尝试重现该问题并实现了在节点展开且一切正常时调用命令的附加行为。解决方案的完整代码：
XAML
<Window x:Class="TreeViewTest.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:sotc="clr-namespace:TreeViewTest"
mc:Ignorable="d"
Title="MainWindow" Height="350" Width="525">
<Window.DataContext>
<sotc:MainWindowViewModel />
</Window.DataContext>
<Grid>
<TreeView Name="ScenariosTreeView" ItemsSource="{Binding Path=Cat, Mode=TwoWay}" Focusable="True" >
<TreeView.InputBindings>
<KeyBinding Key="Delete" Command="{Binding DeleteCommand}" CommandParameter="{Binding SelectedValue ,ElementName=ScenariosTreeView}" />
</TreeView.InputBindings>
<TreeView.ItemContainerStyle>
<Style TargetType="{x:Type TreeViewItem}">
<Setter Property="IsExpanded" Value="{Binding IsExtended, Mode=TwoWay}" />
<Setter Property="IsSelected" Value="{Binding IsSelected, Mode=TwoWay}"/>
<Setter Property="sotc:Behaviours.ExpandingBehaviour" Value="{Binding DataContext.ExpandingCommand, RelativeSource={RelativeSource AncestorType=Window}}"/>
</Style>
</TreeView.ItemContainerStyle>
<TreeView.Resources>
<HierarchicalDataTemplate DataType="{x:Type sotc:ScenarioCategory}" ItemsSource="{Binding Path=ScenarioList}" >
<TextBlock Text="{Binding Path=Name}" Foreground="Black" IsEnabled="True" Focusable="True"/>
</HierarchicalDataTemplate>
<DataTemplate DataType="{x:Type sotc:Scenario}" >
<TextBlock Text="{Binding Path=Name, Mode=TwoWay}" />
</DataTemplate>
</TreeView.Resources>
</TreeView>
</Grid>
</Window>
C#
public class ViewModelBase : INotifyPropertyChanged
{
public void OnPropertyChanged([CallerMemberName] string name = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));
}
public event PropertyChangedEventHandler PropertyChanged;
}
public class MainWindowViewModel : ViewModelBase
{
public ICommand ExpandingCommand { get; set; }
private void ExecuteExpandingCommand(object obj)
{
Console.WriteLine(@"Expanded");
}
private bool CanExecuteExpandingCommand(object obj)
{
return true;
}
public MainWindowViewModel()
{
ExpandingCommand = new RelayCommand(ExecuteExpandingCommand, CanExecuteExpandingCommand);
Cat = new ObservableCollection<ScenarioCategory>(new ScenarioCategory[]
{
new ScenarioCategory { Name = "C1" }, new ScenarioCategory { Name = "C2" }, new ScenarioCategory { Name = "C3" }
});
}
public ObservableCollection<ScenarioCategory> Cat { get; set; }
}
public class ScenarioCategory : ViewModelBase
{
string _name;
public string Name
{
get { return _name; }
set { _name = value; OnPropertyChanged(); }
}
bool _isExtended;
public bool IsExtended
{
get { return _isExtended; }
set
{
_isExtended = value;
Console.WriteLine(@"IsExtended set");
OnPropertyChanged();
}
}
bool _isSelected;
public bool IsSelected
{
get { return _isSelected; }
set
{
_isSelected = value;
Console.WriteLine(@"IsSelected set");
OnPropertyChanged();
}
}
public ObservableCollection<Scenario> ScenarioList { get; set; }
public ScenarioCategory()
{
ScenarioList = new ObservableCollection<Scenario>(new Scenario[] { new Scenario { Name = "1" }, new Scenario { Name = "2" }, new Scenario { Name = "3" } });
}
}
public class Scenario : ViewModelBase
{
string _name;
public string Name
{
get { return _name; }
set { _name = value; OnPropertyChanged(); }
}
bool _isExtended;
public bool IsExtended
{
get { return _isExtended; }
set
{
_isExtended = value;
OnPropertyChanged();
}
}
bool _isSelected;
public bool IsSelected
{
get { return _isSelected; }
set
{
_isSelected = value;
OnPropertyChanged();
}
}
}
public static class Behaviours
{
public static readonly DependencyProperty ExpandingBehaviourProperty =
DependencyProperty.RegisterAttached("ExpandingBehaviour", typeof(ICommand), typeof(Behaviours),
new PropertyMetadata(OnExpandingBehaviourChanged));
public static void SetExpandingBehaviour(DependencyObject o, ICommand value)
{
o.SetValue(ExpandingBehaviourProperty, value);
}
public static ICommand GetExpandingBehaviour(DependencyObject o)
{
return (ICommand)o.GetValue(ExpandingBehaviourProperty);
}
private static void OnExpandingBehaviourChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
TreeViewItem tvi = d as TreeViewItem;
if (tvi != null)
{
ICommand ic = e.NewValue as ICommand;
if (ic != null)
{
tvi.Expanded += (s, a) =>
{
if (ic.CanExecute(a))
{
ic.Execute(a);
}
a.Handled = true;
};
}
}
}
}
public class RelayCommand : ICommand
{
private Action<object> execute;
private Func<object, bool> canExecute;
public event EventHandler CanExecuteChanged
{
add { CommandManager.RequerySuggested += value; }
remove { CommandManager.RequerySuggested -= value; }
}
public RelayCommand(Action<object> execute, Func<object, bool> canExecute = null)
{
this.execute = execute;
this.canExecute = canExecute;
}
public bool CanExecute(object parameter)
{
return this.canExecute == null || this.canExecute(parameter);
}
public void Execute(object parameter)
{
this.execute(parameter);
}
}