How do I handle parameter serialization in MvvmCross

Understanding MvvmCross Serialization

MvvmCross serializes navigation parameters using JSON. This means that any object passed as a parameter to `ShowViewModel` will be converted into a JSON string and then deserialized when received by the target view model's `Init` method. For simple types like integers and strings, this process is straightforward and requires no additional configuration.

Handling Complex Types

When passing complex types, such as custom classes, you might encounter issues if the serialization and deserialization process fails. This can happen if the complex type contains reference types or nested objects that JSON.NET (the serializer used by MvvmCross) cannot handle by default.

To handle complex types effectively:

1. Implement Custom Serialization: You can create custom converters for your complex types by implementing `IMvxJsonConverter`. This allows you to define how your complex objects should be serialized and deserialized.

2. Use MvxJsonNavigationSerializer: Ensure that `MvxJsonNavigationSerializer` is properly configured. This serializer is specifically designed for navigation parameters and can handle more complex scenarios than the standard JSON serializer.

3. BaseViewModel Approach: Another approach is to create a base view model that handles serialization and deserialization manually. This involves serializing the parameter before passing it to `ShowViewModel` and then deserializing it in the target view model's `Init` method.

Implementing Custom Serialization

To implement custom serialization for complex types, you can follow these steps:

- Define a Custom Converter: Create a class that implements `IMvxJsonConverter`. This class will define how your complex type is serialized and deserialized.

- Register the Converter: Register your custom converter with MvvmCross. This ensures that your converter is used when serializing and deserializing your complex type.

Example of Custom Serialization

Here's an example of how you might implement custom serialization for a complex type:

csharp
public class ComplexTypeConverter : IMvxJsonConverter
{
    public bool CanConvert(Type objectType)
    {
        return objectType == typeof(ComplexType);
    }

    public object Deserialize(string json, Type type)
    {
        // Implement deserialization logic here
        return JsonConvert.DeserializeObject(json);
    }

    public string Serialize(object obj, Type type)
    {
        // Implement serialization logic here
        return JsonConvert.SerializeObject(obj);
    }
}

// Register the converter
protected override void FillValueConverters(IMvxValueConverterRegistry registry)
{
    base.FillValueConverters(registry);
    registry.AddOrOverwrite(typeof(ComplexType), new ComplexTypeConverter());
}

Using BaseViewModel for Serialization

If you prefer not to implement custom converters, you can handle serialization and deserialization manually within your view models. Here's how you might do it:

csharp
public class BaseViewModel : MvxViewModel
{
    protected void ShowViewModel(object parameter) where TViewModel : IMvxViewModel
    {
        var serializedParameter = JsonConvert.SerializeObject(parameter);
        base.ShowViewModel(serializedParameter);
    }
}

public class TargetViewModel : MvxViewModel
{
    public void Init(string parameter)
    {
        if (!string.IsNullOrEmpty(parameter))
        {
            var deserializedParameter = JsonConvert.DeserializeObject(parameter);
            // Use the deserialized parameter
        }
    }
}

Conclusion

Handling parameter serialization in MvvmCross involves understanding how JSON serialization works and implementing custom solutions for complex types. By using custom converters or manual serialization within view models, you can ensure that your complex parameters are properly passed between view models.