バインディングオブジェクト内の変更をコントロールに反映するには

public event System.ComponentModel.PropertyChangedEventHandler PropertyChanged;

protected void OnPropertyChanged(string name)
{
    if (PropertyChanged != null)
    {
        PropertyChanged(this, new System.ComponentModel.PropertyChangedEventArgs(name));
    }
}

private string _userId;
public string UserId
{
    get
    {
        return _userId;
    }
    set
    {
        _userId = value; 
        OnPropertyChanged("UserId");
    }
}

public class TopLevel : System.ComponentModel.INotifyPropertyChanged
{
    private string _userId;
    public string UserId
    {
        get
        {
            return _userId;
        }
        set
        {
            _userId = value; 
            OnPropertyChanged("UserId");
        }
    }

    public ObservableCollection<SecondLevel> SecondLevels { get; set; } }
    
    #region INotifyPropertyChanged メンバー

    public event System.ComponentModel.PropertyChangedEventHandler PropertyChanged;
    
    protected void OnPropertyChanged(string name)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new System.ComponentModel.PropertyChangedEventArgs(name));
        }
    }

    #endregion
}