CODEWITHSUNDEEP
c#wpfmvvmmef
Fabrizio Stellato
Fabrizio Stellato

Reputation: 1901

MEF automaically resolve object

I need to use MEF and MVVM pattern for my WPF app.

Actually I have a ViewModel so definied:

[Export]
[PartCreationPolicy(CreationPolicy.NonShared)]
class MainVM 
{        
    IServiceA serviceA;        
    IServiceB serviceB;

    [ImportingConstructor]
    public MainVM(IServiceA serviceA, IServiceB serviceB)
    {
        this.serviceA = serviceA;
        this.serviceB = serviceB;

        System.Diagnostics.Debug.WriteLine(serviceA.Time);
    }
}

For the VM retrieving, I make use of a VMLocator, so made:

class ViewModelLocator
{
    static ViewModelLocator instance;

    public MainVM MainVM
    {
        get
        {
            MainVM output = MefBootstrap.Container.GetExportedValue<MainVM>();
            return output;
        }
    }

    protected ViewModelLocator()
    {

    }

    public static ViewModelLocator Instance
    {
        get
        {
            return instance ?? (instance = new ViewModelLocator());
        }
    }
}

called from XAML:

DataContext="{Binding Source={x:Static provider:ViewModelLocator.Instance}, Path=MainVM}"

This code actually works.

What I wonder if realizable is to automatically Import VM using only MEF ExportAttribute [Import] on the attribute declaration of VMLocator instead of using GetExportValue() method.

Is the any solution ?

Upvotes: 0

Views: 277

Answers (1)

Karolis Kajenas
Karolis Kajenas

Reputation: 1543

It does not work because you manually create ViewModelLocator. Since you create it manually IoC(MEF) does not have control over this instance creation and thus it will not [Import] dependency(MainVM) from container into your property.

So to address the question "Is there any solution?":

Here is an example of how to leverage MEF in MVVM context.

I strongly advice you go with PRISM. It already has it done for you. I'd rather not reinvent the wheel especially this one.

Upvotes: 1

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