C#

    <Window.Resources>
        <c:CMyData x:Key="mObj" pText="George"/>
    </Window.Resources>
    
    
    <DockPanel Name="dockPanel1">
        <Border BorderBrush="Silver" BorderThickness="1" Name="border1" DockPanel.Dock="Top" HorizontalAlignment="Stretch" VerticalAlignment="Top" Height="50">
            <Button Content="Button" Name="button1" Height="47" Click="button1_Click" />
        </Border>
        <Border BorderBrush="Silver" BorderThickness="1" Name="border2">
            <TextBox>
                <TextBox.Text>
                    <Binding Source="{StaticResource mObj}" Path="pText" UpdateSourceTrigger="PropertyChanged" Mode="TwoWay" />
                </TextBox.Text>
            </TextBox>    
        </Border>
    </DockPanel>
</Window>

public class CMyData     : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;
        
        
        private string text="";

        public string pText
        {
            get { return text; }
            set 
            { 
                text = value;
                OnPropertyChanged("CHANGED");
            }
        }

       
        protected void OnPropertyChanged(string name)
        {
            PropertyChangedEventHandler handler = PropertyChanged;
 
            if (handler != null) 
            {
                handler(this, new PropertyChangedEventArgs(name));
            }
        }


    }

    public partial class MainWindow : Window
    {
        public CMyData mObj;
        
        
        public MainWindow()
        {
            InitializeComponent();
            mObj = new CMyData();
        }

        private void textBox1_TextChanged(object sender, TextChangedEventArgs e)
        {

        }

        private void button1_Click(object sender, RoutedEventArgs e)
        {
            mObj.pText = "Hello\r\nWorld";
           // UpdateLayout();
        }
    }