// MyView.xaml.cs
    public partial class MyView : UserControl, IViewFor<MyViewModel>
    {
        public MyView()
        {
            InitializeComponent();
            ViewModel = new MyViewModel();
            _otherViewModel = new MyViewModel();
            this.Bind(_otherViewModel, vm => vm.StrProp, v => v.textBox.Text);
        }

        private readonly MyViewModel _otherViewModel;

        public static readonly DependencyProperty ViewModelProperty = DependencyProperty.Register(
            "ViewModel", typeof (MyViewModel), typeof (MyView), new PropertyMetadata(default(MyViewModel)));


        public MyViewModel ViewModel
        {
            get { return (MyViewModel) GetValue(ViewModelProperty); }
            set { SetValue(ViewModelProperty, value); }
        }

        object IViewFor.ViewModel
        {
            get { return ViewModel; }
            set { ViewModel = (MyViewModel) value; }
        }

        private void ButtonBase_OnClick(object sender, RoutedEventArgs e)
        {
            MessageBox.Show("ViewModel.StrProp = " + ViewModel.StrProp +
                "\nOtherViewModel.StrProp = " + _otherViewModel.StrProp);
        }
    }

    public class MyViewModel : ReactiveObject
    {
        private string _strProp;
        public string StrProp
        {
            get { return _strProp; }
            set { this.RaiseAndSetIfChanged(ref _strProp, value); }
        }
    }

// MyView.xaml
<UserControl x:Class="WpfApplication1.MyView"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             mc:Ignorable="d"
             d:DesignHeight="300" d:DesignWidth="300">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition />
            <RowDefinition />
        </Grid.RowDefinitions>
        <TextBox x:Name="textBox"></TextBox>
        <Button Grid.Row="1" Click="ButtonBase_OnClick">Show ViewModel and OtherViewModel</Button>
    </Grid>
</UserControl>