Tuesday, May 15, 2012

Getting Started with Cocoon Navigation – The Cocoon Bootstrapper

In my last post I introduced the navigation framework that is included as part of the freely available Cocoon framework (open source on CodePlex). This framework is designed to make page based Metro-style applications easy to construct in managed languages on Windows 8.

I previously discussed how easy it was to implement the Model-View-ViewModel (MVVM) pattern with Cocoon by simply annotating your view and view models with the ‘PageExport’ and ‘ViewModel’ export attributes respectively. Any view model can then navigate to another page by calling the INavigationManager.NavigateTo(…) method.

Since the Cocoon navigation framework is built on top of the Managed Extensibility Framework (MEF), the application is composed with the required dependencies as the user navigates through the application. MEF is a composition framework that is built into the .Net framework, that enables the construction of loosely-coupled, easily maintainable and testable applications to be composed automatically at run time. An introductory guide for those who are not familiar with MEF is available here.

What I have not covered previously however was how to navigate to the application’s first page when it is launched,

Launching Navigation Using The Cocoon Bootstrapper

To simplify the initialization of Cocoon based applications the framework includes the ‘CocoonBootstrapper’ class that can be used at startup. This manages the configuration of MEF for the most common scenarios, initialization of services and activation of the application.

To use the Cocoon bootstrapper you must first create an application specific class derived from the abstract ‘CocoonBootstrapper’ as shown below. For basic applications this class can be left empty, although the base implementation provides a number of extensibility points to enable more advanced features.

public class AppBootstrapper : CocoonBootstrapper
{
}


The next stage is to edit your application’s ‘App.xaml.cs’ file. Much of the code included with the Visual Studio templates can be removed (since this is handled by Cocoon) and the newly created bootstrapper is initialized as part of the constructor.


sealed partial class App : Application
{
    public App()
    {
        this.InitializeComponent();
 
        // Create and initialize the application bootstrapper
 
        AppBootstrapper bootstrapper = new AppBootstrapper();
        bootstrapper.Initialize();
    }
}


Defining the Application Home Page

The final step is to define the view and (optionally) the view model that is to be shown when your application is launched. Whilst the home page name can be modified the default value defined by the ‘SpecialPageNames.HomePage’ constant is generally all that is required.

Therefore the home page view is annotated as,

[PageExport(SpecialPageNames.HomePage)]
public sealed partial class HomePage : LayoutAwarePage
{
    public HomePage()
    {
        this.InitializeComponent();
    }
}

and the view model annotated as,

[ViewModelExport(SpecialPageNames.HomePage)]
public class HomeViewModel
{
    ...
}


The Cocoon navigation framework will then automatically locate, create and wire-up the home page on application launch.

Summary

Over the last two posts I have shown how easy the Cocoon navigation framework makes launching and navigating around Metro-style Windows 8 applications using the MVVM pattern. In the upcoming posts I will discuss some of the more advanced features you get when adopting Cocoon for navigation.

As usual the code is freely available for download from the Cocoon CodePlex site (to get the latest version go to the “Source Code” tab, select the first change set and use the “Download” link).
Post a Comment