add ListAllChatPostsViewModel #5

Author: VeeShostak

app/src/main/java/io/github/veeshostak/aichat/database/AppDatabase.java

@@ -13,15 +13,15 @@
  */
 
 @Database(entities = {ChatPost.class}, version = 1)
-public abstract class ChatPostDatabase extends RoomDatabase {
+public abstract class AppDatabase extends RoomDatabase {
  // create Db and get an instance of it
- private static ChatPostDatabase INSTANCE;
+ private static AppDatabase INSTANCE;
 
- public static ChatPostDatabase getDatabase(Context context) {
+ public static AppDatabase getDatabase(Context context) {
  if (INSTANCE == null) {
  INSTANCE =
  Room.databaseBuilder(context.getApplicationContext(),
- ChatPostDatabase.class, "user-chat-posts")
+ AppDatabase.class, "user-chat-posts")
  .build();
  }
  return INSTANCE;

app/src/main/java/io/github/veeshostak/aichat/viewmodels/ListAllChatPostsViewModel.java

@@ -0,0 +1,70 @@
+package io.github.veeshostak.aichat.viewmodels;
+
+import android.app.Application;
+import android.arch.lifecycle.AndroidViewModel;
+import android.arch.lifecycle.LiveData;
+import android.os.AsyncTask;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import io.github.veeshostak.aichat.database.AppDatabase;
+import io.github.veeshostak.aichat.database.dao.ChatPostDao;
+import io.github.veeshostak.aichat.database.entity.ChatPost;
+
+/**
+ * Created by vladshostak on 12/26/17.
+ */
+
+/*
+
+ViewModels do not contain code related to the UI. This helps in the decoupling of our app components.
+In Room, the database instance should ideally be contained in a ViewModel rather than on the Activity/Fragment.
+
+ViewModels are entities that are free of the Activity/Fragment lifecycle.
+For example, they can retain their state/data even during an orientation change.
+*/
+
+// If your ViewModel needs the application context, it must extend AndroidViewModel, else extend ViewModel
+public class ListAllChatPostsViewModel extends AndroidViewModel {
+
+ private LiveData<List<ChatPost>> chatPostList;
+
+ private AppDatabase appDatabase;
+
+ public ListAllChatPostsViewModel(Application application) {
+ super(application);
+ // get instance of our db
+ appDatabase = AppDatabase.getDatabase(this.getApplication());
+ // Set ChatPosts. Live Data runs the query asynchronously on a background thread
+ chatPostList = appDatabase.chatPostDao().getAllChatPosts();
+ }
+
+ // Get chatPosts. Live Data runs the query asynchronously on a background thread
+ public LiveData<List<ChatPost>> getData() {
+ if (chatPostList == null) {
+ chatPostList = appDatabase.chatPostDao().getAllChatPosts();
+ }
+ return chatPostList;
+ }
+
+
+ // delete doesnt use liveData, execute in another thread. (Live Data runs the query asynchronously on a background thread when needed)
+ public void deleteItem(ChatPost toDeleteChatPost) {
+ new DeleteAsyncTask(appDatabase).execute(toDeleteChatPost);
+ }
+ private static class DeleteAsyncTask extends AsyncTask<ChatPost, Void, Void> {
+ private AppDatabase appDb;
+ DeleteAsyncTask(AppDatabase appDatabase) {
+ appDb = appDatabase;
+ }
+ @Override
+ protected Void doInBackground(final ChatPost... params) {
+ appDb.chatPostDao().deleteChatPosts(params[0]);
+ return null;
+ }
+ }
+
+
+}
+