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    <Grid Name="myGrid">
                <Grid Background="#FFE5E5E5">
                    <StackPanel HorizontalAlignment="Left" Height="35" Margin="2,2,0,0" VerticalAlignment="Top" Orientation="Horizontal">
                        <TextBlock Margin="0,4" FontSize="20" Text="Buchnummer"/>
                        <Button x:Name="btnABBUCH" Margin="4,0,0,0" Width="60" Content="{Binding Path=ABBUCH}" Click="btnABBUCH_Click" Template="{DynamicResource ButtonTemplateBuchnummer}" Style="{StaticResource ButtonBuchnummerStyle}"/>
                    </StackPanel>
               </Grid>
    </Grid>					

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namespace Buchnummer
{
    public partial class MainWindow : Window
    {

        private dsBuchnummer myBuchnummer = new dsBuchnummer();

        public MainWindow()
        {
            InitializeComponent();
            prcBuchnummer();
        }

        private void Confirm_Executed(object sender, ExecutedRoutedEventArgs e)
        {
            myBuchnummer = new dsBuchnummer();
            myGrid.DataContext = myBuchnummer;
            e.Handled = true;
        }

        private void prcBuchnummer()
        {
                myGrid.DataContext = myBuchnummer;
                myBuchnummer.ABBUCH = "123";
            }
        }

        //Vergabe der nächsten Buchnummer
        private void btnABBUCH_Click(object sender, RoutedEventArgs e)
        {
            myBuchnummer.ABBUCH = "12345";
        }
    }

    public class dsBuchnummer : IDataErrorInfo
    {
        public string ABBUCH { get; set; }

        public string Error
        {
            get { throw new NotImplementedException(); }
        }

        public string this[string columnName]
        {
            get
            {
                string result = null;
                int intNummer = 0;

                if (columnName == "ABBUCH")
                {
                }

                else if (1==1)
                {
                }

                return result;
            }
        }
    }
}