MVVM and modality in portable view models

Question

My app (written using MvvmCross and with MVVM pattern in mind) needs to display popup windows where user can choose of confirm certain options. So basically it's a classic modal dialog, but since the app's view model is implemented in a portable class library, it needs to tackle modality in a generalized sense - some platforms simply don't have exact match for a modal dialog.

There are a few threads discussing dialogs in MVVM (Open dialog in WPF MVVM, WPF MVVM dialog example). Following their advices I could probably solve this by introducing DialogService and implementing it for each platform. However I will be treating then dialogs like other services - storage service, map service etc.. But a dialog is a part of the presentation concept, so I wonder if it can be treated more like a view, so instead of calling an instance of an obscure IDialogService I could navigate to it using an MVVM framework of my choice (MvvmCross in my case).

I checked MvvmCross implementation and samples but found almost no dialog-related stuff.

Answer 1

Within MvvmCross, the presenter is responsible for how Views/ViewModels are shown when using ShowViewModel.

This presenter is a view/UI level object - it's ultimately the UIs job to decide if a view should be shown as a page, as a control, in a tab, in a split-view, as a dialog, etc.

v3 does introduce a presentation hint that the ViewModel can help suggest how the View should be shown - but it's up to the presenter on each platform to determine how (if) to use this hint.

---

Alternatively, Dialogs/flyouts/etc can easily be shown using MvxMessenger messages from ViewModel to View with a little bit of code behind.

---

For 'modality', also consider Greg's post on 'returning results' - see http://www.gregshackles.com/2012/11/returning-results-from-view-models-in-mvvmcross/