c# - TreeView 未存储预期状态

Question

我遇到了以下我不理解的行为。我的数据正确显示在 TreeView 中，如下所示。

Sport
  > BaseBall
    > Apparel
    > Equiptment
        Glove
        Bat
  > Football
    > Helmet
  > Soccer

However, when I click on any node, the underlying node data is that of it's first child.

    Node Clicked            Actual Data
-------------------------------------------
    Sport                       Baseball
    Baseball                    Apparel
    Football                    Helmet
    Bat                         null

I have looked at many examples on the web and in books, but I cannot spot the issue; and I'm sure it's very simple.

Edit I have visually inspected each node in the debugger, as well as using a handy little code snippet from Mathew MacDonald's Pro WPF in C# 2010 that actually displays the types and value of every control in the TreeView.

Edit I have replaced initial code with an actual full application that reproduces the issue. It is the simplest example I could come up with.

The code(irrelevant sections removed):

<Application x:Class="WpfApplication1.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:this="clr-namespace:WpfApplication1"
             StartupUri="MainWindow.xaml">
    <Application.Resources>
        <this:MainWindowViewModel x:Key="ViewModel:MainWindow"></this:MainWindowViewModel>
    </Application.Resources>
</Application>

-

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:this="clr-namespace:WpfApplication1"
        Title="MainWindow" Height="350" Width="525"
        DataContext="{StaticResource ViewModel:MainWindow}">
    <TreeView x:Name="theTree" ItemsSource="{Binding Path=OrgChart}"
              MouseUp="theTree_MouseUp">
        <TreeView.Resources>
            <HierarchicalDataTemplate ItemsSource="{Binding Path=Subordinates}" DataType="{x:Type this:OrgChartNodeViewModel}">
                <TextBlock Text="{Binding Path=Position.Title}"></TextBlock>
            </HierarchicalDataTemplate>
        </TreeView.Resources>
    </TreeView>
</Window>

-

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }

    private void theTree_MouseUp(object sender, MouseButtonEventArgs e)
    {
        Stack<DependencyObject> stack = new Stack<DependencyObject>();
        var it = e.OriginalSource as DependencyObject;
        while (it != null)
        {
            it = VisualTreeHelper.GetParent(it);
            stack.Push(it);
        }

        int level = 0;
        while (stack.Any())
        {
            Debug.Write("".PadLeft(level++));
            it = stack.Pop();
            if (it is TreeViewItem)
            {
                var item = it as TreeViewItem;
                OrgChartNodeViewModel vm = ((OrgChartNodeViewModel)((TreeViewItem)it).Items.CurrentItem);
                if (vm != null)
                    Debug.WriteLine(vm.Position.Title);
            }
            else
            {
                Debug.WriteLine(it);
            }
        }
    }
}

-

public class MainWindowViewModel
{
    public List<OrgChartNodeViewModel> OrgChart { get; set; }

    public MainWindowViewModel()
    {
        Position ceo = new Position { Title = "CEO" };
        Position vp = new Position { Title = "VP" };
        Position boss = new Position { Title = "Boss" };
        Position worker = new Position { Title = "Worker" };

        OrgChartNodeViewModel root;
        OrgChartNodeViewModel node = new OrgChartNodeViewModel { Position = ceo };
        OrgChartNodeViewModel child = new OrgChartNodeViewModel { Position = vp };
        root = node;
        node.Subordinates.Add(child);
        node = child;
        child = new OrgChartNodeViewModel { Position = boss };
        node.Subordinates.Add(child);
        node = child;
        child = new OrgChartNodeViewModel { Position = worker };
        node.Subordinates.Add(child);

        OrgChart = new List<OrgChartNodeViewModel> { root };
    }
}

-

public class OrgChartNodeViewModel
{
    public Position Position { get; set; }
    public List<OrgChartNodeViewModel> Subordinates { get; set; }

    public OrgChartNodeViewModel()
    {
        Subordinates = new List<OrgChartNodeViewModel>();
    }
}

-

public class Position
{
    public string Title { get; set; }
}

这是我机器上的输出...

Answer 1

尝试切换

OrgChartNodeViewModel vm = ((OrgChartNodeViewModel)((TreeViewItem)it).Items.CurrentItem);

到

OrgChartNodeViewModel vm = ((OrgChartNodeViewModel)viewItem.DataContext);

在您的 while 循环中，您需要 TreeViewItem.DataContext 而不是 Items.CurrentItem ，它指向它的子项(只有一个存在直到第一次展开)。这就是为什么您看到 VP 而不是 CEO。

我很可能将整个函数切换为类似的东西:

private void theTree_MouseUp(object sender, MouseButtonEventArgs e) {
  var clickedItem = e.OriginalSource as FrameworkElement;
  if (clickedItem == null)
    return;
  var chartNode = clickedItem.DataContext as OrgChartNodeViewModel;
  if (chartNode != null)
    Debug.WriteLine(chartNode.Position.Title);
}

而不是遍历 Visual-Tree 以获得 TreeViewItem。 DataContext 在您的 xaml 设置中被继承，所以不妨使用它来避免做多余的工作。