I just start learn ReactiveUI from https://github.com/reactiveui/ReactiveUI.Samples/blob/master/ReactiveUI_4Only.Samples.sln.
I download lastest version via nuget but I cant find class ReactiveAsyncCommand in ReactiveUI.Xaml.
ReactiveAsyncCommand is now in ReactiveUI.Legacy.
来源：https://stackoverflow.com/questions/17792826/reactiveasynccommand-missing-in-reactiveui-5-0-2