[Proposal] Add BindingBase support for Bind extension methods to simplify nested bindings

[stephenquan]

CommunityToolkit.Maui.Markup currently provides convenient fluent Bind extension methods for BindableObject, covering many common binding scenarios. However, expressing bindings to nested view model properties remains awkward and error‑prone.
For example, developers currently have two main options:

// String path: simple, but no compile-time safety
CounterBtn.Bind(Button.TextProperty, "NestedObject.NestedCount");

// Compile-time safety, but high complexity and poor ergonomics
CounterBtn.Bind(
    Button.TextProperty,
    getter: static (ViewModel vm) => vm.NestedObject.NestedCount,
    handlers:
    [
        (vm => vm, nameof(ViewModel.NestedObject)),
        (vm => vm.NestedObject, nameof(ViewModel.NestedObject.NestedCount)),
    ]);

While the second approach is type‑safe, the need to manually specify property change handlers for each level of nesting creates a high barrier to entry and discourages usage. This can be significantly simplified by extending Bind to accept a pre‑constructed BindingBase, leveraging the existing BindingBase.Create API, which already handles nested property tracking:

// Proposed BindingBase enhancement
CounterBtn.Bind(
    Button.TextProperty,
    BindingBase.Create(
        static (ViewModel vm) => vm.NestedObject.NestedCount,
        BindingMode.OneWay));

For reference, the view models used in this example are:

public partial class ViewModel
{
    public NestedViewModel NestedObject { get; } = new();
}

public partial class NestedViewModel : ObservableObject
{
    [ObservableProperty]
    public partial int NestedCount { get; set; } = 0;
}

Proposed API

This enhancement can be achieved by adding a single overload to the existing Bind extensions:

public static partial class BindableObjectExtensions
{
    public static TBindable Bind<TBindable>(
        this TBindable bindable,
        BindableProperty targetProperty,
        BindingBase binding)
        where TBindable : BindableObject
    {
        bindable.SetBinding(targetProperty, binding);
        return bindable;
    }
}

GitHub repository

https://github.com/stephenquan/MauiProposedBindOverload

[TheCodeTraveler]

Love it! Let's do it 🙌

[stephenquan]

Tentative commit/diff: main...stephenquan:Maui.Markup:feature/bind-extension