这个周末，在两场史诗般的战斗之外，我还有一个悲剧。我正在尝试为我的投资组合创建一个健身追踪应用。
在该应用程序中，一切似乎都很好-AndroidStudios的模拟器清楚地显示了RecyclerView元素（我将深色背景和奇怪的边距设置为清晰可见）。并且数据库似乎正在正确填充。但是不会出现任何内容填充RecyclerView。在这一点上，我只是试图让他们阅读“你好”，但他们最终将需要存储客户端数据。 （为了简化问题，尝试从后一种情况切换到前一种情况时，我可能会感到困惑。）
AdminListActivity
public class AdminListActivity extends AppCompatActivity {
public static final int NEW_USER_ACTIVITY_REQUEST_CODE = 1;
private ViewModel mViewModel;
private List<User> mUsers;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.fragment_admin_list);
RecyclerView recyclerView = findViewById(R.id.admin_recycler_view);
final UserListAdapter adapter = new UserListAdapter(this, mUsers);
recyclerView.setAdapter(adapter);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
// Get ViewModel from ViewModelProvider
mViewModel = ViewModelProviders.of(this).get(ViewModel.class);
// Observer on LiveData returned by getAllUsers.
mViewModel.getAllUsers().observe(this, new Observer<List<User>>() {
@Override
public void onChanged(@Nullable final List<User> users) {
// Update the cached copy of the words in the adapter.
adapter.setUsers(users);
}
});
}
public void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if (requestCode == NEW_USER_ACTIVITY_REQUEST_CODE && resultCode == RESULT_OK) {
User user = new User(data.getStringExtra(RegisterFragment.EXTRA_REPLY));
mViewModel.addUser(user);
} else {
Toast.makeText(
getApplicationContext(),
"not saved",
Toast.LENGTH_LONG).show();
}
}
}
AdminListFragment
public class AdminListFragment extends Fragment implements View.OnClickListener {
private RecyclerView mUserRecyclerView;
private Button mAddNewClient;
public AdminListFragment() {}
@Override
public void onClick(View v) {
// required onClick method
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setHasOptionsMenu(true);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_admin_list, container, false);
mUserRecyclerView = (RecyclerView) view.findViewById(R.id.admin_recycler_view);
mUserRecyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
setHasOptionsMenu(true);
mAddNewClient = view.findViewById(R.id.add_new_client);
return view;
}
@Override
public void onResume() {
super.onResume();
}
@Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
}
@Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
super.onCreateOptionsMenu(menu, inflater);
menu.clear();
inflater.inflate(R.menu.fragment_admin_list, menu);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.add_new_client: SingleFragmentActivity.fm.beginTransaction().replace(R.id.fragment_container,
new RegisterFragment()).addToBackStack(null).commit();
// TODO: OR: add from contacts
return true;
default:
return super.onOptionsItemSelected(item);
}
}
}
UserListAdapter
public class UserListAdapter extends RecyclerView.Adapter<UserListAdapter.UserViewHolder> {
private LayoutInflater mInflater = null;
private List<User> mUsers = Collections.emptyList(); // Cached copy of users
public UserListAdapter(Context context, List<User> mUsers) {
mInflater = LayoutInflater.from(context);
}
void setUsers(List<User> users) {
mUsers = users;
notifyDataSetChanged();
}
class UserViewHolder extends RecyclerView.ViewHolder {
private TextView userListItem;
public UserViewHolder(View itemView) {
super(itemView);
userListItem = itemView.findViewById(R.id.userListItem);
}
}
@Override
public UserViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View itemView = mInflater.inflate(R.layout.recyclyerview_user_list_item, parent, false);
return new UserViewHolder(itemView);
}
@Override
public void onBindViewHolder(UserViewHolder holder, int position) {
User current = mUsers.get(position);
holder.userListItem.setText(current.getClientName());
}
// getItemCount() is called many times, and when it is first called,
// mUsers has not been updated (means initially, it's null, and we can't return null).
