How to Pass a Value From a Window to a UserControl in WPF

I want to pass a value from MainWindow into my UserControl! I passed a value to my UserControl and the UserControl showed me the value in a MessageBox, but it is not showing the value in a TextBox. Here is my code:

MainWindow(Passing Value To UserControl)

try
{
    GroupsItems abc = null;
    if (abc == null)
    {
        abc = new GroupsItems();
        abc.MyParent = this;
        abc.passedv(e.ToString(), this);

    }
}
catch (Exception ee)
{
    MessageBox.Show(ee.Message);
}

UserControl

public partial class GroupsItems : UserControl
{
    public MainWindow MyParent { get; set; }
    string idd = "";
    public GroupsItems()
    {
        InitializeComponent();
        data();
    }

    public void passedv(string id, MainWindow mp)
    {
        idd = id.ToString();
        MessageBox.Show(idd);
        data();
    }

    public void data()
    {
        if (idd!="")
        {
            MessageBox.Show(idd);
            texbox.Text = idd;
        }
    }
}

EDIT(using BINDING and INotifyProperty )

.....

   public GroupsItems()
      {
            InitializeComponent();
      }

    public void passedv()
    {
        textbox1.Text = Text;
    }

}

public class Groupitm : INotifyPropertyChanged
{

    private string _text = "";

    public string Text
    {
        get { return _text; }
        set
        {
            if (value != _text)
            {
                _text = value;
                NotifyPropertyChanged();
            }
        }
    }



    public event PropertyChangedEventHandler PropertyChanged;

    protected void NotifyPropertyChanged(String propertyName = "")
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }