I am using ReactiveUI in Windows Forms project and want to bind a view model property to a tool strip menu item checked property. The ToolStripMenuItem control is not bindable and there is no built in support for this control in ReactiveUI.

A simple two way bind will not work since the control will not notify about property changes:

this.Bind(ViewModel, vm => vm.ReuseAddresses, view => view.ReuseAddresses.Checked);

ReactiveUI to the rescue! There is an overload method that will allow you to pass an observable (of any type) that will trigger an update of the view model property:

this.Bind(ViewModel, vm => vm.ReuseAddresses, view => view.ReuseAddresses.Checked, ReuseAddresses.CheckedObservable());

I made a simple extension method on ToolStripMenuItem that returns an observable for the CheckedChanged event like this:

public static IObservable<bool>  CheckedObservable(this ToolStripMenuItem self)
{
    var observable = Observable
        .FromEventPattern(
            h => self.CheckedChanged += h,
            h => self.CheckedChanged -= h
            )
        .Select(e => ((ToolStripMenuItem)e.Sender).Checked);

    return observable;
}

There is a NuGet package ReactiveUI.Events that adds lots of extension methods for events in WPF. But for Windows Forms you are stuck with creating your own, at least for now.