How to reset all instances in IOC Container

Question

I have made an C# WPF Application using the MVVM Light framework. My Application uses the ViewModelLocator class to locate the viewmodels during runtime. The ViewModelLocator makes usage of the SimpleIoc class which also comes with the MVVM Light framework.

Here is my scenario: The user logs in an can use my application. On logout, i want to dispose/reset/recreate all viewmodel instances to provide a clean environment to the next user.

I tried to implement the Cleanup() method in the ViewModelLocator class but it is not working. Not working means that the (second) user sees the data from the user who was logged in before.

first try:

public static void Cleanup()
{
   SimpleIoc.Default.Reset();
}

second try:

public static void Cleanup()
{
   SimpleIoc.Default.Unregister<LoginViewModel>();
   SimpleIoc.Default.Unregister<TaskViewModel>();

   SimpleIoc.Default.Register<LoginViewModel>();
   SimpleIoc.Default.Register<TaskViewModel>();
}

third try (not what i want but it is a workaround):

public static void Cleanup()
{
   // I implemented the ICleanup interface in my viewmodels
   // The cleanup method clears all my variables eg: myCollection.clear();
   SimpleIoc.Default.GetInstance<LoginViewModel>().Cleanup();
   SimpleIoc.Default.GetInstance<TaskViewModel>().Cleanup();
}

How do i reset all instances in my ViewModelLocator class? I'm willing to use a more advanced Ioc Container if necessary.

What's wrong with the third approach? Can the objects not be reused? — Dustin Kingen
I have some logic in my constructors which prepare some things for the current user. This won't work any longer. I also have to write a lot of code which needs to be maintained (cleanup method for every viewmodel). The approach to throw away the old instances seems far more straightforward to me. — Joel
According to the MVVM Light maintainer this is the recommended approach. SimpleIoc - can it provide new instance each time required?. If that doesn't fit your architecture then it might be better to switch to another IOC. — Dustin Kingen
I've used Simple Injector and AutoFac. IOCs aren't hard to write and there's a pretty good comparison at IOC Battle. — Dustin Kingen

Viv Viv · Accepted Answer · 2013-06-11T12:28:30

With SimpleIoC

I'd add a public static property with a private string backend for a unique Key

something like

private static string _currentKey = System.Guid.NewGuid().ToString();
public static string CurrentKey {
  get {
    return _currentKey;
  }
  private set {
    _currentKey = value;
  }
}

and have the cleanup method to unregister VM's with current key and finally reset the current key(invoke on each app reset stage):

public static void Cleanup() {
  SimpleIoc.Default.Unregister<LoginViewModel>(CurrentKey);
  ...
  CurrentKey = System.Guid.NewGuid().ToString();
}

and when calling GetInstance(...) just pass in the static CurrentKey.

SimpleIoc.Default.GetInstance<LoginViewModel>(ViewModelLocator.CurrentKey);

How to reset all instances in IOC Container

1 Answers