WPF TreeView，IsExpanded 的双向绑定不影响来自 C# 代码的 GUI

Question

我正在尝试创建一个可以在树层次结构中显示项目的 TreeView。我希望能够使用代码 (C#) 通过绑定到 ObservableCollection 的属性展开和折叠 TreeView 中的 TreeViewItems。

我已经将我的 class 的属性绑定到 IsExpanded，如果我在设置树的 ItemSource 之前设置它似乎可以工作 - 新创建的层次结构将预先展开。

但是，如果我单击为集合中的项目设置 IsExpanded 的按钮，它不会展开或折叠 GUI 中的树项目。

这是到目前为止该程序的丑陋屏幕截图。这些文件夹是在初始化过程中手动创建的。

这里是 TreeView xaml 主 window:

<TreeView x:Name="TheProjectTree" Margin="5" BorderBrush="{x:Null}" ItemsSource="{Binding DataSet}">
    <TreeView.ItemContainerStyle>
        <Style TargetType="{x:Type TreeViewItem}">
            <Setter Property="IsExpanded" Value="{Binding Path=IsExpanded, Mode=TwoWay}" />
            <!--<EventSetter Event="Expanded" Handler="TheProjectTreeItem_Expanded" />-->
        </Style>
    </TreeView.ItemContainerStyle>
    <TreeView.ItemTemplate>
        <HierarchicalDataTemplate ItemsSource="{Binding nodes}">
            <StackPanel Orientation="Horizontal">
                <Image Source="{Binding Path=Icon}" Height="16"/>
                <TextBlock Text=" " />
                <TextBlock Text="{Binding Path=Name}" />
                <TextBlock Text=" (" />
                <TextBlock Text="{Binding Path=Type}" />
                <TextBlock Text=")" />
            </StackPanel>
        </HierarchicalDataTemplate>
    </TreeView.ItemTemplate>
</TreeView>

这是一个 MyProject class，它具有以下数据结构：

using System.Collections.ObjectModel;

namespace Project_X
{
    public class MyProject
    {
        public ObservableCollection<MyNode> nodes;

        public MyProject()
        {

        }

        public void Initialize()
        {
            nodes = new ObservableCollection<MyNode>();
            nodes.Add(new MyNode("Untitled Project", "Project"));
            AddFolder("0. Initialize");
            AddFolder("1. Reset");
            AddFolder("2. Migrate");
        }

        public void AddFolder(string folderName)
        {
            nodes[0].nodes.Add(new MyProject.MyNode(folderName, "Folder"));
        }

        public class MyNode
        {
            public string Name { get; set; }
            public string Type { get; set; }
            public bool IsExpanded { get; set; }
            public ObservableCollection<MyNode> nodes { get; set; }
            public MyNode(string theName, string theType)
            {
                Name = theName;
                Type = theType;
                nodes = new ObservableCollection<MyNode>();
            }
            public string Icon
            {
                get
                {
                    if (Type == "Project")
                        return "./graphics/icon_projectTree_small.png";
                    else if (Type == "Folder")
                        return "./graphics/icon_projectTree_small.png";
                    else if (Type == "Object")
                        return "./graphics/icon_projectTree_small.png";
                    else if (Type == "SQL")
                        return "./graphics/icon_projectTree_small.png";
                    else if (Type == "Text")
                        return "./graphics/icon_projectTree_small.png";
                    return "./graphics/icon_projectTree_small.png";
                }
            }
        }
    }
}

最后，这是一个我可以从测试按钮调用的小测试程序。

private void NewProject()
{
    Project = new MyProject();                      // fire up the main project variable!
    Project.Initialize();                           // give it some dummy data!
    Project.nodes[0].IsExpanded = true;             // pre-expand the top-level project node
    TheProjectTree.ItemsSource = Project.nodes;     // assign the data set to the tree in the main window



    Project.AddFolder("test");                      // this works! adding new folders to the collection will show up in the GUI
    Project.nodes[0].IsExpanded = true;             // this does NOT work! it should collapse the top-levl project node in the tree, but it doesn't
}

如果你能给我一些知识，我将不胜感激。我通常在 SQL 工作，C# 和 .NET 不是我的强项。我整个晚上都在努力思考 MVVM 和天哪，我现在觉得自己是一个非常糟糕的程序员！

Answer 1

你的 MyNode class 需要实现 INotifyPropertyChanged 让 Gui 知道属性已经改变。然后在 IsExpanded 属性的 setter 中，您将不得不调用 NotifyPropertyChanged 已在给定的 link.

中进行了解释

Answer 2

为您的 MyNode Class 实现 INotifyPropertyChanged 接口。它通知属性值已更改。

public class MyNode : INotifyPropertyChanged
{
    private bool isExpanded;

    public string Name { get; set; }
    public string Type { get; set; }
    public bool IsExpanded
    {
        get => isExpanded;
        set
        {
            isExpanded = value;
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(IsExpanded)));
        }
    }
    public ObservableCollection<MyNode> nodes { get; set; }
    public MyNode(string theName, string theType)
    {
        Name = theName;
        Type = theType;
        nodes = new ObservableCollection<MyNode>();
    }

    public event PropertyChangedEventHandler PropertyChanged;
}

WPF TreeView，IsExpanded 的双向绑定不影响来自 C# 代码的 GUI

WPF TreeView, TwoWay binding for IsExpanded is not affecting GUI from C# code

.net

c#

wpf

treeview

binding