How to navigate through windows with MVVM Light for WPF?
I usually use a ContentControl
to display dynamic content. It's Content
property is usually bound to a CurrentViewModel
property in the parent ViewModel
, and DataTemplates
are used to tell WPF how to draw the child ViewModels
.
To change views, simply change the CurrentViewModel
property in the parent ViewModel
You can find an example at this article of mine
Eventually I did it this way.
Following the idea of o_q, I created NavigationWindow as MainWindow and changed all the the views to page.
Then, I created an inteface and a class which using Navigation:
public interface INavigationService
{
event NavigatingCancelEventHandler Navigating;
void NavigateTo(Uri pageUri);
void GoBack();
}
public class NavigationService : INavigationService
{
private NavigationWindow _mainFrame;
#region Implementation of INavigationService
public event NavigatingCancelEventHandler Navigating;
public void NavigateTo(Uri pageUri)
{
if (EnsureMainFrame())
{
_mainFrame.Navigate(pageUri);
}
}
public void GoBack()
{
if (EnsureMainFrame()
&& _mainFrame.CanGoBack)
{
_mainFrame.GoBack();
}
}
#endregion
private bool EnsureMainFrame()
{
if (_mainFrame != null)
{
return true;
}
_mainFrame = System.Windows.Application.Current.MainWindow as NavigationWindow;
if (_mainFrame != null)
{
// Could be null if the app runs inside a design tool
_mainFrame.Navigating += (s, e) =>
{
if (Navigating != null)
{
Navigating(s, e);
}
};
return true;
}
return false;
}
}
Then, in viewModelLocator I created all the const string nedded to store the paths to my views:
public class ViewModelLocator
{
#region Views Paths
public const string FrontendViewPath = "../Views/FrontendView.xaml";
public const string BackendViewPath = "../Views/BackendView.xaml";
public const string StartUpViewPath = "../Views/StartUpView.xaml";
public const string LoginViewPath = "../Views/LoginView.xaml";
public const string OutOfOrderViewPath = "../Views/OutOfOrderView.xaml";
public const string OperativeViewPath = "../Views/SubViews/OperativeView.xaml";
public const string ConfigurationViewPath = "../Views/SubViews/ConfigurationView.xaml";
#endregion
}
In App.cs, in the Application_Startup event handler, with the help of Unity IoC I registered a singleton of NavigationService:
public partial class App : System.Windows.Application
{
private static IUnityContainer _ambientContainer;
public static IServiceLocator AmbientLocator { get; private set; }
...
private void Application_Startup(object sender, System.Windows.StartupEventArgs e)
{
_ambientContainer =
new UnityContainer();
_ambientContainer.RegisterType<INavigationService, NavigationService>(new ContainerControlledLifetimeManager());
AmbientLocator = new UnityServiceLocator(_ambientContainer);
ServiceLocator.SetLocatorProvider(() => AmbientLocator);
Now, in my ViewModelLocator, I can register a "Galasoft" message to catch all the events and navigate to a page; in the constructor I have:
public ViewModelLocator()
{
CreateMain();
CreateFrontend();
CreateBackend();
CreateStartUp();
CreateOperative();
CreateLogin();
CreateConfiguration();
CreateOutOfOrder();
// Set Startup Page...
ServiceLocator.Current.GetInstance<INavigationService>().NavigateTo(new Uri(StartUpViewPath, UriKind.Relative));
Messenger.Default.Register<MoveToViewMessage>(this, message =>
{
switch (message.StateInfo.StateType)
{
case StateType.StartUpState:
ServiceLocator.Current.GetInstance<INavigationService>().NavigateTo(new Uri(StartUpViewPath,UriKind.Relative));
break;
case StateType.LoginState:
ServiceLocator.Current.GetInstance<INavigationService>().NavigateTo(new Uri(LoginViewPath, UriKind.Relative));
break;
case StateType.OperativeState:
ServiceLocator.Current.GetInstance<INavigationService>().NavigateTo(new Uri(OperativeViewPath, UriKind.Relative));
break;
case StateType.ConfigurationState:
ServiceLocator.Current.GetInstance<INavigationService>().NavigateTo(new Uri(ConfigurationViewPath, UriKind.Relative));
break;
case StateType.ClosedState:
case StateType.OutOfOrderState:
ServiceLocator.Current.GetInstance<INavigationService>().NavigateTo(new Uri(OutOfOrderViewPath, UriKind.Relative));
break;
default:
ServiceLocator.Current.GetInstance<INavigationService>().NavigateTo(new Uri(StartUpViewPath, UriKind.Relative));
break;
}
});
}
In this way I keep all the viewModels "ignorant"... they don't know anything about navigation, plus I don't have code behind.
If I need to navigate by using a button from a view I can resolve NavigationService from the connected viewModel and navigate to the Page I need.
And, most important thing, it works!