I have a MVP app that I want to migrate to MVVM + Jetpack. Using the Navigation Architecture Component (NAC), my setup now is I have a NavHostActivity and its layout file, activity_nav_host.xml houses a DrawerLayout, a Toolbar and a NavigationView:
<?xml version="1.0" encoding="utf-8"?>
<layout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
xmlns:bind="http://schemas.android.com/apk/res-auto">
<data>
<variable
name="vm"
type="com.myapp.base.NavHostViewModel"/>
</data>
<androidx.drawerlayout.widget.DrawerLayout
android:id="@+id/drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:openDrawer="start"
android:fitsSystemWindows="true">
<LinearLayout
android:id="@+id/content"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<include
android:id="@+id/toolbar"
layout="@layout/toolbar_custom"
bind:vm="@{vm}"/>
<fragment
android:id="@+id/fragment_nav_host"
android:name="androidx.navigation.fragment.NavHostFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_below="@id/toolbar"
app:defaultNavHost="true"
app:navGraph="@navigation/graph"/>
</LinearLayout>
<com.google.android.material.navigation.NavigationView
android:id="@+id/nav_drawer"
android:layout_width="360dp"
android:layout_height="match_parent"
android:layout_gravity="start">
<ScrollView
android:id="@+id/scroll_view"
android:layout_width="match_parent"
android:layout_height="match_parent">
<include
android:id="@+id/drawer_navigation"
layout="@layout/drawer_navigation" />
</ScrollView>
</com.google.android.material.navigation.NavigationView>
</androidx.drawerlayout.widget.DrawerLayout>
</layout>
When using the NAC, it's recommended to use one activity and many fragments. In the file above, @+id/fragment_nav_host is the container for those fragments, and for every screen, it's my intention to change the toolbar title accordingly. Here are the contents of the included toolbar (toolbar_custom.xml):
<?xml version="1.0" encoding="utf-8"?>
<layout
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools">
<data>
<variable name="vm" type="com.myapp.base.NavHostViewModel"/>
</data>
<androidx.appcompat.widget.Toolbar
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?android:attr/actionBarSize"
android:paddingEnd="16dp"
android:background="@color/colorPrimary"
app:contentInsetStartWithNavigation="0dp"
android:elevation="4dp">
<RelativeLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="16dp"
android:layout_marginEnd="16dp"
android:background="@android:color/transparent">
<TextView
android:id="@+id/title"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerVertical="true"
android:background="@android:color/transparent"
android:fontFamily="@font/montserrat_bold"
android:textColor="@color/colorPrimaryDark"
android:textSize="20sp"
android:singleLine="true"
android:ellipsize="end"
android:text="@={vm.title}"
tools:text="Title" />
</RelativeLayout>
</androidx.appcompat.widget.Toolbar>
</layout>
And the ViewModel for NavHostActivity:
public class NavHostViewModel extends ViewModel {
public MutableLiveData<String> title = new MutableLiveData<>();
public NavHostViewModel(String title) {
this.title.setValue(title);
}
static class Factory implements ViewModelProvider.Factory {
private String title;
Factory(String title) {
this.title = title;
}
@SuppressWarnings("unchecked")
@NonNull
@Override
public <T extends ViewModel> T create(@NonNull Class<T> modelClass) {
return (T) new NavHostViewModel(title);
}
}
}
Finally, here's NavHostActivity itself:
public class NavHostActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ActivityNavHostBinding binding =
DataBindingUtil.setContentView(this, R.layout.activity_nav_host);
NavHostViewModel viewModel =
ViewModelProviders.of(this, new NavHostViewModel.Factory("MyApp"))
.get(NavHostViewModel.class);
binding.setVm(viewModel);
binding.setLifecycleOwner(this);
}
}
Now, since each fragment screen will have its own title for the toolbar, and the title will come from the ViewModel of that particular fragment, I have that ViewModel extend NavHostViewModel then set the title with a super() call to the parent constructor. An example:
public class DashboardViewModel extends NavHostViewModel {
public DashboardViewModel(String title) {
super(title);
}
static class Factory implements ViewModelProvider.Factory {
private String title;
Factory(String title) {
this.title = title;
}
@SuppressWarnings("unchecked")
@NonNull
@Override
public <T extends ViewModel> T create(@NonNull Class<T> modelClass) {
return (T) new DashboardViewModel(title);
}
}
}
Then instantiating the ViewModel inside its fragment:
public class DashboardView extends Fragment {
@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater,
@Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
DashboardBinding binding = DashboardBinding.inflate(inflater, container, false);
DashboardViewModel viewModel =
ViewModelProviders.of(this, new DashboardViewModel.Factory("Dashboard"))
.get(DashboardViewModel.class);
binding.setVm(viewModel);
binding.setLifecycleOwner(getViewLifecycleOwner());
return binding.getRoot();
}
}
All that doesn't produce what I'm expecting -- the text of the TextView in the toolbar doesn't change, and I'm seeing only the value initially passed when instantiating the NavHostViewModel. No errors are being thrown.
I've had a look and tried this which happens to be the only related question I've found so far that comes closest to my particular problem, but no progress.
Please advise.
