How does JSON serialization work with SaveStateToBundle in MvvmCross

Overview of Tombstoning and State Saving

Tombstoning is a process where an application's state is saved when it is suspended or terminated due to low memory conditions, especially on platforms like Android. MvvmCross provides methods to handle this situation by saving and restoring the ViewModel's state using `SaveStateToBundle` and `ReloadFromBundle`.

Using JSON Serialization

When you need to save complex data structures, such as objects, JSON serialization is highly recommended. MvvmCross provides an `IMvxJsonSerializer` interface that can be used to serialize and deserialize objects to and from JSON strings.

Steps to Use JSON Serialization with SaveStateToBundle

1. Inject IMvxJsonSerializer: In your ViewModel, inject an instance of `IMvxJsonSerializer`. This is typically done through the constructor.

2. Override SaveStateToBundle: In your ViewModel, override the `SaveStateToBundle` method. This method is called when the application needs to save its state.

3. Serialize Data: Use the `IMvxJsonSerializer` to serialize any data you want to save into a JSON string. This could be a custom object or any other serializable data.

4. Store Serialized Data: Store the serialized JSON string in the `IMvxBundle` provided by the `SaveStateToBundle` method. You can store it using a key-value pair in the bundle's `Data` property.

5. Restore State: When the application resumes, the `ReloadFromBundle` method is called. Here, you can retrieve the stored JSON string from the bundle and deserialize it back into your original object using the `IMvxJsonSerializer`.

Example Implementation

Here's a simplified example of how you might implement this 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);
    }
}

Benefits of JSON Serialization

- Flexibility: JSON serialization allows you to easily save and restore complex data structures.
- Platform Independence: JSON is a widely supported format, making it ideal for cross-platform development.
- Ease of Use: MvvmCross provides built-in support for JSON serialization through its plugins, simplifying the process.

By using JSON serialization with `SaveStateToBundle` and `ReloadFromBundle`, you can effectively manage your ViewModel's state across different application lifecycle events, ensuring a seamless user experience even when the application is suspended or terminated.