General Actions:
Last modified on August 15, 2012 17:20
Cocktail integrates MEF with Caliburn Micro. This allows for wiring the ViewModels and its dependencies through dependency-injection for loose-coupling of all the parts that make up the application, ease of extending an application, and ease of maintenance.
At this point we assume that you are somewhat familiar with MVVM and Caliburn Micro. For more information on Caliburn Micro, please visit the Caliburn Micro Documentation.
Basic ViewModel
Caliburn Micro offers a number of base classes to build ViewModels with certain attributes and behavior. In it’s most basic form, though, a ViewModel is simply a POCO.
| C# | using System.ComponentModel.Composition; using Caliburn.Micro; [Export] public class BasicViewModel : Screen { // Add Data Properties and Actions } |
In the above example we are using the Caliburn Micro Screen class as the base. The only other thing required is the [Export] attribute that is used to make the ViewModel available to MEF, and allow MEF to create instances as required by the application and inject the necessary dependencies into it. The above example doesn’t have any dependencies.
ViewModel with Dependencies
The most common dependency of a ViewModel is the UnitOfWork. We use it to retrieve and save data and perform business logic on the data. Just like the ViewModels, the UnitOfWork is exported through MEF. Most often though, the UnitOfWork is exported not by the concrete type, but by an interface, so that it can be substituted for unit testing for example.
| C# | using System.ComponentModel.Composition; using Caliburn.Micro; [Export] public class BasicViewModel : Screen { private readonly IUnitOfWork<Customer> _uow; [ImportingConstructor] public BasicViewModel(IUnitOfWork<Customer> uow) { _uow = uow; } // Add Data Properties and Actions } |
ViewModel Composition
More complex ViewModels are often composed together of multiple smaller ViewModels. This can be achieved through the same dependency injection mechanisms. Communication between the composed ViewModels is often done through messaging with the help of an event aggregator. Caliburn Micro offers such an event aggregator and Cocktail makes it available through MEF.
| C# | using System.ComponentModel.Composition; using Caliburn.Micro; using Cocktail; public class DoSomethingMessage { } [Export] public class MenuViewModel : Screen { public void MenuItemClicked() { EventFns.Publish(new DoSomethingMessage()); } } [Export] public class WorkspaceViewModel : Screen, IHandle<DoSomethingMessage> { public WorkspaceViewModel() { EventFns.Subscribe(this); } public void Handle(DoSomethingMessage message) { // Do something } }// [Export] public class Shell : Screen { [ImportingConstructor] public Shell(MenuViewModel menuViewModel, WorkspaceViewModel workspaceViewModel) { MenuViewModel = menuViewModel; WorkspaceViewModel = workspaceViewModel; } public IScreen MenuViewModel { get; private set; } public IScreen WorkspaceViewModel { get; private set; } // Add Data Properties and Actions } |