{
return (bool)treeViewItem.GetValue(BringSelectedItemIntoViewProperty);
}
public static void SetBringSelectedItemIntoView(TreeViewItem treeViewItem, bool value)
{
treeViewItem.SetValue(BringSelectedItemIntoViewProperty, value);
}
public static readonly DependencyProperty BringSelectedItemIntoViewProperty =
DependencyProperty.RegisterAttached(
"BringSelectedItemIntoView",
typeof(bool),
typeof(perTreeViewItemHelper),
new UIPropertyMetadata(false, BringSelectedItemIntoViewChanged));
private static void BringSelectedItemIntoViewChanged(DependencyObject obj, DependencyPropertyChangedEventArgs args)
{
if (!(args.NewValue is bool))
return;
var item = obj as TreeViewItem;
if (item == null)
return;
if ((bool)args.NewValue)
item.Selected += OnTreeViewItemSelected;
else
item.Selected -= OnTreeViewItemSelected;
}
private static void OnTreeViewItemSelected(object sender, RoutedEventArgs e)
{
var item = e.OriginalSource as TreeViewItem;
item?.BringIntoView();
// prevent this event bubbling up to any parent nodes
e.Handled = true;
}
public static bool GetBringExpandedChildrenIntoView(TreeViewItem treeViewItem)
{
return (bool)treeViewItem.GetValue(BringExpandedChildrenIntoViewProperty);
}
public static void SetBringExpandedChildrenIntoView(TreeViewItem treeViewItem, bool value)
{
treeViewItem.SetValue(BringExpandedChildrenIntoViewProperty, value);
}
public static readonly DependencyProperty BringExpandedChildrenIntoViewProperty =
DependencyProperty.RegisterAttached(
"BringExpandedChildrenIntoView",
typeof(bool),
typeof(perTreeViewItemHelper),
new UIPropertyMetadata(false, BringExpandedChildrenIntoViewChanged));
private static void BringExpandedChildrenIntoViewChanged(DependencyObject obj, DependencyPropertyChangedEventArgs args)
{
if (!(args.NewValue is bool))
return;
var item = obj as TreeViewItem;
if (item == null)
return;
if ((bool)args.NewValue)
item.Expanded += OnTreeViewItemExpanded;
else
item.Expanded -= OnTreeViewItemExpanded;
}
private static void OnTreeViewItemExpanded(object sender, RoutedEventArgs e)
{
var item = e.OriginalSource as TreeViewItem;
if (item == null)
return;
// use DispatcherPriority.ContextIdle, so that we wait for all of the UI elements for any newly visible children to be created
// first bring the last child into view
Action action = () =>
{
var lastChild = item.ItemContainerGenerator.ContainerFromIndex(item.Items.Count - 1) as TreeViewItem;
lastChild?.BringIntoView();
};
item.Dispatcher.BeginInvoke(action, DispatcherPriority.ContextIdle);
// then bring the expanded item (back) into view
action = () => { item.BringIntoView(); };
item.Dispatcher.BeginInvoke(action, DispatcherPriority.ContextIdle);
// prevent this event bubbling up to any parent nodes
e.Handled = true;
}
}
2) TreeViewItem 的样式包括这些属性
<Style x:Key="perExpandCollapseToggleStyle"
TargetType="ToggleButton">
<Setter Property="Focusable" Value="False" />
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="ToggleButton">
<Grid Width="10"
Height="10"
Background="Transparent">
<Path x:Name="ExpanderGlyph"
Margin="1"
HorizontalAlignment="Left"
VerticalAlignment="Center"
Data="M 0,3 L 0,5 L 3,5 L 3,8 L 5,8 L 5,5 L 8,5 L 8,3 L 5,3 L 5,0 L 3,0 L 3,3 z"
Fill="LightGreen"
Stretch="None" />
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="IsChecked" Value="True">
<Setter TargetName="ExpanderGlyph" Property="Data" Value="M 0,0 M 8,8 M 0,3 L 0,5 L 8,5 L 8,3 z" />
<Setter TargetName="ExpanderGlyph" Property="Fill" Value="Red" />
</Trigger>
<Trigger Property="IsEnabled" Value="False">
<Setter TargetName="ExpanderGlyph" Property="Fill" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}" />
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<Style x:Key="perTreeViewItemContainerStyle"
TargetType="{x:Type TreeViewItem}">
<!-- Link the properties of perTreeViewItemViewModelBase to the corresponding ones on the TreeViewItem -->
<Setter Property="IsExpanded" Value="{Binding IsExpanded, Mode=TwoWay}" />
<Setter Property="IsSelected" Value="{Binding IsSelected, Mode=TwoWay}" />
<Setter Property="IsEnabled" Value="{Binding IsEnabled}" />
<!-- Include the two "Scroll into View" behaviors -->
<Setter Property="vhelp:perTreeViewItemHelper.BringSelectedItemIntoView" Value="True" />
<Setter Property="vhelp:perTreeViewItemHelper.BringExpandedChildrenIntoView" Value="True" />
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type TreeViewItem}">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"
MinWidth="14" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<ToggleButton x:Name="Expander"
Grid.Row="0"
Grid.Column="0"
ClickMode="Press"
IsChecked="{Binding Path=IsExpanded, RelativeSource={RelativeSource TemplatedParent}}"
Style="{StaticResource perExpandCollapseToggleStyle}" />
<Border x:Name="PART_Border"
Grid.Row="0"
Grid.Column="1"
Padding="{TemplateBinding Padding}"
Background="{TemplateBinding Background}"
BorderBrush="{TemplateBinding BorderBrush}"
BorderThickness="{TemplateBinding BorderThickness}">
<ContentPresenter x:Name="PART_Header"
Margin="0,2"
HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
ContentSource="Header" />
</Border>
<ItemsPresenter x:Name="ItemsHost"
Grid.Row="1"
Grid.Column="1" />
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="IsExpanded" Value="false">
<Setter TargetName="ItemsHost" Property="Visibility" Value="Collapsed" />
</Trigger>
<Trigger Property="HasItems" Value="false">
<Setter TargetName="Expander" Property="Visibility" Value="Hidden" />
</Trigger>
<!-- Use the same colors for a selected item, whether the TreeView is focussed or not -->
<Trigger Property="IsSelected" Value="true">
<Setter TargetName="PART_Border" Property="Background" Value="{DynamicResource {x:Static SystemColors.HighlightBrushKey}}" />
<Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.HighlightTextBrushKey}}" />
</Trigger>
<Trigger Property="IsEnabled" Value="false">
<Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}" />
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<Style TargetType="{x:Type TreeView}">
<Setter Property="ItemContainerStyle" Value="{StaticResource perTreeViewItemContainerStyle}" />
</Style>