<Window x:Class="MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:MyApp"
        xmlns:vm="clr-namespace:MyApp.MainViewModelNameSpace"
        mc:Ignorable="d"
        Height="auto" Width="auto" WindowState="Maximized">
    <Window.DataContext >
        <vm:MainViewModel/>
    </Window.DataContext>
    <ContentControl  Content="{Binding Path=CurrentControl }"/>
</Window>

Imports System.ComponentModel

Public MustInherit Class ViewModelBase
    Implements INotifyPropertyChanged

#Region "INotifyPropertyChanged Members"
    Protected Sub RaisePropertyChanged(p As String)
        RaiseEvent INotifyPropertyChanged_PropertyChanged(Me, New PropertyChangedEventArgs(p))
    End Sub

    Private Event INotifyPropertyChanged_PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged
#End Region

End Class

using Microsoft.VisualBasic;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Data;
using System.Diagnostics;
using System.ComponentModel;

public abstract class ViewModelBase : INotifyPropertyChanged
{

	#region "INotifyPropertyChanged Members"
	protected void RaisePropertyChanged(string p)
	{
		if (INotifyPropertyChanged_PropertyChanged != null) {
			INotifyPropertyChanged_PropertyChanged(this, new PropertyChangedEventArgs(p));
		}
	}

	private event PropertyChangedEventHandler INotifyPropertyChanged.INotifyPropertyChanged_PropertyChanged;
	#endregion

}

Namespace MainViewModelNameSpace
    Public Class MainViewModel
        Inherits ViewModelBase

        Private _CurrentControl As UserControl
        Public Property CurrentControl() As UserControl
            Get
                Return _CurrentControl
            End Get
            Set(ByVal value As UserControl)
                _CurrentControl = value
            End Set
        End Property

        Sub New()
            _CurrentControl = New InputTabControl
        End Sub


    End Class
End Namespace

using Microsoft.VisualBasic;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Data;
using System.Diagnostics;
namespace MainViewModelNameSpace
{
	public class MainViewModel : ViewModelBase
	{

		private UserControl _CurrentControl;
		public UserControl CurrentControl {
			get { return _CurrentControl; }
			set { _CurrentControl = value; }
		}

		public MainViewModel()
		{
			_CurrentControl = new InputTabControl();
		}


	}
}

<Window x:Class="MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:new_termonal_06_12"
        xmlns:vm="clr-namespace:new_termonal_06_12.MainViewModelNameSpace"
        mc:Ignorable="d"
        Height="auto" Width="auto" WindowState="Maximized">
    <Window.DataContext >
        <vm:MainViewModel/>
    </Window.DataContext>
    <ContentControl  Content="{Binding Path=CurrentControl }"/>
</Window>

 Dim f1 As New frm
 With f1
.MdiParent = Me
.Show()
' все действия
end with 

<DataTemplate DataType="{x:Type viewModels:BooksViewModel}">
       <views:BooksView />
</DataTemplate>

<DataTemplate DataType="{x:Type viewModels30:BooksViewModel}">
       <views:BooksView30 />
</DataTemplate>