Persist the View and ViewModel

[pellea]

Hello,

Is it possible to persist the View and ViewModel using a DI container ? I don't want my views to be created each time because of the "heavy load" of the data.

Regards, Adrien.

[saguiitay]

I would also love to see some way of persisting the ViewModel (perhaps some form of caching service?)

[pellea]

Usually I use Prism with Unity container to achieve that.

[qmatteoq]

Template10 doesn't come with its own DI implementation, but you can absolutely use it with any other DI container, like Unity or SimpleIoC

[pellea]

I found 2 possible ways to do it but ... The Resolve() method is never used. The other method ResolveForPage() is called when the DataContext is null. How do I get the ViewModel in the view in that case? Is it possible to have constructor injection ?

[JerryNixon]

We can easily handle the view model but not the view. Not until we add Navigate To Instance too the Navigation Service. We NEED an injection sample.

[JerryNixon]

Resolve for page will automatically inject the returned result into any pages data connect. But it is only an alternative to a view model locator which can easily implement injection. It's a one or the other approach, to be honest. Many developers prefer the locator approach. I could go either way.

[JerryNixon]

Persist an entire view model? Hmm. Maybe we need a serializer util to help with that. Not a common approach I will warm you though.

[jhalbrecht]

First thing I do with a new project is add MvvmLight libs only via nuget. There is an MvvmLight Sample in the Template10 repository. I use MvvmLight for not only my view models but inject my services, repositories etc....

in .xaml code behind I can get a single instance I sometimes use with x:Bind;

public MainPageViewModel ViewModel => SimpleIoc.Default.GetInstance<MainPageViewModel>();

Be sure in ViewModelBase.cs

// public abstract class ViewModelBase : Template10.Mvvm.ViewModelBase
// change to:
    public abstract class ViewModelBase :
    GalaSoft.MvvmLight.ViewModelBase, Template10.Services.NavigationService.INavigable
[...]

I use the MvvmLight ViewModelLocator.cs

   public class ViewModelLocator
    {
        static ViewModelLocator()
        {
            ServiceLocator.SetLocatorProvider(() => SimpleIoc.Default);
            SimpleIoc.Default.Register<IMyDataService, MyDataService>();
            SimpleIoc.Default.Register<MainPageViewModel>();
        }
        public MainPageViewModel Main => ServiceLocator.Current.GetInstance<MainPageViewModel>();

wiring it up in

App.xaml

 <viewModels:ViewModelLocator x:Key="Locator"
                                         d:IsDataSource="True" />

MainPage.xaml

<Page
[...]
    DataContext="{Binding Main, Source={StaticResource Locator}}"
>

In MainPageViewModel.cs

private readonly IMyDataService _myDataService;

 public MainPageViewModel(IMyDataService myDataService)
        {
            _myDataService = myDataService;
        }

[pellea]

"Persist" was not the better word to explain what I tried to do. Usually I have all my ViewModel in the container. Everything is resolve using constructor injection. I use this "way" because I don't want to reload every time the ViewModel between each navigation of pages (and ultimatly I shared ViewModels between pages. I know some people don't like that). If I need to "persist" the ViewModel, I add them to the container with the ContainerControlledLifetimeManager (with Unity).

How do I do constructor injection (in the view) ? This is not possible in this library ...