refresh datagrid on view from viewmodel

I have a datagrid on a view that is bound to a viewmodel. When I initialze the view, the datagrid is populated with data from the viewmodel (ObservableCollection) as it should. However, with I try to do a search against the data, the datagrid does not get refreshed from the viewmodel. When I breakpoint the code in my viewmodel, I can see the results in the ObservableCollection has changed per my search, but somehow that is not getting communicated back to the view. Here is my view and viewmodel (BTW, I am using VS2010 RTM):

namespace Attendance.ViewModels
{
    public class EmployeeSelectViewModel : ViewModel, INotifyPropertyChanged
    {
        #region Entity list and constructor
    public EmployeeSelectViewModel()
    {
        {
            Initialize();
        }
    }

    private void Initialize()
    {
        if (employeeRpository == null)
            employeeRpository = new EmployeeRepository();

        ListOfEmployees = new ObservableCollection<EmployeeDto>(employeeRpository.GetEmployees(true));
    }

    private EmployeeRepository employeeRpository;

    private ObservableCollection<EmployeeDto> listOfEmployees;
    public ObservableCollection<EmployeeDto> ListOfEmployees
    {
        get { return listOfEmployees; }
        set
        {
            if (listOfEmployees != value)
            {
                listOfEmployees = value;
                NotifyPropertyChanged("ListOfEmployee");
            }
        }
    }

    private EmployeeDto selectedEmployee;
    public EmployeeDto SelectedEmployee
    {
        get { return selectedEmployee; }
        set
        {
            if (selectedEmployee != value)
            {
                selectedEmployee = value;
                NotifyPropertyChanged("SelectedEmployee");
            }
        }
    }

    #endregion

    #region UI control references

    /// <summary>
    /// search text property
    /// </summary>
    private string searchText;
    public string SearchText
    {
        get { return searchText; }
        set
        {
            if (searchText != value)
            {
                searchText = value;
                NotifyPropertyChanged("SearchText");
            }
        }
    }

    public string Location { get; set; }

    #endregion

    #region Relay Commands

    /// <summary>
    /// new command
    /// </summary>
    private ViewCommand newCommand;
    public ViewCommand NewCommand
    {
        get
        {
            if (newCommand == null)
                newCommand = new ViewCommand(param => this.NewEmployee());
            return newCommand;
        }
    }
    private void NewEmployee()
    {
        NavigationActions.NewEmployeeView();
    }

    /// <summary>
    /// edit command
    /// </summary>
    private ViewCommand editCommand;
    public ViewCommand EditCommand
    {
        get
        {
            if (editCommand == null)
            {
                editCommand = new ViewCommand(param => this.EditEmployee());
            }
            return editCommand;
        }
    }

    private void EditEmployee()
    {
        NavigationActions.OpenEmployeeView(SelectedEmployee);
    }

    /// <summary>
    /// save command
    /// </summary>
    private ViewCommand saveCommand;
    public ViewCommand SaveCommand
    {
        get
        {
            if (saveCommand == null)
            {
                saveCommand = new ViewCommand(
                        param => this.SaveEmployee(),
                        param => this.CanSaveEmployee
                        );
            }
            return saveCommand;
        }
    }

    public void SaveEmployee()
    {
        employeeRpository.SaveChanges();
    }

    private bool CanSaveEmployee
    {
        get { return true; }
    }

    /// <summary>
    /// clear search command
    /// </summary>
    private ViewCommand clearSearchCommand;
    public ViewCommand ClearSearchCommand
    {
        get
        {
            if (clearSearchCommand == null)
                clearSearchCommand = new ViewCommand(param => this.ClearSearch());
            return clearSearchCommand;
        }
    }

    private void ClearSearch()
    {
        this.SearchText = string.Empty;
        ListOfEmployees = new ObservableCollection<EmployeeDto>(employeeRpository.GetEmployees(true));
    }

    /// <summary>
    /// search command
    /// </summary>
    private ViewCommand searchCommand;
    public ViewCommand SearchCommand
    {
        get
        {
            if (searchCommand == null)
                searchCommand = new ViewCommand(param => this.SearchEmployee());
            return searchCommand;
        }
    }

    private void SearchEmployee()
    {
        if (this.SearchText == string.Empty || this.SearchText == null)
        {
            NavigationActions.ShowError("Search Employees.", "Please enter your search text ...");
            return;
        }
        ListOfEmployees = new ObservableCollection<EmployeeDto>(employeeRpository.GetEmployeesByQuery(SearchText, Location));
    }

    /// <summary>
    /// exit command
    /// </summary>
    private ViewCommand exitCommand;
    public ViewCommand ExitCommand
    {
        get
        {
            if (exitCommand == null)
            {
                exitCommand = new ViewCommand(param => this.ExitWindow());
            }
            return exitCommand;
        }
    }

    private void ExitWindow()
    {
        NavigationActions.CloseCurrentView();
    }
    #endregion


    #region INotifyPropertyChanged Members

    public event PropertyChangedEventHandler PropertyChanged;

    public void NotifyPropertyChanged(String info)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(info));
        }
    }

