当从另一个窗口修改 ObservableCollection 时，绑定到 ObservableCollection 的 MainWindow 中的 MVVM WPF TreeView 不会更新

Question

该问题可能类似于此 但是，如果在同一窗口中修改 ObservableCollection （如链接帖子的情况），则更新 TreeView 不会有问题。

我的MainWindow 中有一个TreeView。我对 TreeView 使用 HierarchicalDataTemplate，基本上 TreeView 分为三个层次结构：组、报表、节点

对于 TreeView 的每个级别，我创建了简单的模型类，每个类都有一个Name 属性及其子类的 ObservableCollection 作为第二个属性（例如，Group 类将具有 Name 和 ReportList 属性，而 Report 类将具有 Name 和 NodeList 属性）

在我的 ViewModel 中MainWindow，我有一个绑定到 TreeView 的 Group 对象的 ObservableCollection（我将其命名为 Groups）。我还有一个 RelayCommand 方法，它将向 Groups 集合添加一个新的 Group 对象（我们将其称为 ImportReport 方法）。如果我将 RelayCommand 绑定到 MainWindow 内的按钮，则一切正常，每次按下按钮时，TreeView 都会立即更新为新的组对象。

但是，当我有另一个窗口（我们将其称为 ImportWindow）时，这就会成为问题。在 ImportWindow 中，我有一个按钮。可能这就是问题的原因，但是我对 ImportWindow 和 MainWindow 使用相同的 ViewModel，以便它们可以共享组绑定到 MainWindow 中 TreeView 的属性。我的目标是通过按第二个窗口中的按钮来执行对 TreeView 的添加。现在，如果我将 ImportReport 命令的绑定移动到 ImportWindow 中的按钮，然后尝试运行代码，按 ImportWindow 上的按钮根本不会更新 TreeView。我已经调试了代码，ViewModel 中的 Groups ObservableCollection 确实记录了新的添加，但 TreeView 不显示新的 Group 对象。

对此有何解释？谢谢！

主窗口

<Window x:Class="StressReportWPF.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:local="clr-namespace:StressReportWPF"
    xmlns:ribbon="clr-namespace:System.Windows.Controls.Ribbon;assembly=System.Windows.Controls.Ribbon"
    xmlns:viewModel="clr-namespace:StressReportWPF.ViewModel"
    xmlns:data="clr-namespace:StressReportWPF.DataElements"
    mc:Ignorable="d"
    Title="StressReportApp" 
    Height="750" 
    Width="1000">

<Window.DataContext>
    <viewModel:MainViewModel/>
</Window.DataContext>

<Window.Resources>
    <HierarchicalDataTemplate DataType="{x:Type data:DisplayGroup}"
                              ItemsSource="{Binding ReportList}">
        <TextBlock Text="{Binding DisplayGroupName}"/>
    </HierarchicalDataTemplate>

    <HierarchicalDataTemplate DataType="{x:Type data:DisplayReport}"
                              ItemsSource="{Binding NodeList}">
        <TextBlock Text="{Binding DisplayReportName}"/>
    </HierarchicalDataTemplate>

    <DataTemplate DataType="{x:Type data:DisplayNode}">
        <TextBlock Text="{Binding DisplayNodeName}"/>
    </DataTemplate>
</Window.Resources>

<Border Background="#e7f4fe">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="75"/>
            <RowDefinition/>
        </Grid.RowDefinitions>

        ...
        
        <Grid Grid.Row="1">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="250"/>
                <ColumnDefinition/>
            </Grid.ColumnDefinitions>

            <Border Grid.Column="0"
                    Margin="0,20,20,20"
                    Background="#dde6ed"
                    BorderBrush="Black"
                    BorderThickness="1">
                <ScrollViewer>
                    <TreeView Background="Transparent"
                              ItemsSource="{Binding Groups, UpdateSourceTrigger=PropertyChanged}">
                        
                    </TreeView>
                </ScrollViewer>
            </Border>

            <Border Grid.Column="1"
                    Margin="20,20,0,20"
                    Background="White"
                    BorderBrush="Black"
                    BorderThickness="1">

                <ContentControl Margin="0"
                                Content="{Binding CurrentView}">
                    
                </ContentControl>
            </Border>
            
        </Grid>
    </Grid>
    
    
</Border>

导入窗口

<Window x:Class="StressReportWPF.ImportWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:local="clr-namespace:StressReportWPF"
    xmlns:viewModel="clr-namespace:StressReportWPF.ViewModel"
    xmlns:data="clr-namespace:StressReportWPF.DataElements"
    xmlns:i="http://schemas.microsoft.com/xaml/behaviors"
    mc:Ignorable="d"
    Title="ImportWindow" Height="450" Width="800"
    Background="#dde6ed">

<Window.Resources>
    <BooleanToVisibilityConverter x:Key="BoolToVisConverter"/>
    
    <DataTemplate x:Key="GroupComboBoxTemplate">
        <TextBlock Text="{Binding DisplayGroupName}"/>
    </DataTemplate>
    
</Window.Resources>

<Window.DataContext>
    <viewModel:MainViewModel/>
</Window.DataContext>

<Grid>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="500"/>
        <ColumnDefinition/>
    </Grid.ColumnDefinitions>

    ...

    <Grid Grid.Column="1">
        <Grid.RowDefinitions>
            <RowDefinition Height="200"/>
            <RowDefinition Height="150"/>
            <RowDefinition/>
        </Grid.RowDefinitions>
        
        ...

