Click Event Not Firing After Changing ObservableCollection

Question

I am not experienced with WPF, so please forgive my lack of understanding.

EDIT: I'm working on a simplistic chess GUI, and the pieces move fine until one tries to move a piece that has already been moved. If we try to move the piece to a previously occupied square, the click event won't fire at all. If we try to move it to a previously untouched square, the event will fire, but the UI won't update.

Here's the XAML for the chessboard (borrowed from here: WPF controls needed to build chess application ):

<Window x:Class="Client.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:Client"
        xmlns:defaults="clr-namespace:butnotquite.Defaults;assembly=butnotquite"
        mc:Ignorable="d" 
        Title="butnotquite Chess" Height="600" Width="600">

    <Window.Resources>
        <DrawingBrush x:Key="Checkerboard" Stretch="None" TileMode="Tile" Viewport="0,0,2,2" ViewportUnits="Absolute">
            <DrawingBrush.Drawing>
                <DrawingGroup>
                    <GeometryDrawing Brush="Tan">
                        <GeometryDrawing.Geometry>
                            <RectangleGeometry Rect="0,0,2,2" />
                        </GeometryDrawing.Geometry>
                    </GeometryDrawing>
                    <GeometryDrawing Brush="Brown">
                        <GeometryDrawing.Geometry>
                            <GeometryGroup>
                                <RectangleGeometry Rect="0,0,1,1" />
                                <RectangleGeometry Rect="1,1,1,1" />
                            </GeometryGroup>
                        </GeometryDrawing.Geometry>
                    </GeometryDrawing>
                </DrawingGroup>
            </DrawingBrush.Drawing>
        </DrawingBrush>

        <Style x:Key="PieceStyle" TargetType="{x:Type Image}">
            <Style.Triggers>
                <MultiDataTrigger>
                <MultiDataTrigger.Conditions>
                    <Condition Binding="{Binding PieceType}" Value="{x:Static defaults:PieceType.None}"/>
                    <Condition Binding="{Binding Color}" Value="{x:Static defaults:Color.None}"/>
                </MultiDataTrigger.Conditions>
                <MultiDataTrigger.Setters>
                    <Setter Property="Image.Source" Value="/Images/empty_square.png" />
                </MultiDataTrigger.Setters>
            </MultiDataTrigger>
            <MultiDataTrigger>
                <MultiDataTrigger.Conditions>
                    <Condition Binding="{Binding PieceType}" Value="{x:Static defaults:PieceType.Pawn}"/>
                    <Condition Binding="{Binding Color}" Value="{x:Static defaults:Color.White}"/>
                </MultiDataTrigger.Conditions>
                <MultiDataTrigger.Setters>
                    <Setter Property="Image.Source" Value="/Images/white_pawn.png" />
                </MultiDataTrigger.Setters>
            </MultiDataTrigger>             
            </Style.Triggers>
        </Style>
    </Window.Resources>

    <Viewbox>
        <ItemsControl Name="ChessboardUI">
            <ItemsControl.ItemsPanel>
                <ItemsPanelTemplate>
                    <Canvas Width="8" Height="8" Background="{StaticResource Checkerboard}"/>
                </ItemsPanelTemplate>
            </ItemsControl.ItemsPanel>
            <ItemsControl.ItemTemplate>
                <DataTemplate>
                    <Border Name="square"  PreviewMouseDown="square_MouseLeftButtonDown" Width="1" Height="1" >
                        <Image Width="0.8" Height="0.8" Style="{StaticResource PieceStyle}"/>
                    </Border>
                </DataTemplate>
            </ItemsControl.ItemTemplate>
            <ItemsControl.ItemContainerStyle>
                <Style>
                    <Setter Property="Canvas.Left" Value="{Binding Position.X}" />
                    <Setter Property="Canvas.Top" Value="{Binding Position.Y}" />
                </Style>
            </ItemsControl.ItemContainerStyle>
        </ItemsControl>
    </Viewbox>
</Window>

I've ommitted the multidata triggers for all pieces as they are all similar.

Here's the viewmodel. I'm using the MVVMLight library:

public class PieceViewModel : ViewModelBase
{
    private PieceType pieceType;
    private Color color;
    private Point position;

    public PieceType PieceType
    {
        get
        {
            return this.pieceType;
        }

        set
        {
            this.pieceType = value;
            base.RaisePropertyChanged(() => this.PieceType);
        }
    }

    public Color Color
    {
        get
        {
            return this.color;
        }

        set
        {
            this.color = value;
            base.RaisePropertyChanged(() => this.Color);
        }
    }

    public Point Position
    {
        get
        {
            return this.position;
        }

        set
        {
            this.position = value;
            base.RaisePropertyChanged(() => this.Position);
        }
    }
}

Here's how I fill the ObservableCollection:

private void BindPieces()
    {
        this.chessboard = new Chessboard(false);
        this.pieces = new ObservableCollection<PieceViewModel>();

        for (int square = 0; square < this.chessboard.Board.Length; square++)
        {
            int x = square % 8;
            int y = square / 8;
            Point position = new Point(x, y);
            PieceViewModel pieceModel = new PieceViewModel()
            {
                PieceType = this.chessboard.Board[square].OccupiedBy.Type,
                Color = this.chessboard.Board[square].OccupiedBy.Color,
                Position = position
            };

            this.pieces.Add(pieceModel);
        }

        this.ChessboardUI.ItemsSource = this.pieces;
    }

More code can be found here: https://github.com/YouJinTou/butnotquite/tree/master/Client

Thanks for any and all help.

Answer 1

As lokusking has commented, the collection needs to be instantiated only once, which was the case here; however, I had failed to clear it and rebind it after every click. It seems like a hackish solution, but it works.