How do I fix this problem?

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C#

SQL

WPF

Hi people! I am pretty new in all this. And I don't have so much time because of my little baby. I appreciate any help I can get.
Here is the code.
XAML:

<window x:class="Aukcija1.MainWindow" xmlns:x="#unknown">
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="Auctions" Height="350" Width="525">
    xmlns:wf="clr-namespace:System.Windows.Forms;assembly=System.Windows.Forms"> 
    
    <grid>
DataContext="{Binding}">
        <datagrid> AutoGeneratedColumns="False" EnableRowVirtualization="True" Height="264" HorizontalAlignment="Left" ItemsSource="{Binding}" Name="aukcija_bazeDataGrid" RowDetailsVisibilityMode="VisibleWhenSelected" VerticalAlignment="Top" Width="503" SelectionChanged="aukcija_bazeDataGrid_SelectionChanged" >
            <datagrid.columns>
                <datagridtextcolumn x:name="aukcijaIDColumn" binding="{Binding Path=auction_ID}" header="Auction ID" width="SizeToHeader" />
                <datagridtextcolumn x:name="artikalNameColumn" binding="{Binding Path=item_name}" header="Item Name" width="SizeToHeader" />
                <datagridtextcolumn x:name="pocetnacijenaColumn" binding="{Binding Path=start_price}" header="Start Price" width="SizeToHeader" />
              <datagridtextcolumn x:name="trenutnacijenaColumn" binding="{Binding Path=current_price}" header="Current Price" width="SizeToHeader" />
            </datagrid.columns>
        </datagrid>
     <Button Content="Login" Height="23" HorizontalAlignment="Left" Margin="331,276,0,0" Name="button1" VerticalAlignment="Top" Width="75" Click="button1_Click" />
     <Button Content="New Auction" Height="23" HorizontalAlignment="Left" Margin="416,276,0,0" Name="button3" VerticalAlignment="Top" Width="75" Click="button3_Click" />
     <Button Content="Bid Price" Height="23" HorizontalAlignment="Left" Margin="12,276,0,0," Name="button2" VerticalAlignment="Top" Width="75" Click="button2_Click" />
    </grid>

</window>

C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
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.Data.SqlClient;
using System.Data;
using System.Windows.Threading;
using System.Windows.Forms;
using System.Timers;



namespace Aukcija1
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        DispatcherTimer timer;
        int interval;
        int step;

        public MainWindow()
        {
            interval = 1001;
            step = 20;
            timer = new DispatcherTimer();
            timer.Interval = TimeSpan.FromMilliseconds(interval);
            timer.Start();
            timer.Tick += new EventHandler(timer_Tick);

            DataTable AuctionsTable = new DataTable();
            SqlConnection conn = new SqlConnection(@"datasource=(local);database=Aukcija;integrated security=true;");
            SqlDataAdapter aukcDa = new SqlDataAdapter("select * from auctions", conn);

            aukcDa.Fill(AuctionsTable);
            aukcija_bazeDataGrid.DataContext = AuctionsTable;

        }

        private void InitializeComponent()
        {
            throw new NotImplementedException();
        }

        void timer_Tick(object sender, EventArgs e)
        {
            if (Canvas.GetLeft(button1) > 400)
                timer.Stop();
            step = (step > 1) ? (step -= 1) : 1;
            Canvas.SetLeft(button1, Canvas.GetLeft(button1) + step);
            if (interval > 1)
                timer.Interval = TimeSpan.FromMilliseconds(interval -= 100);
        }

        private void listBox1_SelectionChanged(object sender, SelectedCellsChangedEventArgs e)
        {
            using (SqlConnection conn = new SqlConnection())
            {
                conn.ConnectionString = (@"datasource=(local);database=Aukcija;integrated security=true;");
                SqlCommand command = conn.CreateCommand();
                command.CommandType = CommandType.StoredProcedure;
                command.CommandText = "uspPovecajCenuArtiklaZaJedan";
                command.Parameters.AddWithValue("@auction_ID", aukcija_bazeDataGrid.SelectedValue);
                conn.Open();
                command.ExecuteNonQuery();
            }

        }

        private void button1_Click(object sender, RoutedEventArgs e)
        {
            Form1 popup = new Form1();
            popup.ShowDialog();

            popup.Dispose();
        }

        private void button3_Click(object sender, RoutedEventArgs e)
        {
            Form2 popup = new Form2();
            popup.ShowDialog();

            popup.Dispose();
        }

        private void button2_Click(object sender, RoutedEventArgs e)
        {
            using (SqlConnection conn = new SqlConnection())
            {
                conn.ConnectionString = (@"datasource=(local);database=Aukcija;integrated secutiry=true;");

                SqlCommand command = conn.CreateCommand();
                command.CommandType = CommandType.StoredProcedure;
                command.CommandText = "uspPovecajCenuArtiklaZaJedan";
                command.Parameters.AddWithValue("@auction_ID", 1);
                conn.Open();
                command.ExecuteNonQuery();
            }
        }

        private void loadGrid()
        {
            SqlConnection con = new SqlConnection(@"datasource=(local);database=Aukcija;integrated secutiry=true;");
            SqlDataAdapter ad = new SqlDataAdapter();
            SqlCommand cmd = new SqlCommand();
            con.Open();
            string strQuery = "select * from Auctions";
            cmd.CommandText = strQuery;
            ad.SelectCommand = cmd;
            cmd.Connection = con;
            DataSet ds = new DataSet();
            ad.Fill(ds);
            aukcija_bazeDataGrid.DataContext = ds.Tables[0].DefaultView;
            con.Close();
        }

        private void aukcija_bazeDataGrid_SelectionChanged(object sender, SelectedCellsChangedEventArgs e)
        {

        }

        public UIElement button1 { get; set; }
    }
}

SQL table:

Auctions (auction_ID, item_name, start_price, current_price).

I got these errors:
The name 'aukcija_bazeDataGrid' does not exist in the current context
The object 'Window' already has a child and cannot add ''. 'Window' can accept only one child. The property 'Content' is set more than once.