wpf mvvm binding to sub viewmodel.property

I made an example as simple as possible.
I have a class ViewModelMain whose will implement several viewmodels.
I am trying to bind my slider value on a viewmodel in my ViewModelMain. Here my code:

MainWindow.xaml.cs
I set the datacontext here, don't know if it is realy a good idea.

public partial class MainWindow : Window { public MainWindow() { InitializeComponent(); VMMain vm = new VMMain(); this.DataContext = vm; } } 

MainWindow.xaml

<Window x:Class="WpfApplication1.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="MainWindow" Height="350" Width="525"> <Grid> <Slider Height="23" Name="page_slider" Width="100" Value="{Binding Path=p.NbrLine}" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Minimum="0" Maximum="10"/> <TextBox Text="{Binding Value, ElementName=page_slider, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" Height="28" HorizontalAlignment="Stretch" Name="Voiture1Label" VerticalAlignment="Stretch" Margin="0,110,0,172"></TextBox> </Grid></Window> 

ViewModelMain.cs ViewModelBase : the class which implement the INotifyPropertyChanged ModelPage : my model MyPage : my sub viewmode which is the viewmodel of ModelPage ViewModelMain : my final viewmodel which will implement more viewmodel

public class ViewModelBase : INotifyPropertyChanged { public event PropertyChangedEventHandler PropertyChanged; protected virtual void OnPropertyChanged(string propName) { if (PropertyChanged != null) { PropertyChanged(this, new PropertyChangedEventArgs(propName)); } } } public class ModelPage { public int NbrLine { get; set; } public int NbrCapsLock { get; set; } } public class MyPage : ViewModelBase { private ModelPage _model; public MyPage(ModelPage m) { _model = m; } public int NbrLine { get { return (_model.NbrLine); } set { if (_model.NbrLine == value) return; _model.NbrLine = value; OnPropertyChanged("NbrLine"); } } public int NbrCapsLock { get { return (_model.NbrCapsLock); } set { if (_model.NbrCapsLock == value) return; _model.NbrCapsLock = value; OnPropertyChanged("NbrCapsLock"); } } } public class ViewModelMain { public MyPage p; public ViewModelMain() { p = new MyPage(new ModelPage(){NbrLine = 5, NbrCapsLock = 1}); } } 

when i launch it, my slider is still on 0 doesn't understand why it is not on 5.