Nullable Microsoft.Toolkit.Mvvm Ioc.Default.GetService vs. GalaSoft.MvvmLight SimpleIoc.Default.GetInstance

[myokeeh]

What's best practice for addressing Ioc.Default.GetService possibly returning null? Do I chase all references and do null checks? I'm fine with it if that's the case, but just wondering why it might return null compared to MVVM Light SimpleIoc.Default.GetInstance. Without looking at source code, I suppose it can also return null, but developed prior to the C# concept of nullable?

//Toolkit.Mvvm
public SettingsViewModel? SettingsViewModel => Ioc.Default.GetService<SettingsViewModel>();

//MvvmLight
public SettingsViewModel SettingsViewModel => SimpleIoc.Default.GetInstance<SettingsViewModel>();

Looked at latest guidance on migration docs: https://github.com/windows-toolkit/MVVM-Samples/blob/01465e5d114441e0f50279853361670a4767e80b/docs/mvvm/MigratingFromMvvmLight.md

cc: @Sergio0694, thoughts?

[myokeeh]

Or maybe I should just be using GetRequiredService?

[Sergio0694]

Hey @myokeeh, sorry for the delay, missed the notification! 😄

The GetService method returns null because that's the official contract from the IServiceProvider interface (see here). I would imagine that it's not that MvvmLight wasn't returning null as well, it's more likely that it was just missing the nullable annotation, so you didn't see the return type as nullable, as you suggested. If you want to ensure the requested type is present and throw otherwise, then yeah I'd recommend using GetRequiredService instead, I added that extension specifically for this scenario 👍

Hope this helps!