MEF进出口无效

Question

I am trying to do a WPF application without using prism.When I tried to get my viewmodel in the view through mef by impoting constructor it not working.Also I have a property injection in my code that is also giving a null reference. Is this because of not overriding composite container, if so how/where to give a composite container in an application without prism. My code is like this In xaml file design instance is set to viewmodel and cs file is like

MainWindow.xaml.cs

public MainWindow()
    {
        InitializeComponent();            
    }

    [ImportingConstructor]
    public MainWindow(MainWindowViewModel viewModel) :this()
    {
        this.DataContext = viewModel;
        this.ViewModel = viewModel;
    }
    public MainWindowViewModel ViewModel { get; set; }

[Export] 
public class MainWindowViewModel 
{    
}

the breakpoint at the constructor of MainWindow.xaml.cs is not hitting at all.Inside viewmodel the property injection is also not hitting. How can I resolve this problem?

Answer 1

Here's an example using PRISM 5 but it'll work the same way in PRISM 6.2.0.

You'll need to remove the startup uri from app.xaml. Then make sure you have the PRISM.MEF NuGet package installed. Write a bootstrapper like the one below. (Note that the bootstrapper base class has a range of methods to override with a proper place for all this setup. I have stuck it all in one method for simplicity.)

public class MyBootstrapper : MefBootstrapper
{
    protected override DependencyObject CreateShell()
    {            
        var catalog = new AggregateCatalog();
        catalog.Catalogs.Add(new AssemblyCatalog(typeof(MyBootstrapper).Assembly));
        var container = new CompositionContainer(catalog);
        var shell = container.GetExport<MainWindow>().Value;
        shell.Show();
        return shell;
    }
}

Add an Export attribute to your MainWindow. That will be needed for this line in the bootstrapper:

var shell = container.GetExport<MainWindow>().Value;

[Export]
public partial class MainWindow : Window{}

Now all that is left is to run the bootstrapper:

public partial class App : Application
{
    protected override void OnStartup(StartupEventArgs e)
    {
        var bootstrapper = new MyBootstrapper();
        bootstrapper.Run();
    }
}

Update

You can get a pretty good handle on MEF by doing the example described here:

https://msdn.microsoft.com/en-us/library/dd460648(v=vs.110).aspx

Update

Here's a cleaner way of implementing the bootstrapper.

    public class MyBootstrapper : MefBootstrapper
    {
        protected override AggregateCatalog CreateAggregateCatalog()
        {
            return new AggregateCatalog();
        }

        protected override void ConfigureAggregateCatalog()
        {
            AggregateCatalog.Catalogs.Add(new AssemblyCatalog(typeof(MyBootstrapper).Assembly));
        }      

        protected override CompositionContainer CreateContainer()
        {
            return new CompositionContainer(AggregateCatalog);
        }

        protected override void ConfigureContainer()
        {
            base.ConfigureContainer();
        }

        protected override DependencyObject CreateShell()
        {
            var shell = Container.GetExport<MainWindow>().Value;
            shell.Show();
            return shell;
        } 
    }