Can I use custom bindings across different platforms in MvvmCross

Custom Bindings in MvvmCross

To create custom bindings in MvvmCross, you typically need to write a `TargetBinding` class. This class describes how to bind a specific property and, in the case of two-way bindings, which event to listen to for value changes[1]. MvvmCross provides several base classes for target bindings, such as `MvxTargetBinding`, `MvxConvertingTargetBinding`, `MvxPropertyInfoTargetBinding`, and `MvxWithEventPropertyInfoTargetBinding`, each serving different purposes and simplifying the process of creating custom bindings[1].

Platform-Specific Considerations

While MvvmCross allows you to define custom bindings in a platform-agnostic way, the implementation details might vary slightly across platforms due to differences in UI components and event handling mechanisms. For example, on iOS and Android, you might need to handle events differently compared to Windows or Xamarin.Forms, where `DependencyProperty` or `BindableProperty` is used[1].

Creating Custom Bindings

1. Define the TargetBinding Class: Create a class that inherits from `MvxTargetBinding` or one of its subclasses. This class should implement the `SetValue` method to set the value on the target view and subscribe to events to notify the binding engine of changes.

2. Register the Binding: Register your custom target binding with MvvmCross so that it can be used in binding expressions.

3. Use Fluent Bindings or XML Bindings: Once your custom binding is defined and registered, you can use it in your views either through fluent bindings in code-behind or through XML bindings using the `MvxBind` attribute on Android or XAML bindings on other platforms[2][3].

Example of Creating a Custom Binding

Here's a simplified example of creating a custom binding for a hypothetical `MyView` with a `MyProperty`:

csharp
public class MyViewTargetBinding : MvxConvertingTargetBinding
{
    public MyViewTargetBinding(MyView target) 
        : base(target)
    {
    }

    public override void SetValue(object value)
    {
        var view = (MyView)Target;
        view.MyProperty = (string)value; // Assuming MyProperty is a string
    }

    public override Type TargetType => typeof(MyView);
    public override MvxBindingMode DefaultMode => MvxBindingMode.OneWay;

    protected override void SubscribeToEvents()
    {
        var view = (MyView)Target;
        view.MyPropertyChanged += View_MyPropertyChanged;
    }

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

    protected override void Dispose(bool isDisposing)
    {
        base.Dispose(isDisposing);
        if (isDisposing)
        {
            var view = (MyView)Target;
            view.MyPropertyChanged -= View_MyPropertyChanged;
        }
    }
}

You would then need to register this binding in your setup:

csharp
protected override void FillTargetFactories(IMvxTargetBindingFactoryRegistry registry)
{
    registry.RegisterCustomBindingFactory("MyProperty", view => new MyViewTargetBinding(view));
}

This allows you to bind `MyProperty` of `MyView` to a property in your ViewModel using MvvmCross's binding expressions.

Conclusion

MvvmCross provides a robust framework for creating custom bindings across different platforms, allowing developers to extend its functionality and support custom views and properties. By leveraging its flexible binding engine and platform-specific features, you can create powerful cross-platform applications with a consistent MVVM architecture.