Can you provide an example of how to use SaveStateToBundle in MvvmCross

Using `SaveStateToBundle` in MvvmCross

In MvvmCross, the `SaveStateToBundle` method is crucial for saving the state of your ViewModel when the application is being tombstoned or goes into the background. This ensures that when the app resumes, you can restore the state using the `ReloadFromBundle` method. Here's a detailed example of how to use `SaveStateToBundle`:

Overview of the Process

1. Saving State: When your app is about to be tombstoned or goes into the background, MvvmCross calls the `SaveStateToBundle` method on your ViewModel. This method allows you to save any necessary data to an `IMvxBundle`.

2. Restoring State: When your app resumes, MvvmCross calls the `ReloadFromBundle` method, passing the saved `IMvxBundle`. You can then retrieve the saved data and restore your ViewModel's state.

Example Implementation

Let's consider a simple ViewModel that needs to save a parameter:

csharp
using MvvmCross.ViewModels;
using MvvmCross.Plugin.Json;

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

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

    // Method to save the state
    protected override void SaveStateToBundle(IMvxBundle bundle)
    {
        base.SaveStateToBundle(bundle);
        bundle.Data["MyParameter"] = _jsonSerializer.Serialize(_initialParameter);
    }

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

    // Prepare method to initialize the parameter
    public override void Prepare(MyParameterModel parameter)
    {
        _initialParameter = parameter;
    }

    // Initialize method for any async initialization
    public override async Task Initialize()
    {
        await base.Initialize();
        // Use _initialParameter here if needed
    }
}

public class MyParameterModel
{
    public string SomeProperty { get; set; }
}

Explanation

- Saving State: In the `SaveStateToBundle` method, you serialize your data (in this case, `_initialParameter`) using the `IMvxJsonSerializer` and store it in the `IMvxBundle`. This ensures that when the app is restored, you can retrieve this data.

- Restoring State: In the `ReloadFromBundle` method, you deserialize the data from the `IMvxBundle` back into your `_initialParameter`. This restores your ViewModel's state.

- Preparing the ViewModel: The `Prepare` method is used to initialize your ViewModel with parameters. When the app resumes, only the parameterless `Prepare` method is called, so it's your responsibility to save and restore any parameters using `SaveStateToBundle` and `ReloadFromBundle`.

This approach allows you to maintain your ViewModel's state across app lifecycle events, ensuring a seamless user experience.