UWP TreeView 数据绑定和反映变化

Question

UWP TreeView 是否通过从 VM 拖放到关联的 ItemsSource 来反映项目的变化？例如，我将 TreeView 与 VM ObservableCollection 列表相关联。当我通过从 VM 执行命令来添加一些项目时，这些项目用新项目填充该集合，它们确实显示在 TreeView UI 中。但是，如果我在 TreeView 中拖放项目，底层列表不会改变吗？我究竟做错了什么？ TreeView 是否应该根据我的操作更新和可观察的集合？

这是我的虚拟机：

public class MySampleViewModel : MyBase 
{
    public ObservableCollection<FolderInfo> storageFolders { get; set; } = new ObservableCollection<FolderInfo>();

    public ICommand MyCommand { get; }

    public ICommand ChangeCommand { get; }

    public MySampleViewModel()
    {
        AddFilesFolders();
    }

    private void AddFilesFolders()
    {
        FolderInfo ff1 = new FolderInfo();
        ff1.FolderName = "Folder " + DateTime.Now.ToString();
        ff1.IsFolder = true;
        ff1.subFolders = new ObservableCollection<FolderInfo>();

        storageFolders.Add(ff1);

        FolderInfo ffkeko = new FolderInfo();
        ffkeko.FolderName = "subitem" + DateTime.Now.ToString();
        ffkeko.subFolders = new ObservableCollection<FolderInfo>();

        ff1.subFolders.Add(ffkeko);

        FolderInfo ff = new FolderInfo();
        ff.FolderName = "servername " + DateTime.Now.ToString();
        ff.subFolders = new ObservableCollection<FolderInfo>();

        storageFolders.Add(ff);
    }
}

public class MyBase : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    public void OnPropertyChanged([CallerMemberName]string propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

public class FolderInfo : MyBase
{
    private string _FolderName;
    public string FolderName
    {
        get { return _FolderName; }
        set
        {
            if (_FolderName != value)
            {
                _FolderName = value;
                OnPropertyChanged("FolderName");
            }
        }
    }

    private bool _IsFolder;
    public bool IsFolder
    {
        get { return _IsFolder; }
        set
        {
            if (_IsFolder != value)
            {
                _IsFolder = value;
                OnPropertyChanged("IsFolder");
            }
        }
    }

    public ObservableCollection<FolderInfo> subFolders { get; set; } = new ObservableCollection<FolderInfo>();

    public override string ToString()
    {
        return FolderName;
    }
}

这是我的 TreeView 的 XAML：

<localdata:MyTreeView 
x:Name="treeview" Grid.Row="2" ItemsSource="{Binding storageFolders,Mode=OneWay}" 
Style="{StaticResource TreeViewStyle1}"
/>

Answer 1

问题在于，当发生更改时，您实际上是为subFolders 属性分配了一个新的ObservableCollection<FolderInfo> 实例，但数据绑定绑定到前一个实例，因此它不会观察到此更改。这个问题有两种解决方案：

1) 更改实例并引发PropertyChanged 事件：

private ObservableCollection<FolderInfo> _subFolders = new ObservableCollection<FolderInfo>();
public ObservableCollection<FolderInfo> subFolders
{
   get => _subFolders;
   set
   {
      _subFolders = value;
      OnPropertyChanged();
   }
}

2) 不要分配新实例，而是清除原始实例并添加新项目：

所以而不是：

ff.subFolders = new ObservableCollection<FolderInfo>();
ff.subFolders.Add(something);

你会做的：

ff.subFolders.Clear();
ff.subFolders.Add(something);