Raise usercontrol commands from a parent window using mvvm pattern - wpf

Question

My WCF application supports downloading books from a remote service. The user sends a request to the service to download a book, the service gets the request and downloads the book. in response, it sends the download progress for the requested book.
Each element in the BookContainer is a userControl of Book.xaml and its logic represented by bookviewmodel.cs class.
When the user clicks on each book element in the BookContainer.xaml window, the click command inside the bookviewmodel is raised as expected.
I need the help to implement "DownlaodAllCommand" inside containerviewmodel to raise each DownloadCommand of each book.
How should it be implemented using the mvvm pattern.
BookContainer view :
https://onedrive.live.com/redir?resid=3A8F69A0FB413FA4!124&authkey=!ANdfYAk6f0Vf-8s&v=3&ithint=photo%2cpng
code behind:
BookContainer.xaml:
<Window x:Name="BookContainer"
DataContext="{Binding Source={StaticResource Locator}, Path=ContainerViewModel}">
<DockPanel>
<ItemsControl DockPanel.Dock="Top" ItemsSource="{Binding Books}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<StackPanel Orientation="Vertical" />
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl.ItemTemplate>
<DataTemplate >
<Controls:BookControl />
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
<Button DockPanel.Dock="Bottom" Command="{Binding DownloadAllCommand}" Content="Download All" > </Button>
</DockPanel>
</Window>
ContainerViewModel
public class ContainerViewModel : ViewModelBase
{
private ObservableCollection<BookViewModel> books;
public ObservableCollection<BookViewModel> Books
{
get
{
if (books == null)
{
// Not yet created.
// Create it.
books = new ObservableCollection<BookViewModel>();
}
return books;
}
}
private ActionCommand _DownloadAllCommand;
public ICommand DownloadAllCommand
{
get
{
if (_DownloadAllCommand == null)
{
_DownloadAllCommand = new ActionCommand(OnDownloadAllCommand, CanDownloadAllCommand);
}
return _DownloadAllCommand;
}
}
private void OnDownloadAllCommand()
{
// help !
}
private bool CanDownloadAllCommand()
{
return true;
}
}
Book.xaml
<UserControl
<Label Grid.Row="0">Title</Label>
<Label Grid.Row="1">Author</Label>
<Label Grid.Row="2">Description</Label>
<TextBlock Grid.Row="0" Grid.Column="1" Text="{Binding Title}"/>
<TextBlock Grid.Row="1" Grid.Column="1" Text="{Binding Author}"/>
<TextBlock Grid.Row="2" Grid.Column="1" Text="{Binding Description}"/>
<Button Grid.Column="2" Grid.RowSpan="3" Command="{Binding DownloadCommand}" Content="Download" />
<Ellipse Grid.Column="3"
Height="20" Width="20"
Stroke="Black"
StrokeThickness="0.5"
HorizontalAlignment="Center"
Grid.Row="1"
/>
<Controls:PieSlice Grid.Column="3" Grid.Row="1" Stroke="Black" Fill="Black"
Height="20" Width="20"
StartAngle="0" EndAngle="{Binding Percent}"
HorizontalAlignment="Center" />
</UserControl>
BookViewModel
public class BookViewModel : ViewModelBase
{
public delegate void DownloadRequest(string name);
public event DownloadRequest OnDownalodRequest;
public BookViewModel(BookModel model)
{
this.Book = model;
}
private ActionCommand _DownloadCommand;
public ICommand DownloadCommand
{
get
{
if (_DownloadCommand == null)
{
_DownloadCommand = new ActionCommand(OnDownloadCommand, CanDownloadCommand);
}
return _DownloadCommand;
}
}
protected virtual void OnDownloadCommand()
{
if (OnDownalodRequest != null)
{
OnDownalodRequest.Invoke(this.Author);
}
}
}
BookModel
public class BookModel
{
public string Title { get; set; }
public string Author { get; set; }
public string Description { get; set; }
public Status Status { get; set; }
}

Answer 1

Insid the ContainerViewModel, method OnSaveAllCommand():
Books.ToList().Foreach(book =>
{
if(book.SaveCommand.CanExecute() == false) return;
book.SaveCommand.Execute()
}
);
but take in account that this is a bad practice to use a viewmodel from another viewmodel, try to perform viewmodels communnication on a model level.