Simplify injection of ViewModelProvider.Factory instances by using Mu…

…ltibinding.

Adding a ViewModel now only requires adding one method in ViewModelModule and no changes in GithubViewModelFactory.

GithubBrowserSample/app/src/main/java/com/android/example/github/di/AppModule.java

@@ -16,16 +16,14 @@
 
 package com.android.example.github.di;
 
+import android.app.Application;
+import android.arch.persistence.room.Room;
+
 import com.android.example.github.api.GithubService;
 import com.android.example.github.db.GithubDb;
 import com.android.example.github.db.RepoDao;
 import com.android.example.github.db.UserDao;
 import com.android.example.github.util.LiveDataCallAdapterFactory;
-import com.android.example.github.viewmodel.GithubViewModelFactory;
-
-import android.app.Application;
-import android.arch.lifecycle.ViewModelProvider;
-import android.arch.persistence.room.Room;
 
 import javax.inject.Singleton;
 
@@ -34,7 +32,7 @@
 import retrofit2.Retrofit;
 import retrofit2.converter.gson.GsonConverterFactory;
 
-@Module(subcomponents = ViewModelSubComponent.class)
+@Module(includes = ViewModelModule.class)
 class AppModule {
     @Singleton @Provides
     GithubService provideGithubService() {
@@ -60,11 +58,4 @@ UserDao provideUserDao(GithubDb db) {
     RepoDao provideRepoDao(GithubDb db) {
         return db.repoDao();
     }
-
-    @Singleton
-    @Provides
-    ViewModelProvider.Factory provideViewModelFactory(
-            ViewModelSubComponent.Builder viewModelSubComponent) {
-        return new GithubViewModelFactory(viewModelSubComponent.build());
-    }
 }

GithubBrowserSample/app/src/main/java/com/android/example/github/di/ViewModelKey.java

@@ -0,0 +1,19 @@
+package com.android.example.github.di;
+
+import android.arch.lifecycle.ViewModel;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+import dagger.MapKey;
+
+@Documented
+@Target({ElementType.METHOD})
+@Retention(RetentionPolicy.RUNTIME)
+@MapKey
+@interface ViewModelKey {
+    Class<? extends ViewModel> value();
+}

GithubBrowserSample/app/src/main/java/com/android/example/github/di/ViewModelModule.java

@@ -0,0 +1,34 @@
+package com.android.example.github.di;
+
+import android.arch.lifecycle.ViewModel;
+import android.arch.lifecycle.ViewModelProvider;
+
+import com.android.example.github.ui.repo.RepoViewModel;
+import com.android.example.github.ui.search.SearchViewModel;
+import com.android.example.github.ui.user.UserViewModel;
+import com.android.example.github.viewmodel.GithubViewModelFactory;
+
+import dagger.Binds;
+import dagger.Module;
+import dagger.multibindings.IntoMap;
+
+@Module
+abstract class ViewModelModule {
+    @Binds
+    @IntoMap
+    @ViewModelKey(UserViewModel.class)
+    abstract ViewModel bindUserViewModel(UserViewModel userViewModel);
+
+    @Binds
+    @IntoMap
+    @ViewModelKey(SearchViewModel.class)
+    abstract ViewModel bindSearchViewModel(SearchViewModel searchViewModel);
+
+    @Binds
+    @IntoMap
+    @ViewModelKey(RepoViewModel.class)
+    abstract ViewModel bindRepoViewModel(RepoViewModel repoViewModel);
+
+    @Binds
+    abstract ViewModelProvider.Factory bindViewModelFactory(GithubViewModelFactory factory);
+}

GithubBrowserSample/app/src/main/java/com/android/example/github/viewmodel/GithubViewModelFactory.java

@@ -16,42 +16,30 @@
 
 package com.android.example.github.viewmodel;
 
-import com.android.example.github.di.ViewModelSubComponent;
-import com.android.example.github.repository.RepoRepository;
-import com.android.example.github.repository.UserRepository;
-import com.android.example.github.ui.repo.RepoViewModel;
-import com.android.example.github.ui.search.SearchViewModel;
-import com.android.example.github.ui.user.UserViewModel;
-
 import android.arch.lifecycle.ViewModel;
 import android.arch.lifecycle.ViewModelProvider;
-import android.support.v4.util.ArrayMap;
 
 import java.util.Map;
-import java.util.concurrent.Callable;
 
 import javax.inject.Inject;
+import javax.inject.Provider;
 import javax.inject.Singleton;
 
 @Singleton
 public class GithubViewModelFactory implements ViewModelProvider.Factory {
-    private final ArrayMap<Class, Callable<? extends ViewModel>> creators;
+    private final Map<Class<? extends ViewModel>, Provider<ViewModel>> creators;
 
     @Inject
-    public GithubViewModelFactory(ViewModelSubComponent viewModelSubComponent) {
-        creators = new ArrayMap<>();
-        // we cannot inject view models directly because they won't be bound to the owner's
-        // view model scope.
-        creators.put(SearchViewModel.class, () -> viewModelSubComponent.searchViewModel());
-        creators.put(UserViewModel.class, () -> viewModelSubComponent.userViewModel());
-        creators.put(RepoViewModel.class, () -> viewModelSubComponent.repoViewModel());
+    public GithubViewModelFactory(Map<Class<? extends ViewModel>, Provider<ViewModel>> creators) {
+        this.creators = creators;
     }
 
+    @SuppressWarnings("unchecked")
     @Override
     public <T extends ViewModel> T create(Class<T> modelClass) {
-        Callable<? extends ViewModel> creator = creators.get(modelClass);
+        Provider<? extends ViewModel> creator = creators.get(modelClass);
         if (creator == null) {
-            for (Map.Entry<Class, Callable<? extends ViewModel>> entry : creators.entrySet()) {
+            for (Map.Entry<Class<? extends ViewModel>, Provider<ViewModel>> entry : creators.entrySet()) {
                 if (modelClass.isAssignableFrom(entry.getKey())) {
                     creator = entry.getValue();
                     break;
@@ -62,7 +50,7 @@ public <T extends ViewModel> T create(Class<T> modelClass) {
             throw new IllegalArgumentException("unknown model class " + modelClass);
         }
         try {
-            return (T) creator.call();
+            return (T) creator.get();
         } catch (Exception e) {
             throw new RuntimeException(e);
         }