Can you provide an example of using ReloadFromBundle in MvvmCross

Overview of ReloadFromBundle in MvvmCross

In MvvmCross, `ReloadFromBundle` is a method used to restore the state of a ViewModel when an application is reactivated after being tombstoned. Tombstoning occurs when an application is suspended and its memory is reclaimed by the operating system, often due to low memory conditions. This method is crucial for maintaining the application's state across such interruptions.

How ReloadFromBundle Works

1. Saving State: Before an application is tombstoned, MvvmCross calls `SaveStateToBundle` on the ViewModel. This method allows you to save any necessary data into an `IMvxBundle`, which is then stored by MvvmCross.

2. Restoring State: When the application is reactivated, MvvmCross calls `ReloadFromBundle` on the ViewModel. This method receives the saved `IMvxBundle` as a parameter, allowing you to restore the previously saved data.

Example Implementation

Here's an example of how you might implement `SaveStateToBundle` and `ReloadFromBundle` in a ViewModel:

csharp
public class MyViewModel : MvxViewModel
{
    private readonly IMvxJsonSerializer _jsonSerializer;
    private MyParameterModel _initialParameter;

    public MyViewModel(IMvxJsonSerializer jsonSerializer)
    {
        _jsonSerializer = jsonSerializer;
    }

    protected override void SaveStateToBundle(IMvxBundle bundle)
    {
        base.SaveStateToBundle(bundle);
        bundle.Data["MyParameter"] = _jsonSerializer.Serialize(_initialParameter);
    }

    protected override void ReloadFromBundle(IMvxBundle state)
    {
        base.ReloadFromBundle(state);
        var serializedParameter = state.Data["MyParameter"];
        _initialParameter = _jsonSerializer.Deserialize(serializedParameter);
    }

    public override void Prepare(MyParameterModel parameter)
    {
        _initialParameter = parameter;
    }

    public override async Task Initialize()
    {
        await base.Initialize();
        // Use _initialParameter here
    }
}

Lifecycle of a ViewModel

The lifecycle of a ViewModel in MvvmCross includes several key methods:

- Construction: The ViewModel is created using dependency injection.
- Init: Initializes the ViewModel with navigation parameters.
- ReloadFromBundle: Restores state after tombstoning.
- Start: Called when initialization and rehydration are complete.
- Initialize: Initializes the ViewModel's data and tasks.

Challenges with ReloadFromBundle

Some developers have reported issues with `ReloadFromBundle` not being called, particularly in Xamarin.Forms applications. This might be due to the way tombstoning is handled in different platforms or versions of MvvmCross. For instance, in Xamarin.Forms, you might need to manually trigger these methods by hooking into page lifecycle events[4].

Testing Tombstoning

To test tombstoning and ensure `ReloadFromBundle` is called, you can use the Android developer option "Don't keep activities" or simulate it using `adb shell am kill `. However, this will disconnect you from the debugger, so logging is recommended for debugging purposes[4].