我正在尝试编写一个多选择树视图行为，但是在这样做时我收到了这个神秘的错误“在使用 ItemsSource 之前，项目集合必须为空。”
以下是我的 xaml 代码：
<Window x:Class="TreeView.Spike.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:Spike="clr-namespace:TreeView.Spike"
Title="MainWindow" Height="350" Width="525">
<Window.Resources>
</Window.Resources>
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width=".5*"/>
<ColumnDefinition Width=".5*"/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="*"></RowDefinition>
<RowDefinition Height="40"></RowDefinition>
</Grid.RowDefinitions>
<TreeView ItemsSource="{Binding Nodes}" Grid.Row="0" x:Name="treeView" Grid.Column="0">
<TreeView.ItemTemplate>
<HierarchicalDataTemplate ItemsSource="{Binding Nodes}">
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding Name}">
</TextBlock>
</StackPanel>
</HierarchicalDataTemplate>
</TreeView.ItemTemplate>
<TreeView.ContextMenu>
<ContextMenu>
<MenuItem Header="Add"></MenuItem>
<MenuItem Header="Delete"></MenuItem>
</ContextMenu>
</TreeView.ContextMenu>
<Spike:MultipleItemSelectionAttachedBehavior AllSelectedItems="{Binding Path=AllSelectedNodes}"/>
</TreeView>
</Grid>
</Window>
我的附加行为：
public class MultipleItemSelectionAttachedBehavior:Behavior<System.Windows.Controls.TreeView>
{
public static DependencyProperty AllSelectedItemsProperty =
DependencyProperty.RegisterAttached("AllSelectedItems", typeof(object), typeof(MultipleItemSelectionAttachedBehavior),
new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault | FrameworkPropertyMetadataOptions.Inherits));
private static readonly PropertyInfo IsSelectionChangeActiveProperty = typeof(System.Windows.Controls.TreeView).GetProperty("IsSelectionChangeActive",
BindingFlags.NonPublic | BindingFlags.Instance);
public object AllSelectedItems
{
get
{
return (object)GetValue(AllSelectedItemsProperty);
}
set
{
SetValue(AllSelectedItemsProperty, value);
}
}
public static bool GetAllSelectedItems(DependencyObject obj)
{
return (bool)obj.GetValue(AllSelectedItemsProperty);
}
public static void SetAllSelectedItems(DependencyObject obj, bool value)
{
obj.SetValue(AllSelectedItemsProperty, value);
}
protected override void OnAttached()
{
base.OnAttached();
AssociatedObject.SelectedItemChanged += AssociatedObject_SelectedItemChanged;
}
protected override void OnDetaching()
{
base.OnDetaching();
AssociatedObject.SelectedItemChanged -= AssociatedObject_SelectedItemChanged;
}
void AssociatedObject_SelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e)
{
if (IsSelectionChangeActiveProperty == null) return;
var selectedItems = new List<Node>();
var treeViewItem = AssociatedObject.SelectedItem as Node;
if (treeViewItem == null) return;
// allow multiple selection
// when control key is pressed
if (Keyboard.IsKeyDown(Key.LeftCtrl) || Keyboard.IsKeyDown(Key.RightCtrl))
{
var isSelectionChangeActive = IsSelectionChangeActiveProperty.GetValue(AssociatedObject, null);
IsSelectionChangeActiveProperty.SetValue(AssociatedObject, true, null);
selectedItems.ForEach(item => item.IsSelected = true);
IsSelectionChangeActiveProperty.SetValue(AssociatedObject, isSelectionChangeActive, null);
}
else
{
// deselect all selected items except the current one
selectedItems.ForEach(item => item.IsSelected = (item == treeViewItem));
selectedItems.Clear();
}
if (!selectedItems.Contains(treeViewItem))
{
selectedItems.Add(treeViewItem);
}
else
{
// deselect if already selected
treeViewItem.IsSelected = false;
selectedItems.Remove(treeViewItem);
}
AllSelectedItems = selectedItems;
}
}
..和我的 ViewModel
public class ViewModel :NotificationObject
{
public ViewModel()
{
AllSelectedNodes = new ObservableCollection<Node>();
}
private ObservableCollection<Node> _allSelectedNodes;
public ObservableCollection<Node> AllSelectedNodes
{
get { return _allSelectedNodes; }
set
{
_allSelectedNodes = value;
RaisePropertyChanged(() => AllSelectedNodes);
}
}
}
我的模型：
public class Node:NotificationObject
{
private string _name;
public string Name
{
get { return _name; }
set
{
_name = value;
RaisePropertyChanged(() => Name);
}
}
private bool _isExpanded = true;
public bool IsExpanded
{
get { return _isExpanded; }
set
{
_isExpanded = value;
RaisePropertyChanged(() => IsExpanded);
}
}
private bool _isSelected;
public bool IsSelected
{
get { return _isSelected; }
set
{
_isSelected = value;
RaisePropertyChanged(() => IsSelected);
}
}
private ObservableCollection<Node> _nodes;
public ObservableCollection<Node> Nodes
{
get { return _nodes; }
set
{
_nodes = value;
RaisePropertyChanged(() => Nodes);
}
}
public static IList<Node> Create()
{
return new List<Node>()
{
new Node()
{
Name = "Activity",
Nodes = new ObservableCollection<Node>()
{
new Node() {Name = "Company",Nodes = new ObservableCollection<Node>(){ new Node() {Name = "Company1",Existing = false}}},
new Node() {Name = "Strategy",Nodes = new ObservableCollection<Node>(){ new Node() {Name = "Strategy1"}}},
new Node() {Name = "Vehicle",Nodes = new ObservableCollection<Node>(){ new Node() {Name = "Vehicle1",Existing = false}}}
}
}
};
}
}
..和我的初始化代码：
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
var viewModel = new ViewModel();
this.DataContext = viewModel;
viewModel.Nodes = new ObservableCollection<Node>(Node.Create());
}
}
我不知道这里出了什么问题，你能帮忙吗？