Using `MvxReference.Strong` in MvvmCross involves managing strong references to actions or methods in your view models. This is particularly relevant when subscribing to messages via the `IMvxMessenger` interface. Here are some best practices for using strong references effectively:
1. Manual Subscription Management**
When using strong references, it's crucial to manually manage subscriptions to prevent memory leaks. This means you must explicitly unsubscribe from messages when your view model is no longer needed or when the associated view is deactivated or destroyed.csharp
// Example of subscribing with a strong reference
var subscriptionToken = MvxMessenger.Subscribe(HandleMessage, MvxReference.Strong);
// Later, when the view model is no longer needed
MvxMessenger.Unsubscribe(subscriptionToken);
2. Implement Lifecycle Hooks**
MvvmCross views (like `MvxActivity` or `MvxViewController`) provide lifecycle hooks such as `ViewAppearing`, `ViewDisappearing`, `ViewCreated`, and `ViewDestroy`. Use these hooks to manage your subscriptions:- Subscribe in `ViewAppearing` or `ViewCreated`.
- Unsubscribe in `ViewDisappearing` or `ViewDestroy`.
3. Avoid Static References**
Ensure that your view models do not hold static references to any objects. Static references can prevent garbage collection and lead to memory leaks.4. Single Instance Logic**
If multiple instances of a view model can exist concurrently, implement logic to ensure only one instance subscribes to a particular message. You can use `MvxMessenger.RequestPurge` to remove old subscriptions.5. Monitor Subscriptions**
Use methods like `HasSubscriptionsFor` to check if there are existing subscriptions for a message type before creating new ones. This helps prevent duplicate subscriptions.6. Use Weak References When Possible**
While strong references provide reliability, consider using weak references (`MvxReference.Weak`) when possible to allow for automatic garbage collection of view models when they are no longer referenced by the view.7. Test Thoroughly**
Thoroughly test your application to ensure that view models are properly garbage collected and that subscriptions are correctly managed. Use tools like memory profilers to detect potential leaks.By following these practices, you can effectively manage strong references in MvvmCross and prevent common issues like memory leaks.
Citations:[1] https://www.mvvmcross.com/documentation/fundamentals/viewmodel-lifecycle
[2] https://www.codefactor.io/repository/github/mvvmcross/mvvmcross/source/develop/MvvmCross.Plugins/Messenger/IMvxMessenger.cs
[3] https://stackoverflow.com/questions/27008035/mvvmcross-memory-leak-because-of-not-disposed-viewmodels
[4] https://learn.microsoft.com/en-us/archive/msdn-magazine/2014/august/windows-phone-build-mvvm-apps-with-xamarin-and-mvvmcross
[5] https://stackoverflow.com/questions/21133533/best-way-to-send-an-async-message-to-the-parent-viewmodel-before-closing
[6] https://www.mvvmcross.com/mvvmcross-5-release/
[7] https://www.mvvmcross.com/documentation/plugins/messenger
[8] https://stackoverflow.com/questions/19757437/how-to-unit-test-mvvmcross-with-imvxmessenger/33912967
[9] https://stackoverflow.com/questions/54040726/mvvmcross-android-appears-to-be-keep-hold-of-viewmodels-and-never-disposing-w