CollectionViewSource没有更新属性改变

我在xaml中使用CollectionViewSource, c#将该CollectionViewSource的源设置为一个ObservableCollection类，该类是页面的数据上下文。向集合中添加项不会更新包含显示视图源的DataGridComboBox列。查看下面的行

我有一个WPF页面上的数据网格。该页将其数据上下文设置为视图模型。viewModel包含两个可观察集合。一个用于设备，一个用于位置。每个装备都有一个位置。这些是由代码优先的EF数据库填充的，但我相信这个问题超出了这个级别。

数据网格是每个装备一行。位置列需要是一个可选择的组合框，允许用户更改位置。

唯一可以让位置组合框填充的方法是将它绑定到一个单独的集合视图源。

似乎，如果页面加载事件发生在ViewModel填充ObservableCollection之前，那么locationVwSrc将是空的，属性改变的事件不会让这个改变。

实现简版页面有一个在xaml.

Loaded="Page_Loaded"
  Title="EquipRegPage">
<Page.Resources>
    <CollectionViewSource x:Key="locationsVwSrc"/>
</Page.Resources>

数据网格是用xaml定义的。

<DataGrid x:Name="equipsDataGrid" RowDetailsVisibilityMode="VisibleWhenSelected" Margin="10,10,-118,59" 
              ItemsSource="{Binding Equips}" EnableRowVirtualization="True" AutoGenerateColumns="False">

在xaml

<DataGridComboBoxColumn x:Name="locationColumn" Width="Auto" MaxWidth="200" Header="Location"
                                    ItemsSource="{Binding Source={StaticResource locationsVwSrc}, UpdateSourceTrigger=PropertyChanged}"
                                    DisplayMemberPath="Name"
                                    SelectedValueBinding="{Binding Location}"

设置为视图模型的页面上下文

public partial class EquipRegPage : Page
{
    EquipRegVm viewModel = new EquipRegVm();
    public EquipRegPage()
    {
        InitializeComponent();
        this.DataContext = viewModel;
    }

加载事件设置上下文

private void Page_Loaded(object sender, RoutedEventArgs e)
    {
        // Locations View Source
        System.Windows.Data.CollectionViewSource locationViewSource =
            ((System.Windows.Data.CollectionViewSource)(this.FindResource("locationsVwSrc")));
        locationViewSource.Source = viewModel.Locations;
        // Above does not work if the viewmodel populates these after this call, only works if its populated prior.
        //TODO inotifypropertychanged not correct? This occurs before the viewmodels loads, and doesn't display.
        // Therefore notify property changes aren't working.
        // Using this as cheat instead instead works, i beleive due to this only setting the source when its full
        //viewModel.Db.Locations.Load();
        //locationViewSource.Source = viewModel.Db.Locations.Local;
        //locationViewSource.View.Refresh();
    }

ViewModel类和它如何加载

public class EquipRegVm : DbWrap, INotifyPropertyChanged
{
    /// <summary>
    /// Event triggered by changes to properties. This notifys the WPF UI above which then 
    /// makes a binding to the UI.
    /// </summary>
    public event PropertyChangedEventHandler PropertyChanged;
    /// <summary>
    /// Notify Property Changed Event Trigger
    /// </summary>
    /// <param name="propertyName">Name of the property changed. Must match the binding path of the XAML.</param>
    void RaisePropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }

    public ObservableCollection<Equip> Equips { get; set; }
    public ObservableCollection<Location> Locations { get; set; }
    public EquipRegVm() : base()
    {
        Load();
    }
    /// <summary>
    /// Load the data from the Model.
    /// </summary>
    public async void Load()    //TODO async an issue?
    {
        // EQUIPMENT
        ObservableCollection<Equip> eqList = new ObservableCollection<Equip>();
        var eqs = await (from eq in Db.Equips
                        orderby eq.Tag
                        select eq).ToListAsync();
        foreach(var eq in eqs)
        {
            eqList.Add(eq);
        }
        Equips = eqList;
        RaisePropertyChanged("Equips");

        // LOCATIONS
        ObservableCollection<Location> locList = new ObservableCollection<Location>();
        var locs = await (from l in Db.Locations
                         orderby l.Name
                         select l).ToListAsync();
        foreach (var l in locs)
        {
            locList.Add(l);
        }
        Locations = locList;
        RaisePropertyChanged("Locations");
    }
}