interface IResourceProvider
{
    IEnumerable<Resource> GetResources();
}

class WindowsResourceProvider : IResourceProvider
{
    public IEnumerable<Resource> GetResources()
    {
        return NativeMethods.GetResources();            
    }    
}

class AndroidResourceProvider : IResourceProvider
{
    public IEnumerable<Resource> GetResources()
    {
        return FactoryProviderFactory.getInstance().getFactory().getProvider().execute(new GetResourcesCommandImpl());
    }    
}

class IOSResourceProvider : IResourceProvider
{
    public IEnumerable<Resource> GetResources()
    {
        return NSResourceManager.getResourcesWithKeyAndValueByLoadingResourceFromXibFileAndReturningErrorOnFailure();
    }    
}

interface IAsyncResourceProvider : IResourceProvider
{
    async IEnumerable<Resource> GetResourcesAsync();    
}

class WindowsResourceProvider : IAsyncResourceProvider
{
    public IEnumerable<Resource> GetResources()
    {
        return NativeMethods.GetResources();            
    }

    public async IEnumerable<Resource> GetResourcesAsync()
    {
        return NativeMethods.GetResourcesAsync();            
    }
}

var resourceProvider = ServiceLocator.Resolve<IResourceProvider>();
var resources = resourceProvider is IAsyncResourceProvider ?
    await ((IAsyncResourceProvider)resourceProvider).GetResourcesAsync() :
    resourceProvider.GetResources();