为什么 collectionviewsource 在单击按钮时不更新数据网格

我有两个视图模型，一个是mainViewModel，另一个是parentViewModel。我将主视图模型设置为主窗口网格的数据上下文，并将父视图模型设置为数据网格的数据上下文。我尝试使用实体框架生成的模型来更新数据网格，但在实现 INotifyPropertyChange 时出现错误，因此我创建了一个自定义模型并将实体框架模型中的数据映射到我的自定义模型。

父视图模型：

在本例中，父类是实体框架生成的模型，父类是我的自定义模型。

public class ParentViewModel : INotifyPropertyChanged 
{
    #region Constructor
    /// <summary>
    /// Initializes a new instance of Parent ViewModel class.
    /// </summary>
    public ParentViewModel()
    {
        _addParentCommand = new AddParentCommand(AddParent, IsExecutable);
        Parentss = new Parents()
        {
            PLastName = null,
            PFirstName = null,
            PMiddleName = null,
            PAddress = null,
            PContactNo = null,
            PEmail = null,
            PUsername = null,
            PPassword = null,
            ValidationString = null
        };
        _parentCollection = new ObservableCollection<Parent>();
        _parentsCollection = new ObservableCollection<Parents>();
        //ParentsCollection = new ObservableCollection<Parents>();
        _parentList = new List<Parent>();
        _parentsList = new List<Parents>();
        ViewSource = new CollectionViewSource();
        ViewSource.Source = ParentsCollection;
        Load();
    }
    #endregion
    #region Events
    public event PropertyChangedEventHandler PropertyChanged;
    public void OnPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
    #endregion
    #region Methods
    /// <summary>
    /// Checks if the application can execute a method.
    /// </summary>
    /// <param name="context">Data context</param>
    /// <returns>bool</returns>
    public bool IsExecutable(object context)
    {
        if (context != null)
        {
            var s = context as string;
            s = s.Trim();
            if (string.IsNullOrWhiteSpace(s))
            {
                return false;
            }
            return true;
        }
        return false;
    }
    /// <summary>
    /// Loads the data from the database when the application starts.
    /// </summary>
    public void Load()
    {
        using (RegistrationEntities registrationContext = new RegistrationEntities())
        {
            _parentList = registrationContext.Parents.ToList();

