Binding object xaml to property in viewmodel

  <StackPanel Grid.Column="1" Grid.Row="1"
      HorizontalAlignment="Center" Margin="40,30" Width="220"
      DataContext="{Binding  TempPersona,Mode=TwoWay,
                   UpdateSourceTrigger=PropertyChanged}">
        <TextBox x:Name="txtNombre" Width="160" Margin="0,6,0,18"
           Text="{ Binding Path=Nombre,
                Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}">
        </TextBox>
        <TextBox x:Name="txtApellidos" Width="160" Margin="0,0,0,18"
            Text="{ Binding Path=Apellidos, Mode=TwoWay,
               UpdateSourceTrigger=PropertyChanged}"></TextBox>
        <TextBox x:Name="txtDireccion" Width="160" Margin="0,0,0,18"
            Text="{ Binding Path=Direccion, Mode=TwoWay,
              UpdateSourceTrigger=PropertyChanged}">
        </TextBox>
        <TextBox x:Name="txtContacto" Width="160" Margin="0,0,0,18"
             Text="{ Binding Path=Contacto,
              Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}">
        </TextBox>
    </StackPanel>
<StackPanel Orientation ="Horizontal"
          Grid.ColumnSpan="2" Grid.Row="2"
          HorizontalAlignment="Center" Margin="70,0" Width="280">
   <Button Content="Añadir" Height="30" Width="120"  Margin="20,0,0,10"
      CommandParameter ="{Binding}"
      Command="{Binding RelativeSource={RelativeSource
                               AncestorType={x:Type Window}},
          Path=DataContext.AnadirAVM}">
       </Button>
</StackPanel>

private Persona _tempPersona;
        public Persona TempPersona
        {
            get { return _tempPersona; }
            set
            {
                if (_tempPersona != value) //Here value is null
                {
                    _tempPersona = value;
                    OnPropertyChanged("TempPersona");
                }
             }
        }

  private ICommand _anadirAVM;
  public ICommand AnadirAVM
{
get { return _anadirAVM ??
         (_anadirAVM = new RelayCommand((parameter)
                =>  AnadirAVMAction(parameter))); }
    }

private void AnadirAVMAction(object parameter)
{
        TempPersona = parameter as Persona;
        targetAVM.Crear(TempPersona);
    MessageBox.Show("Register Added");
}