从 DataTrigger 在 WPF TreeViewItem 上设置 IsExpanded

Question

我正在尝试使用条件模板在XAML 中设置我的TreeView 项目的IsExpanded 属性：

<DataTrigger Binding="{Binding MyStatus}" Value="Opened">
    <Setter TargetName="MyTextBlock" Property="Foreground" Value="Green"/>
    <Setter Property="TreeViewItem.IsExpanded" Value="True" />
</DataTrigger>

当我从 C# 代码中设置 MyStatus 属性时，颜色会发生变化（因此 DataTrigger 可以工作），但节点没有展开。

_myItems[0].MyStatus = MyStatus.Opened;

如何从DataTrigger 设置TreeViewItem.IsExpanded 属性？

当我启动应用程序时，颜色设置正确，但绿色节点没有展开：

并且在更改_myItems[0].MyStatus和_myItems[1].MyStatus的值后，颜色也随之改变，但绿色节点仍未展开。

完整代码 (XAML)

完整的代码有点长，但它是 90% 的样板。

<Window x:Class="WpfApplication6.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="150" Width="250">
    <DockPanel>
        <DockPanel.Resources>
            <HierarchicalDataTemplate ItemsSource="{Binding SubItems}" x:Key="MyTemplate">
                <StackPanel Orientation="Horizontal">
                    <!-- ... -->
                    <TextBlock x:Name="MyTextBlock" Foreground="Green" Text="{Binding Name}" />
                </StackPanel>

                <HierarchicalDataTemplate.Triggers>
                    <DataTrigger Binding="{Binding MyStatus}" Value="Closed">
                        <Setter TargetName="MyTextBlock" Property="Foreground" Value="Red"/>
                        <Setter Property="TreeViewItem.IsExpanded" Value="False" />
                    </DataTrigger>
                    <DataTrigger Binding="{Binding MyStatus}" Value="Opened">
                        <Setter TargetName="MyTextBlock" Property="Foreground" Value="Green"/>
                        <Setter Property="TreeViewItem.IsExpanded" Value="True" />
                    </DataTrigger>
                </HierarchicalDataTemplate.Triggers>
            </HierarchicalDataTemplate>
        </DockPanel.Resources>

        <Button Name="button1" Click="button1_Click" DockPanel.Dock="Top" Content="Button1"/>
        <TreeView Name="treeView1" ItemsSource="{Binding MyItems}" ItemTemplate="{StaticResource MyTemplate}"/>
    </DockPanel>
</Window>

完整代码 (C#)

using System;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Windows;

namespace WpfApplication6
{
    public partial class MainWindow : Window
    {
        private ObservableCollection<MyItemCollection> _myItems;

        public MainWindow() {
            InitializeComponent();

            _myItems = new ObservableCollection<MyItemCollection> {
                new MyItemCollection { Name = "Parent1", MyStatus = MyStatus.Closed, SubItems = { new MyItemCollection { Name = "Child1" } } },
                new MyItemCollection { Name = "Parent2", MyStatus = MyStatus.Opened, SubItems = { new MyItemCollection { Name = "Child2" } } }
            };

            DataContext = new {
                MyItems = _myItems
            };
        }

        private void button1_Click(object sender, RoutedEventArgs e) {
            _myItems[0].MyStatus = MyStatus.Opened;
            _myItems[1].MyStatus = MyStatus.Closed;
        }
    }

    public enum MyStatus
    {
        Closed,
        Opened
    }

    public class MyItemCollection : INotifyPropertyChanged
    {
        public MyItemCollection() {
            SubItems = new ObservableCollection<MyItemCollection>();
            _myStatus = MyStatus.Closed;
        }

        public string Name { get; set; }

        public ObservableCollection<MyItemCollection> SubItems { get; set; }

        private MyStatus _myStatus;
        public MyStatus MyStatus {
            get { return _myStatus; }
            set { _myStatus = value; NotifyPropertyChanged("MyStatus"); }
        }

        public event PropertyChangedEventHandler PropertyChanged;
        private void NotifyPropertyChanged(String propertyName) {
            PropertyChangedEventHandler handler = PropertyChanged;
            if (handler != null) {
                handler(this, new PropertyChangedEventArgs(propertyName));
            }
        }
    }
}

Answer 1

这里有一些问题。第一个是您在HierarchicalDataTemplate 上设置属性TreeViewItem.IsSelected。这行不通。相反，您需要在TreeView 上设置ItemContainerStyle：

<TreeView>
    <TreeView.ItemContainerStyle>
        <Style TargetType="{x:Type TreeViewItem}">
        <!-- put logic for handling expansion here -->
        </Style>
    </TreeView.ItemContainerStyle>
</TreeView>

但是，您不能只将Trigger 放在这里。由于DependencyProperty value precedence，如果您的用户单击节点以展开或折叠它们，您的触发器将不会在优先级列表中排名第一（即本地值）。因此，最好的办法是创建一个新的IValueConverter 以将MyStatus 转换为bool。然后在Style 中的Setter 中设置TwoWay 绑定：

<Style TargetType="{x:Type TreeViewItem}">
    <Setter Property="IsExpanded" 
            Value="{Binding MyStatus, Converter={StaticResource statusToBool}}" />
</Style>

还有你的转换器：

public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
    return ((MyStatus)value) == MyStatus.Opened;
}

public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
    return ((bool)value) ? MyStatus.Opened : MyStatus.Closed;
}

Answer 2

我不得不做类似的事情，我是这样解决的：

<TreeView ItemsSource="{Binding source}"
          SnapsToDevicePixels="{Binding Path=myStatusToBool}"
          >
  <TreeView.ItemContainerStyle>
    <Style>
      <Setter Property="TreeViewItem.IsExpanded"
              Value="False"
              />
      <Style.Triggers>
        <DataTrigger Binding="{Binding Path=SnapsToDevicePixels,RelativeSource={RelativeSource AncestorType=TreeView}}"
                     Value="True">
            <Setter Property="TreeViewItem.IsExpanded"
                    Value="True"
                    />
        </DataTrigger>
      </Style.Triggers>
    </Style>
  </TreeView.ItemContainerStyle>

  <TreeView.Resources>
  .....
  .....
  </TreeView.Resources>
</TreeView>

Answer 3

我遇到了同样的问题，但没有使用值转换器就解决了：

                    <TreeView.ItemContainerStyle>
                        <Style TargetType="{x:Type TreeViewItem}" BasedOn="{StaticResource {x:Type TreeViewItem}}">
                            <Style.Triggers>
                                <DataTrigger Binding="{Binding IsVisible}" Value="False">
                                    <Setter Property="Visibility" Value="Collapsed" />
                                </DataTrigger>
                                <DataTrigger Binding="{Binding IsExpanded}" Value="True">
                                    <Setter Property="IsExpanded" Value="True" />
                                </DataTrigger>
                            </Style.Triggers>
                        </Style>
                    </TreeView.ItemContainerStyle>