        <Button Grid.Row="2"
                HorizontalAlignment="Center"
                VerticalAlignment="Center"
                Height="40"
                Width="100"
                Content="Import"
                Style="{StaticResource StandardButtonStyle}"
                Command="{Binding ImportCommand}">
            <i:Interaction.Triggers>
                <i:EventTrigger EventName="Click">
                    <i:CallMethodAction MethodName="Close" 
                                        TargetObject="{Binding RelativeSource={RelativeSource
                                              Mode=FindAncestor,
                                              AncestorType=Window}}" />
                </i:EventTrigger>
            </i:Interaction.Triggers>

        </Button>
    </Grid>
    
</Grid>

ViewModel

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using StressReportWPF.Core;
using StressReportWPF.DataElements;
using System.Collections.ObjectModel;
using System.Windows.Input;
using StressReportWPF.Views;

namespace StressReportWPF.ViewModel
{
    public class MainViewModel: ObservableObject
    {

    #region ViewModel-related Properties
    public RelayCommand HomePageViewCommand { get; set; }
    public RelayCommand LoadCaseAssignmentViewCommand { get; set; }
    public RelayCommand JointNumberAssignmentViewCommand { get; set; }
    public HomePageViewModel HomePageVM { get; set; }
    public LoadCaseAssignmentViewModel LoadCaseAssignmentVM { get; set; }
    public JointNumberAssignmentViewModel JointNumberAssignmentVM { get; set; }

    private object _currentView;

    public object CurrentView
    {
        get { return _currentView; }
        set
        {
            _currentView = value;
            OnPropertyChanged();
        }
    }
    #endregion

    private ICommand _importCommand;

    public ICommand ImportCommand
    {
        get
        {
            if (_importCommand == null)
            {
                _importCommand = new RelayCommand(
                    param => ImportReport()
                );
            }
            return _importCommand;
        }
    }

    private ICommand _importWindowCommand;

    public ICommand ImportWindowCommand
    {
        get
        {
            if (_importWindowCommand == null)
            {
                _importWindowCommand = new RelayCommand(
                    param => ShowImportWindow()
                );
            }
            return _importWindowCommand;
        }
    }

    #region Data Properties
    private readonly ObservableCollection<DisplayGroup> _groups = new ObservableCollection<DisplayGroup>();

    public ObservableCollection<DisplayGroup> Groups
    {
        get { return _groups; }
    }

    public bool IsNewGroupCreated { get; set; }
    public object SelectedGroup { get; set; }

    private DisplayGroup _newGroup = new DisplayGroup();

    public DisplayGroup NewGroup
    {
        get { return _newGroup; }
        set
        {
            _newGroup = value;
            OnPropertyChanged();
        }
    }

    #endregion

    public MainViewModel()
    {
        HomePageVM = new HomePageViewModel();
        LoadCaseAssignmentVM = new LoadCaseAssignmentViewModel();
        JointNumberAssignmentVM = new JointNumberAssignmentViewModel();

        CurrentView = HomePageVM;

        HomePageViewCommand = new RelayCommand(o =>
        {
            CurrentView = HomePageVM;
        });
        LoadCaseAssignmentViewCommand = new RelayCommand(o =>
        {
            CurrentView = LoadCaseAssignmentVM;
        });
        JointNumberAssignmentViewCommand = new RelayCommand(o =>
        {
            CurrentView = JointNumberAssignmentVM;
        });

        // Set a temporary Group list
        List<DisplayGroup> testGroupList = new List<DisplayGroup>();
        List<DisplayNode> testNodeList = new List<DisplayNode>();
        List<DisplayReport> testReportList = new List<DisplayReport>();

        DisplayNode nodeA = new DisplayNode();
        nodeA.DisplayNodeName = "Node A";
        DisplayNode nodeB = new DisplayNode();
        nodeB.DisplayNodeName = "Node B";
        DisplayNode nodeC = new DisplayNode();
        nodeC.DisplayNodeName = "Node C";

        testNodeList.AddRange(new List<DisplayNode> { nodeA, nodeB, nodeC }) ;
        ObservableCollection<DisplayNode> testNodeObsCol = new ObservableCollection<DisplayNode>(testNodeList);

        DisplayReport reportA = new DisplayReport();
        reportA.DisplayReportName = "Report A";
        reportA.NodeList = testNodeObsCol;

        DisplayReport reportB = new DisplayReport();
        reportB.DisplayReportName = "Report B";
        reportB.NodeList = testNodeObsCol;

        DisplayReport reportC = new DisplayReport();
        reportC.DisplayReportName = "Report C";
        reportC.NodeList = testNodeObsCol;

        testReportList.AddRange(new List<DisplayReport> { reportA, reportB, reportC });
        ObservableCollection<DisplayReport> testReportObsCol = new ObservableCollection<DisplayReport>(testReportList);

        DisplayGroup groupA = new DisplayGroup();
        groupA.DisplayGroupName = "Group A";
        groupA.ReportList = testReportObsCol;

        DisplayGroup groupB = new DisplayGroup();
        groupB.DisplayGroupName = "Group B";
        groupB.ReportList = testReportObsCol;

        DisplayGroup groupC = new DisplayGroup();
        groupC.DisplayGroupName = "Group C";

        testGroupList.AddRange(new List<DisplayGroup> { groupA, groupB, groupC });

        foreach (var item in testGroupList)
        {
            Groups.Add(item);
        }
    }

    public void ShowImportWindow()
    {
        //ImportViewModel importVM = new ImportViewModel();
        //importVM.Groups = this.Groups;
        ImportWindow importWindow = new ImportWindow();
        //importWindow.DataContext = importVM;
        importWindow.Show();
    }
    public void ImportReport()
    {
        if (IsNewGroupCreated)
        {
            DisplayGroup newGroup = new DisplayGroup();
            newGroup.DisplayGroupName = "Group D";
            Groups.Add(newGroup);
        }
        else
        {

        }
    }
}
}