    #endregion
    }
}

<Window x:Class="Attendance.Views.EmployeeSelectView"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:vm="clr-namespace:Attendance.ViewModels"
    Title="Employee Maintenance" FocusManager.FocusedElement="{Binding ElementName=txtSearchCriteria}"
    Height="525" Width="800" WindowStartupLocation="CenterScreen" WindowState="Normal"
    WindowStyle="SingleBorderWindow" Icon="Images/gb_icon.png">
<Window.DataContext>
    <vm:EmployeeSelectViewModel />
</Window.DataContext>
<Window.Resources>
    <ResourceDictionary>
        <ResourceDictionary.MergedDictionaries>
            <ResourceDictionary Source="Themes/DataGrid.Generic.xaml" />
        </ResourceDictionary.MergedDictionaries>
        <!--xml data start-->
        <XmlDataProvider x:Key="LocationData" XPath="LocationList/LocationItem" Source="XMLData/Location.xml"/>
        <!--xml data end-->
    </ResourceDictionary>
</Window.Resources>
<Grid Width="775">
    <DockPanel HorizontalAlignment="Left" Width="770">
        <!-- TOOLBAR -->
        <DockPanel DockPanel.Dock="Top" MinHeight="30" Margin="5">
            <ToolBar FontWeight="Bold">
                <!-- NEW -->
                <Button Name="btnNew" Command="{Binding Path=NewCommand}">
                    <Button.ToolTip>
                        <StackPanel>
                            <Label FontWeight="Bold" Background="SteelBlue" Foreground="White">
                                Create a new Customer
                            </Label>
                            <TextBlock Padding="10" TextWrapping="WrapWithOverflow" Width="200">
                            Create a new customer in a new Window tab.
                            </TextBlock>
                            <Line Stroke="SteelBlue" StrokeThickness="1" X2="200" />
                            <StackPanel Orientation="Horizontal">
                                <Image Margin="2" Source="Images/new.png"/>
                                <Label>Press F1 for more help</Label>
                            </StackPanel>
                        </StackPanel>
                    </Button.ToolTip>
                    <StackPanel Orientation="Horizontal">
                        <Image Source="Images/new.png" Width="22" Height="22" Margin="2"/>
                        <Label VerticalAlignment="Center">_New</Label>
                    </StackPanel>
                </Button>
                <!-- EDIT -->
                <Button Name="btnEdit" Command="{Binding Path=EditCommand}">
                    <Button.ToolTip>
                        <StackPanel>
                            <Label FontWeight="Bold" Background="SteelBlue" Foreground="White">
                                Edit the current record
                            </Label>
                            <TextBlock Padding="10" TextWrapping="WrapWithOverflow" Width="200">
                            Edit the current selected Customer.
                            </TextBlock>
                            <Line Stroke="SteelBlue" StrokeThickness="1" X2="200" />
                            <StackPanel Orientation="Horizontal">
                                <Image Margin="2" Source="Images/dialog-information.png"/>
                                <Label>Press F1 for more help</Label>
                            </StackPanel>
                        </StackPanel>
                    </Button.ToolTip>

                    <StackPanel Orientation="Horizontal">
                        <Image Source="Images/edit.png" Width="22" Height="22" Margin="2" />
                        <Label VerticalAlignment="Center">_Edit</Label>
                    </StackPanel>
                </Button>
                <!-- SEARCH -->
                <Separator />
                <TextBox Name="txtSearchCriteria" 
                    MinWidth="300" Margin="5"
                    BorderThickness="1" BorderBrush="LightGray"
                    FontWeight="Normal" Foreground="Gray" Text="{Binding Path=SearchText}">
                </TextBox>
                <Button Name="btnSearch" Command="{Binding Path=SearchCommand}">
                    <Button.ToolTip>
                        <StackPanel>
                            <Label FontWeight="Bold" Background="SteelBlue" Foreground="White">
                                Search
                            </Label>
                            <TextBlock Padding="10" TextWrapping="WrapWithOverflow" Width="200">
                            Search a specific Customer.
                            </TextBlock>
                            <Line Stroke="SteelBlue" StrokeThickness="1" X2="200" />
                            <StackPanel Orientation="Horizontal">
                                <Image Margin="2" Source="Images/find.png"/>
                                <Label>Press F1 for more help</Label>
                            </StackPanel>
                        </StackPanel>
                    </Button.ToolTip>
                    <StackPanel Orientation="Horizontal">
                        <Image Source="Images/find.png" Width="22" Height="22" Margin="2" />
                        <Label VerticalAlignment="Center">_Find</Label>
                    </StackPanel>
                </Button>
                <Button Name="btnClearSearch" Command="{Binding Path=ClearSearchCommand}">
                    <Button.ToolTip>
                        <StackPanel>
                            <Label FontWeight="Bold" Background="SteelBlue" Foreground="White">
                                Search
                            </Label>
                            <TextBlock Padding="10" TextWrapping="WrapWithOverflow" Width="200">
                            Clear search results.
                            </TextBlock>
                            <Line Stroke="SteelBlue" StrokeThickness="1" X2="200" />
                            <StackPanel Orientation="Horizontal">
                                <Image Margin="2" Source="Images/find.png"/>
                                <Label>Press F1 for more help</Label>
                            </StackPanel>
                        </StackPanel>
                    </Button.ToolTip>
                    <StackPanel Orientation="Horizontal">
                        <Label VerticalAlignment="Center">_Clear Search</Label>
                    </StackPanel>
                </Button>
                <!-- EXIT -->
                <Separator />
                <Button Name="btnExit" Command="{Binding Path=ExitCommand}">
                    <Button.ToolTip>
                        <StackPanel>
                            <Label FontWeight="Bold" Background="SteelBlue" Foreground="White">
                            开发者_Go百科    Start the application
                            </Label>
                            <TextBlock Padding="10" TextWrapping="WrapWithOverflow" Width="200">
                            Start the main application with the M-V-MV pattern.
                            </TextBlock>
                            <Line Stroke="SteelBlue" StrokeThickness="1" X2="200" />
                            <StackPanel Orientation="Horizontal">
                                <Image Margin="2" Source="Images/dialog-information.png"/>
                                <Label>Press F1 for more help</Label>
                            </StackPanel>
                        </StackPanel>
                    </Button.ToolTip>

