Are there any specific libraries or tools needed for two-way binding in MvvmCross

MvvmCross Built-in Support

MvvmCross supports two-way binding by default for many controls, which means you typically don't need additional libraries for standard scenarios. The framework mirrors the data binding structure found in Microsoft's XAML-based frameworks but extends it for cross-platform use[4][9].

Custom Views and Controls

For custom views or controls like `UITextView`, which do not inherently support two-way binding, you need to implement custom bindings. This involves creating a `TargetBinding` class that specifies how to bind the custom view's property and which event to listen for changes[7].

Here's a general approach for implementing two-way binding for a custom view:

1. Create a Custom Target Binding Class: You need to subclass `MvxTargetBinding` and implement the necessary methods to handle setting the value and subscribing to events that indicate changes in the view.

2. Subscribe to Events: For controls like `UITextView`, you would typically subscribe to events like `TextChanged` to capture changes and notify the binding engine.

3. Register the Custom Binding: You must register your custom binding in the MvvmCross setup so that it can be used throughout your application.

Example for UITextView

For `UITextView`, you might implement a custom binding by listening to the `TextChanged` event. Here's a simplified example of how you might structure this:

csharp
public class UITextViewBinding : MvxConvertingTargetBinding
{
    private UITextView _textView;

    public UITextViewBinding(UITextView textView) : base(textView)
    {
        _textView = textView;
        _textView.TextChanged += OnTextChanged;
    }

    private void OnTextChanged(object sender, EventArgs e)
    {
        FireValueChanged();
    }

    public override void SetValue(object value)
    {
        _textView.Text = (string)value;
    }

    protected override void Dispose(bool isDisposing)
    {
        if (isDisposing)
        {
            _textView.TextChanged -= OnTextChanged;
        }
        base.Dispose(isDisposing);
    }
}

Then, you would need to register this binding in your MvvmCross setup:

csharp
protected override void FillTargetFactories(IMvxTargetBindingFactoryRegistry registry)
{
    registry.RegisterCustomBindingFactory("Text", textView => new UITextViewBinding(textView));
}

Tools and Libraries

While MvvmCross itself provides the necessary infrastructure for two-way binding, you might need additional tools or libraries for specific scenarios, such as converters or custom view bindings. However, these are typically developed as part of your application rather than being external dependencies.

In summary, MvvmCross supports two-way binding natively for many controls, but for custom views like `UITextView`, you need to create custom bindings. This process involves implementing a `TargetBinding` class and registering it with MvvmCross.