How does MvxReference.Strong affect the lifecycle of ViewModels

Strong References and ViewModel Lifecycle

In MVVM and MvvmCross, ViewModels are designed to manage data and business logic independently of the UI. A strong reference in this context typically refers to how a ViewModel holds onto its dependencies or data. Here's how strong references can impact the lifecycle of ViewModels:

1. Dependency Injection: MvvmCross uses Dependency Injection (DI) to provide dependencies to ViewModels. When a ViewModel holds strong references to its dependencies, it ensures that these dependencies remain available throughout the ViewModel's lifecycle. This is crucial for maintaining the state and functionality of the ViewModel[4].

2. Lifecycle Management: In MvvmCross, the lifecycle of a ViewModel is managed by the framework itself. The ViewModel's lifecycle includes methods like `Init`, `ReloadState`, `Start`, and others that help manage its state across different scenarios, such as tombstoning (when the app is suspended and resumed)[2][4]. Strong references can ensure that necessary data is retained during these lifecycle events.

3. Tombstoning and State Restoration: When an app undergoes tombstoning, MvvmCross provides mechanisms like `ReloadFromBundle` to restore the ViewModel's state. Strong references can be beneficial here by ensuring that critical data is preserved and restored correctly[4].

4. Memory Management: While strong references are useful for maintaining state, they can also lead to memory leaks if not managed properly. It's essential to ensure that strong references are released when appropriate to avoid retaining unnecessary objects in memory.

Impact on MvvmCross ViewModels

In MvvmCross, ViewModels are instantiated using the IoC container, which manages dependencies. Strong references within a ViewModel are typically used to hold onto these dependencies. This ensures that the ViewModel can operate effectively throughout its lifecycle, which is tied to the lifecycle of the associated view or navigation context.

However, it's crucial to avoid strong references to views or activities directly, as this can lead to memory leaks and violate the MVVM principle of separating the UI from the business logic. Instead, MvvmCross encourages using lifecycle-aware methods and data binding to manage interactions between the ViewModel and the view.

In summary, while `MvxReference.Strong` is not explicitly discussed, strong references in MvvmCross ViewModels are essential for maintaining dependencies and state across the ViewModel's lifecycle. However, they must be managed carefully to prevent memory issues.