                    <StackPanel Orientation="Horizontal">
                        <Image Source="Images/exit.png" Width="22" Height="22" Margin="2" />
                        <Label VerticalAlignment="Center">_Exit</Label>
                    </StackPanel>
                </Button>
            </ToolBar>
        </DockPanel>
        <!-- LIST -->
        <DockPanel DockPanel.Dock="Top" MinHeight="30" Margin="0,0,0,5">
            <Label>Location:</Label>
            <ComboBox Name="cboLocation" Grid.Column="1" Grid.Row="4" 
                                ItemsSource="{Binding Source={StaticResource LocationData}}"
                                DisplayMemberPath="location_text" SelectedValuePath="location_value" 
                                SelectedValue="{Binding Path=Location}" 
                                HorizontalAlignment="Left" Width="175" Margin="4" />
        </DockPanel>
        <DockPanel Margin="5">
            <DataGrid ItemsSource="{Binding Path=ListOfEmployees}" AutoGenerateColumns="False" IsReadOnly="True" 
                Name="dgEmployee" SelectionMode="Single" SelectionUnit="FullRow" CanUserResizeColumns="True" 
                SelectedItem="{Binding Path=SelectedEmployee}" GridLinesVisibility="Horizontal">
                <DataGrid.Columns>
                    <DataGridTextColumn Header="Employee ID" Width="SizeToCells"  MinWidth="125" Binding="{Binding EmployeeID}" />
                    <DataGridTextColumn Header="First Name" Width="SizeToCells"  MinWidth="200" Binding="{Binding FirstName}" />
                    <DataGridTextColumn Header="Last Name" Width="SizeToCells"  MinWidth="200" Binding="{Binding LastName}" />
                    <DataGridTextColumn Header="Location" Width="SizeToCells"  MinWidth="125" Binding="{Binding Location}" />
                    <DataGridCheckBoxColumn x:Name="Active" Header="Active" Binding="{Binding active}" MinWidth="75" />
                </DataGrid.Columns>
            </DataGrid>
        </DockPanel>
    </DockPanel>
</Grid>

This was my solution:

<DataGrid Name="dgrid" ItemsSource="{Binding UserSettings, IsAsync=True}" AutoGenerateColumns="False">

The key being the setting of IsAsync=True, allows the screen paint to occur

I found 2 ways to refresh DataGrid:

1. One was posted by VariableLost, it works with INotifyPropertyChanged but have one drawback. Whole DataGrid is refreshed with blink effect (disappears for a split second). Doesn't look natural.
2. Other solution is to refresh ObservableCollection in ViewModel or Code Behind (if you're not using MVVM):

CollectionViewSource.GetDefaultView(collectionName).Refresh();

Looks more natural because only changes cells affected by edition.

Your previous code should have also worked, but 'magic strings' got in the way. Property name is ListOfEmployees and in its setter you raise PropertyChanged event with property name ListOfEmployee. 's' is missing.

Beware of your new code. It will raise CollectionChanged event on ListOfEmployees for every insertion, and that might make your app slower if you are doing many insertions. For many insertions, it would be better to derive from ObservableCollection and implement Reset method that clears underlying Items, adds new items and raises CollectionChanged event of type Reset.

My question was answered in a post on another site. Instead of creating a new instance of the ListOfEmployees in my view model, I just cleared the existing one and added the results from my repository:

        private void SearchEmployee()
    {
        if (String.IsNullOrEmpty(this.SearchText) || String.IsNullOrEmpty(this.Location))
        {
            NavigationActions.ShowError("Search Employees.", "Please enter your search text and select a location...");
            return;
        }

        // clear the list and repopulate based on the search criteria
        if (ListOfEmployees != null)
        {
            ListOfEmployees.Clear();

            IList<EmployeeDto> iList = employeeRpository.GetEmployeesByQuery(SearchText, Location, IsActive);
            foreach (EmployeeDto value in iList)
                ListOfEmployees.Add(value);
        }
    }

That did the trick.