java - Are actions allowed in MVVM? Android -

if mvvm data binding , cannot view.dothis(), otherwise it's mvp, how invoke actions on views?

suppose have view has snackbar. view controlled viewmodel. how viewmodel supposed show snackbar without going snackbar.show()?

in mvvm, viewmodel captures state of view. view observes viewmodel changes , updates itself. thus, communication between view & viewmodel happens through change of values (as against method calls in mvp).

since snackbar global behaviour (like toast), can implemented @ activity/fragment level. so, can make messagehelper interface , pass viewmodel dependency. activity implement , display snackbar.

example:

• itemviewmodel consumes interface
• activity base class implements interface

however, possible there view specific behaviour cannot implemented @ activity level. such cases, can make use of databinding.observable trigger event. example, lets want animate particular view. can create bindingadapter

@bindingadapter({"shaketrigger"}) public static void showsnackbar(view view, void trigger) {     // animation here. add meaningful argument types control animation } 

in xml, can apply using

    <textview         bind:shaketrigger="@{vm.shaketrigger}"/> 

then, in viewmodel, can trigger shake using data binding apis. 1 way using baseobservable can be:

public class configurationviewmodel extends baseobservable implements viewmodel {     @bindable     public final void shaketrigger = null;      public void shake() {         notifypropertychanged(br.shaketrigger);     } } 

if use rxjava, trigger implemented rx.observable. can checkout library use rxjava data binding. https://github.com/manas-chaudhari/android-mvvm