Question

我在这个非常好的article的帮助下构建了一个treeView WPF MVVM 然后我为某个节点创建了一个contextMenu，允许我从选定的父节点添加子节点。

问题是如果我点击＆＃34;添加＆＃34;如果不手动扩展所选节点（父节点），除了在点击＆＃34;添加＆＃34;时预期生成的节点之外，还会自动创建一个奇怪的子节点。

我尝试检测到问题，因此我更改了以下代码：

<Setter Property="IsExpanded" Value="{Binding IsExpanded, Mode=TwoWay}" />

为：

<Setter Property="IsExpanded" Value="True" />

下面的图1显示了此测试的结果，或者图2显示了我的treeView必须显示的内容。

image1的
IMAGE2

Rq：我使用了我所谈到的article中的图片。另外，我使用了本文中描述的相同方法（包括类TreeViewItemViewModel.cs）

所有ViewModel的基类

公共类TreeViewItemViewModel：INotifyPropertyChanged { #region数据

static readonly TreeViewItemViewModel DummyChild = new TreeViewItemViewModel();

readonly ObservableCollection<TreeViewItemViewModel> _children;
readonly TreeViewItemViewModel _parent;

bool _isExpanded;
bool _isSelected;

#endregion // Data

#region Constructors

protected TreeViewItemViewModel(TreeViewItemViewModel parent, bool lazyLoadChildren)
{
    _parent = parent;

    _children = new ObservableCollection<TreeViewItemViewModel>();

    if (lazyLoadChildren)
        _children.Add(DummyChild);
}

// This is used to create the DummyChild instance.
private TreeViewItemViewModel()
{
}

#endregion // Constructors

#region Presentation Members

#region Children

/// <summary>
/// Returns the logical child items of this object.
/// </summary>
public ObservableCollection<TreeViewItemViewModel> Children
{
    get { return _children; }
}

#endregion // Children

#region HasLoadedChildren

/// <summary>
/// Returns true if this object's Children have not yet been populated.
/// </summary>
public bool HasDummyChild
{
    get { return this.Children.Count == 1 && this.Children[0] == DummyChild; }
}

#endregion // HasLoadedChildren

#region IsExpanded

/// <summary>
/// Gets/sets whether the TreeViewItem 
/// associated with this object is expanded.
/// </summary>
public bool IsExpanded
{
    get { return _isExpanded; }
    set
    {
        if (value != _isExpanded)
        {
            _isExpanded = value;
            this.OnPropertyChanged("IsExpanded");
        }

        // Expand all the way up to the root.
        if (_isExpanded && _parent != null)
            _parent.IsExpanded = true;

        // Lazy load the child items, if necessary.
        if (this.HasDummyChild)
        {
            this.Children.Remove(DummyChild);
            this.LoadChildren();
        }
    }
}

#endregion // IsExpanded

#region IsSelected

/// <summary>
/// Gets/sets whether the TreeViewItem 
/// associated with this object is selected.
/// </summary>
public bool IsSelected
{
    get { return _isSelected; }
    set
    {
        if (value != _isSelected)
        {
            _isSelected = value;
            this.OnPropertyChanged("IsSelected");
        }
    }
}

#endregion // IsSelected

#region LoadChildren

/// <summary>
/// Invoked when the child items need to be loaded on demand.
/// Subclasses can override this to populate the Children collection.
/// </summary>
protected virtual void LoadChildren()
{
}

#endregion // LoadChildren

#region Parent

public TreeViewItemViewModel Parent
{
    get { return _parent; }
}

#endregion // Parent

#endregion // Presentation Members

#region INotifyPropertyChanged Members

public event PropertyChangedEventHandler PropertyChanged;

protected virtual void OnPropertyChanged(string propertyName)
{
    if (this.PropertyChanged != null)
        this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}

#endregion // INotifyPropertyChanged Members

}

Myxml：

RegionViewModel：

`public class StateViewModel：TreeViewItemViewModel {

   readonly State _state;
   public ICommand AddCityCommand { get; private set; }
   public List<MenuItem> AddCityItems { get; set; }

    public StateViewModel(State state, RegionViewModel parentRegion)
        : base(parentRegion, true)
    {
        _state = state;
        AddCityItems = new List<MenuItem>();
        AddCityCommand = new DelegateCommand<CancelEventArgs>(OnAddCityCommandExecute, OnAddCityCommandCanExecute);
        AddCityItems.Add(new MenuItem() { Header = "Add City", Command = AddCityCommand });
    }

    public string StateName
    {
        get { return _state.StateName; }
    }

    protected override void LoadChildren()
    {
        foreach (City city in Database.GetCities(_state))
            base.Children.Add(new CityViewModel(city, this));
    }


    bool OnAddCityCommandCanExecute(CancelEventArgs parameter)
    {
        return true;
    }

    public void OnAddCityCommandExecute(CancelEventArgs parameter)
    {
        var myNewCity = new city();
        Children.Add(new CityViewModel(myNewCity, this));
    }
}`

顺便说一句，如果我展开我的父节点，然后点击添加城市，我得到了预期的结果但是如果我不扩展父节点并且我点击contextMenu我除了孩子之外还创建了另一个孩子我想创建

修改我将下面的statemnt添加到我的add（）方法中，现在我没有任何问题：

public void OnAddCityCommandExecute(CancelEventArgs parameter)
    {
        var myNewCity = new city();
        Children.Add(new CityViewModel(myNewCity, this));
        //the modif
        this.Children.Remove(DummyChild);
    }

Answer 1

我可以在你的代码中看到错误。

以下是重现的步骤：

在状态节点（从不首先展开它）
未预先扩展子项，StateViewModel的子项包含DummyChild。
在列表中添加了1个新城市，导致HasDummyChild无效，因为儿童列表中的计数现在为2
然后，当您尝试展开节点以检查结果时。您的树状人员将拥有DummyChild，这是一个搞砸了所有内容的基类

所以，基本上这就是为什么“扩展”首先是你的问题的关键，因为当时HasDummyChild仍在工作，因为它比较.Count == 1.如果添加，树将不会从你的子列表中删除DummyChild列表中的额外子项使.Count == 2.

根据要求提供其他信息

只需将HasDummyChild更改为以下

    public bool HasDummyChild
    {
        //get { return this.Children.Count == 1 && this.Children[0] == DummyChild; }
        get { return Children.Any() && Children.Contains(DummyChild); }
    }

我的treeView填充了一个奇怪的孩子：WPF MVVM

1 个答案: