PanelBackend

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Media;

namespace Connect4
{
    class PanelBackend
    {
        public SolidColorBrush[,] panel;

        public PanelBackend()
        {
            panel = new SolidColorBrush[6, 7];
        }

        public int DropDisk(int? currentMove, SolidColorBrush diskColor)
        {
            int slot = currentMove ?? default(int);
            int height = GetHeight(slot);
            panel[height, slot] = diskColor;

            return height;
        }

        public bool CheckForWin(int height, int slot)
        {
            return (CheckDiagonal(height, slot)
                || CheckHorizontal(height, slot)
                || CheckVertical(height, slot));
        }

        private bool CheckDiagonal(int height, int slot)
        {
            int count = 0;
            int reverseCount = 0;
            int tempHeight = height;

            // count from all four lines going diagonally away from the current move
            // counts up and to the right 
            for (int tempSlot = slot; (tempSlot < panel.GetLength(1) && tempHeight < panel.GetLength(0)); tempSlot++)
            {
                if (panel[tempHeight, tempSlot] == panel[height, slot])
                {
                    count += 1;
                }
                else
                { break; }

                tempHeight += 1;
            }
            tempHeight = height;
            if (count == 4)
                return true;

            // counts down and to the left to join the first partial line with this one
            for (int tempSlot = slot; (tempSlot > 0 && tempHeight > 0); tempSlot++)
            {
                if (panel[tempHeight, tempSlot] == panel[height, slot])
                {   // don't count the origin again
                    if (tempSlot != slot && tempHeight != height)
                        count += 1;
                }
                else { break; }

                tempHeight -= 1;
            }
            if (count == 4)
                return true;
            tempHeight = height;

            // counts up and to the left
            for (int tempSlot = slot; (tempSlot > 0 && tempHeight < panel.GetLength(0)); tempSlot--)
            {
                if (panel[tempHeight, tempSlot] == panel[height, slot])
                {
                    reverseCount += 1;
                }
                else { break; }

                tempHeight += 1;
            }
            tempHeight = height;

            // counts down and to the right to finish the up and to the left line
            for (int tempSlot = slot; (tempSlot < panel.GetLength(1) && tempHeight > 0); tempSlot++)
            {
                if (panel[tempHeight, tempSlot] == panel[height, slot])
                {   // don't count the origin again
                    if (tempSlot != slot && tempHeight != height)
                        reverseCount += 1;
                }
                else { break; }

                tempHeight -= 1;
            }
            if (reverseCount == 4)
                return true;

            return (count >= 4 || reverseCount >= 4);
        }

        private bool CheckHorizontal(int height, int slot)
        {
            int count = 0;
            for (int col = 0; col < panel.GetLength(1); col++)
            {
                if (panel[height, col] == panel[height, slot])
                {
                    if ((count += 1) == 4)
                        break;
                }
                else
                    count = 0;
            }

            return count == 4;
        }

        private bool CheckVertical(int height, int slot)
        {
            int count = 0;
            for (int row = 0; row < panel.GetLength(0); row++)
            {
                if (panel[row, slot] == panel[height, slot])
                {
                    if ((count += 1) == 4)
                        break;
                }
                else
                    count = 0;
            }

            return count == 4;
        }

        public int GetHeight(int slot)
        {
            int number = 6;

            for (int lastFilledRow = 0; lastFilledRow < 5; ++lastFilledRow)
            {
                if (panel[lastFilledRow, slot] == null)
                {
                    number = lastFilledRow;
                }
                else
                    break;
            }

            return number;
        }
    }
}

xaml

<Window x:Class="Connect4.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:Connect4"
        mc:Ignorable="d"
        Title="Connect 4" Height="350" Width="525">
        <!-- contains and organizes the game area and reset button -->
        <Grid x:Name="BaseOrganizer" Background="Black">
        <!--
            top grid row = top row that placeholder disk moves in
            middle six grid rows = game area 
            bottom grid row = reset button 
        -->
        <Grid.RowDefinitions>
            <RowDefinition Height="*"/>
            <RowDefinition Height="6*"/>
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>
        <!-- where the action happens -->
        <Grid x:Name="gamePanel"
                  Grid.Row="1" 
                  Grid.Column="0"
                  Grid.ColumnSpan="7"
                  Background="Blue"
                  ShowGridLines="True">
                <Canvas x:Name="animationBoard" />
            </Grid>
        <!-- user controls -->
        <DockPanel x:Name="UserControlls" Grid.Row="2" >
            <Button x:Name="resetButton"  
                    Content="Reset the game" 
                    Click="resetButton_Click">
                <Button.Background>
                    <LinearGradientBrush>
                        <LinearGradientBrush.GradientStops>
                            <GradientStop Offset="0.0" Color="Red" />
                            <GradientStop Offset="1.0" Color="Blue" />
                        </LinearGradientBrush.GradientStops>
                    </LinearGradientBrush>
                </Button.Background>
            </Button>
        </DockPanel>
    </Grid>
</Window>

xaml.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Windows.Threading;

namespace Connect4
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        private DispatcherTimer timer = new DispatcherTimer();
        private int startTop = 80;
        private int currentTop;
        private int bottom = 330;
        private SolidColorBrush yellow = Brushes.Yellow;
        private SolidColorBrush red = Brushes.Red;
        private SolidColorBrush turn;
        private PanelBackend panel;
        private int[] XY = new int[2];
        private int animationStopRow;
        private Ellipse currentEllipse;

        public MainWindow()
        {
            InitializeComponent();
            SetUpGamePanel();
            Play();
        }

        public void Play()
        {
            int turnCounter = 0;


            do
            {
                turn = ((turnCounter += 1) % 2 == 0) 
                    ? red 
                    : yellow;

                Ellipse disk = Disk(turn);
                currentEllipse = disk;
                Keyboard.Focus(disk);                
            }
            while (!IsWinningMove() && turnCounter < 42);

            if (turnCounter < 42)
                FlashingHappyFunTime();
            else
                Reset();

            panel = new PanelBackend();
        }

        private int[] GetMove(Ellipse currentDisk)
        {
            int lastCol = XY[1];
            int currentCol = lastCol;
            while (currentCol == lastCol)
            {
                currentCol = lastCol + 1;
            }
            
            return XY;
        }

        private bool IsWinningMove()
        {
            SolidColorBrush b = Brushes.Yellow;
            animationStopRow = panel.DropDisk(XY[1], ((SolidColorBrush)currentEllipse.Fill));

            return panel.CheckForWin(animationStopRow, XY[1]);
        }

        private void InitTimer()
        {
            timer.Interval = new TimeSpan(0, 0, 0, 0, 25);
            timer.Tick += AnimateDiskDrop;
        }

        private void AnimateDiskDrop(object sender, EventArgs e)
        {
            const int updateDistance = 10;
            if (currentTop + updateDistance <= bottom)
            {
                currentTop += updateDistance;
                Canvas.SetTop(Disk(Brushes.Yellow), currentTop);
            }
            else
            {
                timer.Stop();
            }
        }

        private void FlashingHappyFunTime()
        {
            //throw new NotImplementedException();
        }
        
        private Grid SetUpGamePanel()
        {
            panel = new PanelBackend();
            gamePanel.ColumnDefinitions.Add(Col());
            for (int row = 0; row < 6; row++)
            {
                gamePanel.RowDefinitions.Add(Row());
                gamePanel.ColumnDefinitions.Add(Col());
            }

            return gamePanel;
        }

        private Ellipse Disk(SolidColorBrush turn)
        {
            const int size = 30;
            Ellipse disk = new Ellipse();
            disk.Fill = turn;
            disk.Width = disk.Height = size;
            disk.KeyDown += Disk_KeyDown;

            return disk;
        }

        private void Disk_KeyDown(object sender, KeyEventArgs e)
        {
            while (e.Key != Key.Enter)
            {
                if (e.Key == Key.Right)
                {
                    // cd.location -= UpdateDistance;
                }
                else if (e.Key == Key.Left)
                {
                    // cd.location += updateDistance;
                }
            }

            // XY[0] = cd.location;
           int current = XY[1];
           //var currentPosition = sender.TranslatePoint(new Point(0, 0), gamePanel);
        }

        private RowDefinition Row()
        {
            return new RowDefinition();
        }

        private ColumnDefinition Col()
        {
            return new ColumnDefinition();
        }

        private void resetButton_Click(object sender, RoutedEventArgs e)
        {
            Reset();
        }

        private void Reset()
        {
            //SetUpGamePanel();
        }
    }
}