            for (int i = 0; i < _parentList.Count; i++)
            {
                Parents = new Parents()
                {
                    PId = _parentList[i].P_Id,
                    PLastName = _parentList[i].P_LastName,
                    PFirstName = _parentList[i].P_FirstName,
                    PMiddleName = _parentList[i].P_MiddleName,
                    PAddress = _parentList[i].P_Address,
                    PContactNo = _parentList[i].P_ContactNo,
                    PEmail = _parentList[i].P_Email,
                    PUsername = _parentList[i].P_Username,
                    PPassword = _parentList[i].P_Password,
                    PCreatedOn = _parentList[i].P_CreatedOn,
                    PUpdatedAt = _parentList[i].P_UpdatedAt
                };
                _parentsCollection.Add(Parents);
                //ParentsCollection.Add(Parents);
            }
        }
    }
    public void Load2()
    {
        //for (int i = 0; i < _parentsList.Count; i++)
        //{
        //    _parentsCollection.Add(_parentsList[i]);
        //}
    }
    /// <summary>
    /// Add a new Parent.
    /// </summary>
    /// <param name="context">Data context</param>
    public void AddParent(object context)
    {
        using (RegistrationEntities registrationContext = new RegistrationEntities())
        {
            Parent parent = new Parent
            {
                P_LastName = Parentss.PLastName,
                P_FirstName = Parentss.PFirstName,
                P_MiddleName = Parentss.PMiddleName,
                P_Address = Parentss.PAddress,
                P_ContactNo = Parentss.PContactNo,
                P_Email = Parentss.PEmail,
                P_Username = Parentss.PUsername,
                P_Password = Encrypt(Parentss.PPassword),
                P_CreatedOn = DateTime.Now.Date + DateTime.Now.TimeOfDay,
                P_UpdatedAt = DateTime.Now.Date + DateTime.Now.TimeOfDay
            };
            registrationContext.Parents.Add(parent);
            try
            {
                registrationContext.SaveChanges();
                _parentList = registrationContext.Parents.ToList();
                _parentsCollection.Clear();
                //ParentsCollection.Clear();
                for (int i = 0; i < _parentList.Count; i++)
                {
                    Parents = new Parents()
                    {
                        PId = _parentList[i].P_Id,
                        PLastName = _parentList[i].P_LastName,
                        PFirstName = _parentList[i].P_FirstName,
                        PMiddleName = _parentList[i].P_MiddleName,
                        PAddress = _parentList[i].P_Address,
                        PContactNo = _parentList[i].P_ContactNo,
                        PEmail = _parentList[i].P_Email,
                        PUsername = _parentList[i].P_Username,
                        PPassword = _parentList[i].P_Password,
                        PCreatedOn = _parentList[i].P_CreatedOn,
                        PUpdatedAt = _parentList[i].P_UpdatedAt
                    };
                    _parentsCollection.Add(Parents);
                     ViewSource.View.Refresh();
                    //ParentsCollection.Add(Parents);
                }
                MessageBox.Show("Success!");
                Parentss.PLastName = null;
                Parentss.PFirstName = null;
                Parentss.PMiddleName = null;
                Parentss.PAddress = null;
                Parentss.PContactNo = null;
                Parentss.PEmail = null;
                Parentss.PUsername = null;
                Parentss.PPassword = null;
            }
            catch (DbEntityValidationException ex)
            {
                foreach (var eve in ex.EntityValidationErrors)
                {
                    MessageBox.Show(String.Format("Entity of type '"{0}'" in state '"{1}'" has the following validation errors: ", eve.Entry.Entity.GetType().Name, eve.Entry.State));
                    foreach (var ve in eve.ValidationErrors)
                    {
                        MessageBox.Show(String.Format("- Property: '"{0}'", Value: '"{1}'", Error: '"{2}'"", ve.PropertyName, eve.Entry.CurrentValues.GetValue<object>(ve.PropertyName), ve.ErrorMessage));
                    }
                }
            }
        }
    }
    public string Encrypt(string password)
    {
        MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();
        md5.ComputeHash(ASCIIEncoding.ASCII.GetBytes(password));
        byte[] result = md5.Hash;
        StringBuilder str = new StringBuilder();
        for (int i = 0; i < result.Length; i++)
        {
            str.Append(result[i].ToString("x2"));
        }
        return str.ToString();
    }
    #endregion
    #region Commands and Properties
    private ICommand _addParentCommand;
    /// <summary>
    /// Gets or sets an ICommand interface.
    /// </summary>
    public ICommand AddParentCommand
    {
        get { return _addParentCommand; }
        set { _addParentCommand = value; }
    }
    /// <summary>
    /// Gets or sets a Parent class.
    /// </summary>
    public Parents Parentss
    {
        get;
        set;
    }
    public Parents Parents
    {
        get;
        set;
    }
    private List<Parent> _parentList;
    public List<Parent> ParentList
    {
        get { return _parentList; }
        set { _parentList = value; OnPropertyChanged("ParentList"); }
    }
    private ObservableCollection<Parent> _parentCollection;
    public ObservableCollection<Parent> ParentCollection
    {
        get { return _parentCollection; }
        set { _parentCollection = value; }
    }
    private List<Parents> _parentsList;
    public List<Parents> ParentsList
    {
        get { return _parentsList; }
        set { _parentsList = value; }
    }
    private ObservableCollection<Parents> _parentsCollection;
    public ObservableCollection<Parents> ParentsCollection
    {
        get { return _parentsCollection; }
        set { _parentsCollection = value; }
    }
    public CollectionViewSource ViewSource { get; set; }
    #endregion
}

XAML：

 <Grid DataContext="{StaticResource mainViewModel}">
<DataGrid x:Name="dgvParent" Grid.Row="1" HorizontalAlignment="Stretch" Height="Auto" VerticalAlignment="Stretch" Width="Auto" SelectionMode="Single" BorderThickness="2" Style="{StaticResource AzureDataGrid}" AutoGenerateColumns="False" AlternatingRowBackground="LightBlue" ItemsSource="{Binding ViewSource.View}" DataContext="{DynamicResource parentViewModel}" CanUserAddRows="False">
                    <DataGrid.Columns>
                        <DataGridTextColumn Binding="{Binding PId}" FontWeight="Bold" Header="Id" />
                        <DataGridTextColumn Binding="{Binding PLastName}" FontWeight="Bold" Header="Last Name" />
                        <DataGridTextColumn Binding="{Binding PFirstName}" FontWeight="Bold" Header="First Name" />
                        <DataGridTextColumn Binding="{Binding PMiddleName}" FontWeight="Bold" Header="Middle Name" />
                        <DataGridTextColumn Binding="{Binding PAddress}" FontWeight="Bold" Header="Address" />
                        <DataGridTextColumn Binding="{Binding PContactNo}" FontWeight="Bold" Header="Contact Number" />
                        <DataGridTextColumn Binding="{Binding PEmail}" FontWeight="Bold" Header="Email" />
                        <DataGridTextColumn Binding="{Binding PCreatedOn}" FontWeight="Bold" Header="Created On" />
                        <DataGridTextColumn Binding="{Binding PUpdatedAt}" FontWeight="Bold" Header="Updated At" />
                    </DataGrid.Columns>
                </DataGrid>

public ICollectionView MyView{ get; set; }
//ctor
public ParentViewModel()
{
    //...
    ParentsCollection= new ObservableCollection<Parents>();
    MyView= CollectionViewSource.GetDefaultView(ParentsCollection);
    //...
}

<DataGrid ItemsSource="{Binding MyView}"/>