@Override
public int getItemCount() {
return mUsers.size();
}
}
ViewModel
public class ViewModel extends AndroidViewModel {
private UserDao mUserDao;
public Repository mRepository;
public LiveData<List<User>> mAllUsers;
public ViewModel (Application application) {
super(application);
mRepository = new Repository(application);
mAllUsers = mRepository.getAllUsers();
}
public LiveData<List<User>> getAllUsers() { return mAllUsers; }
public void addUser(User user) { mRepository.addUser(user); }
}
存储库
public class Repository {
private UserDao mUserDao;
private LiveData<List<User>> mAllUsers;
public Repository(Application application) {
UserDatabase db = UserDatabase.buildDatabase(application);
mUserDao = db.userDao();
mAllUsers = mUserDao.getAllUsers();
}
public LiveData<List<User>> getAllUsers() {
return mAllUsers;
}
public void addUser(User user) {
new insertAsyncTask(mUserDao).execute(user);
}
private static class insertAsyncTask extends AsyncTask<User, Void, Void> {
private UserDao mAsyncTaskDao;
insertAsyncTask(UserDao dao) {
mAsyncTaskDao = dao;
}
@Override
protected Void doInBackground(final User... params) {
mAsyncTaskDao.addUser(params[0]);
return null;
}
}
}
列表项的XML：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<TextView
android:id="@+id/userListItem"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="300dp"
android:text="HELLO"
android:textColor="#000000"
android:visibility="visible"
tools:visibility="visible" />
</LinearLayout>
片段中用于recyclerview的XML：
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
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"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="admin.AdminListFragment">
<androidx.recyclerview.widget.RecyclerView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/admin_recycler_view"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:layout_marginEnd="8dp"
android:layout_marginBottom="8dp"
android:background="@android:color/darker_gray"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
tools:listitem="@layout/recyclyerview_user_list_item" />
</androidx.constraintlayout.widget.ConstraintLayout>
UserDatabase
@Database(entities = {User.class, Admin.class}, version = 6, exportSchema = false)
public abstract class UserDatabase extends RoomDatabase {
private static volatile UserDatabase INSTANCE;
public abstract UserDao userDao();
public static final String SP_NAME = "users";
public static UserDatabase buildDatabase(final Context context) {
if (INSTANCE == null) {
synchronized (UserDatabase.class) {
if (INSTANCE == null) {
INSTANCE = Room.databaseBuilder(context.getApplicationContext(), UserDatabase.class, "users").build();
}
}
}
return INSTANCE;
}
/**
* Override the onOpen method to populate the database.
* For this sample, we clear the database every time it is created or opened.
*
* If you want to populate the database only when the database is created for the 1st time,
* override RoomDatabase.Callback()#onCreate
*/
private static RoomDatabase.Callback sRoomDatabaseCallback = new RoomDatabase.Callback() {
@Override
public void onOpen(@NonNull SupportSQLiteDatabase db) {
super.onOpen(db);
// If you want to keep the data through app restarts,
// comment out the following line.
new PopulateDbAsync(INSTANCE).execute();
}
};
/**
* Populate the database in the background.
* If you want to start with more words, just add them.
*/
private static class PopulateDbAsync extends AsyncTask<Void, Void, Void> {
private final UserDao mDao;
PopulateDbAsync(UserDatabase db) {
mDao = db.userDao();
}
@Override
protected Void doInBackground(final Void... params) {
// Start the app with a clean database every time.
// Not needed if you only populate on creation.
//mDao.deleteAll();
User user = new User("Dickon", "d");
mDao.addUser(user);
user = new User("Pumpy", "d");
mDao.addUser(user);
return null;
}
}
}
UserDao
package database;
import java.util.List;
import androidx.lifecycle.LiveData;
import androidx.room.Dao;
import androidx.room.Delete;
import androidx.room.Insert;
import androidx.room.Query;
import User.User;
import admin.Admin;
@Dao
public interface UserDao {
@Insert
void addUser(User user);
@Insert
void createAdmin(Admin admin);
@Query("select * from users")
LiveData<List<User>> getUser();
@Query
("SELECT * from users ORDER BY clientName")
LiveData<List<User>> getAllUsers();
@Query("select * FROM users WHERE id = :id")
List<User> getUserById(int id);
@Query("select * FROM users WHERE clientName = :clientName LIMIT 1")
List<User> getUserByName(String clientName);
@Delete
void DeleteUser(User user);
}
答案 0 :(得分：0)
您在AdminListActivity中拥有
setContentView(R.layout.fragment_admin_list);
RecyclerView recyclerView = findViewById(R.id.admin_recycler_view);
final UserListAdapter adapter = new UserListAdapter(this, mUsers);
recyclerView.setAdapter(adapter);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
在您的AdminListFragment中
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_admin_list, container, false);
mUserRecyclerView = (RecyclerView) view.findViewById(R.id.admin_recycler_view);
mUserRecyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
...
}
片段中的recyclerView与活动中的recyclerView不同。因此，您可以在“活动”中看到用户，但在片段中看不到。
您的片段recyclerView没有适配器。