XAML template binding in Windows 8 - data-binding

Question

I am walking through Windows Store Sample Application XAML Twitter Client 1, to get the same features in my own application. But i can't get binding work in 1 to 1 sample page.
This is my grid for displaying friends:
<GridView x:Name="FriendsGrid"
Grid.Row="2"
Grid.Column="1"
HorizontalAlignment="Left"
VerticalAlignment="Top"
Margin="10,10,0,0"
ItemsSource="{Binding Friends}"
ItemTemplate="{StaticResource FriendItemTemplate}"
Grid.ColumnSpan="2">
<GridView.DataContext>
<Model:FriendsViewModel/>
</GridView.DataContext>
Template for binding:
<Page.Resources>
<DataTemplate x:Key="FriendItemTemplate">
<Grid Height="200" Width="300">
<Grid.RowDefinitions>
<RowDefinition/>
<RowDefinition/>
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition/>
<ColumnDefinition/>
</Grid.ColumnDefinitions>
<Image HorizontalAlignment="Left"
Height="80" Width="130"
Margin="10,10,0,0"
VerticalAlignment="Top"
Source="{Binding RealPhoto}"
Stretch="UniformToFill"/>
<TextBlock Grid.Column="1"
HorizontalAlignment="Left"
Margin="10,10,0,0"
TextWrapping="Wrap"
VerticalAlignment="Top"
Height="80"
Width="130"
Text="{Binding FirstName}"/>
<TextBlock HorizontalAlignment="Left"
Margin="10,10,0,0"
Grid.Row="1"
TextWrapping="Wrap"
Text="{Binding LastName}"
VerticalAlignment="Top"
Width="280" Height="80"
Grid.ColumnSpan="2" />
</Grid>
</DataTemplate>
</Page.Resources>
In my code-behind file:
private FriendsViewModel _model;
public MyPage()
{
this.InitializeComponent();
_model = new FriendsViewModel();
FriendsGrid.DataContext = _model;
}
Than i populate model, in application i see exactly the same items count that i`ve added, but items are empty. Using debug i see, that model is not empty.
Also when i am hard-coding values in templates, they are visible.
Test project on GitHub

Answer 1

I forgot to add getters and setters to properties of my model. Initially i had this:
public double Uid;
Than i added {get; set;}
[DataContract]
public class Friend
{
[DataMember(Name = "uid")]
public double Uid { get; set; }
[DataMember(Name="first_name")]
public string FirstName { get; set; }
[DataMember(Name="last_name")]
public string LastName { get; set; }
[DataMember(Name="online")]
public bool Online { get; set; }
[DataMember(Name = "photo")]
public string Photo { get; set; }
public ImageSource RealPhoto { get; set; }
}

Answer 2

To see changes in your view model you need to implement INotifyPropertyChanged. Part of doing this is calling NotifyPropertyChanged on a property if its value changes.