UserControl.xaml:

<UserControl x:Class="TextBoxForUserControl.UserControl1"
             d:DesignHeight="{Binding ElementName=sp,Path=Height}" d:DesignWidth="{Binding ElementName=sp,Path=Width}">

    <StackPanel Orientation="Horizontal" Background="LightGray" x:Name="sp"  >
        <TextBox x:Name="tb" Height="40" DataContext="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType=UserControl}}"   Text="{Binding Item}"  Background="Transparent" />
        <Button x:Name="del" Content="×"   Background="Transparent" FontWeight="Bold" FontSize="30" Foreground="HotPink" >
            <Button.Style>
                <Style TargetType="Button">
                    <Setter Property="Template">
                        <Setter.Value>
                            <ControlTemplate TargetType="Button">
                                <Grid>
                                    <ContentPresenter HorizontalAlignment="Center"
                            VerticalAlignment="Center"/>
                                </Grid>
                            </ControlTemplate>
                        </Setter.Value>
                    </Setter>
                </Style>
            </Button.Style>
        </Button>

    </StackPanel>
</UserControl>

UserControl.xaml.cs:

public partial class UserControl1 : UserControl
  {
    public UserControl1()
    {
      InitializeComponent();
   
    }
    public string Item
    {
      get { return (string)GetValue(ItemProperty);}
      set { SetValue(ItemProperty,value);}
    }
    public static readonly DependencyProperty ItemProperty=
      DependencyProperty.Register("Item",typeof(string),typeof(UserControl1),new PropertyMetadata("Unspecified"));

   
  }
MainWindow.xaml:

<StackPanel>
        <StackPanel Orientation="Horizontal">
            <TextBox x:Name="input" Width="300" Height="40" Background="AliceBlue" Text="{Binding MyItem,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"  />
            <Button x:Name="add" Content="Add" Width="80" Height="40"  Background="LightBlue" Click="add_Click" />
        </StackPanel>
        <WrapPanel  Name="panel">
        </WrapPanel>
    </StackPanel>
MainWindow.xaml.cs:
public partial class MainWindow : Window
  {
    UserControl1 uc =null;
    ViewModel vm=new ViewModel();
    public MainWindow()
    {
      InitializeComponent();
      DataContext=vm;
    }
   
    private void add_Click(object sender, RoutedEventArgs e)
    {
      uc = new UserControl1();
      uc.Item=vm.MyItem;
      panel.Children.Add(uc);
   
    }
  }
  public class ViewModel:INotifyPropertyChanged
  {
   
    private string myItem;

    public string MyItem
    {
      get { return myItem; }
      set
      {
        myItem = value;
        OnPropertyChanged("MyItem");
      }
    }

    public event PropertyChangedEventHandler PropertyChanged;
    protected virtual void OnPropertyChanged(string name)
    {
      var handler = System.Threading.Interlocked.CompareExchange(ref PropertyChanged, null, null);
      if (handler != null)
      {
        handler(this, new PropertyChangedEventArgs(name));
      }
    }
  }