Uno and WinUI threading¶

The ReactiveUI.Binding.Uno package adds WithUno and UnoBindingModule. The module registers UnoViewThreadInvoker, which moves a write to an Uno control onto the thread that owns it. It targets every Uno Platform head: desktop, WebAssembly, Android, iOS and Windows.

The invoker derives from SequencerViewThreadInvoker<DependencyObject, DispatcherQueueSequencer>, as the Avalonia invoker does:

• Claims accepts any Microsoft.UI.Xaml.DependencyObject, the base class of every Uno control.
• SequencerFor returns DispatcherQueueSequencer.For(target.DispatcherQueue), from the ReactiveUI.Primitives.Uno package. Every dependency object belongs to the dispatcher queue of the thread that created it.
• CheckAccess is true on that queue's thread, and Post queues the write on it.

A generated binding onto an Uno control carries UnoViewThreadInvoker.Instance when your project references the package, so it routes writes even when the module is not registered. It works on every head. On heads other than Windows, Uno declares DependencyObject as an interface that each control implements, and the generator recognises either form. The binding observes the control's dependency properties through RegisterPropertyChangedCallback. The generated fallback explains how. An Unsafe binding uses the registered invokers only, so register the module when you use Unsafe bindings.

WinUI¶

Uno and WinUI share the Microsoft.UI.Xaml.DependencyObject type. A plain WinUI app has no invoker package of its own. The generator does not report RXUIBIND017 for a WinUI binding, and a binding onto a WinUI control writes on the thread that raised the change. To move those writes, register an invoker that derives from SequencerViewThreadInvoker<DependencyObject, DispatcherQueueSequencer>, with DispatcherQueueSequencer from ReactiveUI.Primitives.WinUI, and call ViewThreadInvokers.Refresh.

WinUI and Uno dependency properties raise no PropertyChanged. The generator observes them through their dependency property. Mechanisms covers how.