I have a simple application while I'm trying to understand android/room. I would like to have my query from room to be placed into my list view.
PersonDao.class
#Query("Select name from People limit 3")
LiveData<List<String>> getThreeNames();
AvtivityMain.class
private ArrayAdapter<String> adapter;
private PersonDatabase db;
private EditText age;
private EditText name;
Person person;
private DatabaseRepository rDb;
private PersonViewModel personViewModel;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
name = findViewById(R.id.name);
age = findViewById(R.id.age);
adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1);
ListView lvPerson = findViewById(R.id.lv3Poeple);
lvPerson.setAdapter(adapter);
personViewModel = ViewModelProviders.of(this).get(PersonViewModel.class);
}
public void addPerson(View view){
int sAge = Integer.parseInt(age.getText().toString());
String sName = name.getText().toString();
person = new Person(sName, sAge);
personViewModel.insert(person);
System.out.println(personViewModel.getmAllPeople());
System.out.println(personViewModel.getm3People());
//List<String> names = personViewModel.getm3People();
//adapter.add(personViewModel.getm3People());
}
I have commented out the code I am having problems with. I want to be able to use my query from PersonDao and have my list view show 3 names from my Room database.
You need to do a few things, the first is make sure your adapter can take new input. I would suggest creating your own custom one. When you do create it, be sure to include a method that takes your person strings as input and notifies the adapter of the change, like so:
//you need to add an update method to your adapter, so it can change it's data as your
//viewmodel data changes, something like this:
public void setPersons(List<String> personNames) {
//myPersons should be a variable declared within your adapter that the views load info from
myPersons = personNames;
notifyDataSetChanged();
}
Then in your activity you should set the Adapter as a global variable so it can be accessed by multiple methods, such as your view model observer method and it's initial setup in onCreate().
//need to set up adapter variable to access in other methods to keep view model observer
//off the main thread
private ArrayAdapter myAdapter;
After that you can set up the following observer method for your ViewModel (assuming you created the ViewModel Class properly with a return method called getThreeNames() and that isn't just within your DAO as you showed above.
//set up the view model observer to be off the main thread so it isn't tied to your main
//activity lifecyle (which is the whole point/beauty of the ViewModel), you can call this
//method in your onCreate() method and should stay until onDestroy() is called
private void setupPersonViewModel() {
PersonViewModel viewModel
= ViewModelProviders.of(this).get(PersonViewModel.class);
viewModel.getThreeNames().observe(this, new Observer<List<String>>() {
#Override
public void onChanged(#Nullable List<String> persons) {
//so you can see when your app does this in your log
Log.d(TAG, "Updating list of persons from LiveData in ViewModel");
mAdapter.setPersons(persons);
}
});
}
Hope that answers your question. Let me know if you need any further clarification.
Related
Actually, I have a Recyclerview where has a button and(where I get id with position[from RestAPi call])--->>when the button is clicked I set another recylerview..and now I want to the from the first RecyclerviewAdapter.
I have already tried global variable
Here is images enter image description here
From my previous answer from another question i think you need a Singleton Pattern rather than a Global Variable
You simply need a getter that returns the another Adapter's ArrayList<SingleItemModel> but the problem you will face is that you need to have the same instance of the Adapter from the Activity in order to get the populated ArrayList<Model>.
A good workaround is to used Bill Pugh's Singleton in the Adapter
public class Adapter {
private ArrayList<Model> list;
private Adapter() {}
public static Adapter getInstance() {
return InstInit.INSTANCE;
}
// Don't forget to set the list (or NPE)
// because we can't argue with a Singleton
public void setList(ArrayList<Model> list) {
this.list = list;
}
// You can now get the ArrayList
public ArrayList<Model> getList() {
return list;
}
private static class InstInit {
private static final Adapter INSTANCE = new Adapter();
}
// Some codes removed for brevity
// Overrided RecyclerView.Adapter Methods
.................
}
Retrieving the ArrayList assuming that the following Adapters are Singleton
AdapterOne a1 = AdapterOne.getInstance();
AdapterTwo a2 = AdapterTwo.getInstance();
ArrayList<Model> a1RetrievedList = a1.getList();
// You don't need to create a new instance
// creating a new instance doesn't make sense
// because you need to repopulate the list
// for the new instance.
ArrayList<Model> a2RetrievedList = a2.getList();
// You can also retrieve from AdapterTwo
While learning the new android Architecture component’s ViewModel and LiveData, having a little confusion when observe the LiveData changing from database source change, and how this would work with Cursor adapter.
in https://developer.android.com/reference/android/widget/CursorAdapter.html, it says
int FLAG_REGISTER_CONTENT_OBSERVER
If set the adapter will register a content observer on the cursor
and will call onContentChanged() when a notification comes in. Be
careful when using this flag: you will need to unset the current
Cursor from the adapter to avoid leaks due to its registered
observers. This flag is not needed when using a CursorAdapter
with a CursorLoader.
so the with cursorAdaptor it has a way to get the ‘live update’ when the database data is updated.
is there a way to use the LiveData (to observe the database data update) with the cursorAdaptor?
trying to show the question of where to use the liveData updating the cursor in snippet below:
(with the sample of https://codelabs.developers.google.com/codelabs/android-persistence)
the Book:
#Entity
public class Book {
public #PrimaryKey String id;
public String title;
}
The ViewModel:
public class BooksBorrowedByUserViewModel extends AndroidViewModel {
public final LiveData<List<Book>> books;
private AppDatabase mDb;
public BooksBorrowedByUserViewModel(Application application) {
super(application);
createDb();
// Books is a LiveData object so updates are observed.
books = mDb.bookModel().findBooksBorrowedByName("Mike"); //<=== this ViewModel specific to one type query statement
}
public void createDb() {
mDb = AppDatabase.getInMemoryDatabase(this.getApplication());
// Populate it with initial data
DatabaseInitializer.populateAsync(mDb);
}
}
is this the way to use LiveData observer to force reload cursor?
private CursorAdapter listAdapter;
private BooksBorrowedByUserViewModel mViewModel;
private void subscribeUiBooks() {
mViewModel.books.observe(this, new Observer<List<Book>>() {
#Override
public void onChanged(#NonNull final List<Book> books) {
showBooksInUi(books, mBooksTextView); //<== the sample’s code
// if would like to update the cursorAdaptor
//
// ??? to requery the database and swap cursor here?
// Cursor data = queryData(buildSqlStatement()); // build the same sql statement as used in the BooksBorrowedByUserViewModel
// listAdapter.swapCursor(data)
}
});
}
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//having a list using CursorAdaptor
ListView list = getListView();
listAdapter = new CursorAdapter(getActivity(), null, 0)
list.setAdapter(listAdapter);
// Get a reference to the ViewModel for this screen.
mViewModel = ViewModelProviders.of(this).get(BooksBorrowedByUserViewModel.class);
subscribeUiBooks();
}
CursorAdapter is an old stuff, you should use Room + LiveData + RecyclerView.
Your data layer:
public LiveData<List<UserEntity>> getUsers() {
return userDao.getUsers();
}
Your activity:
viewModel.getUsers().observe(this, new Observer<List<UserEntity>>() {
#Override
public void onChanged(#Nullable List<UserEntity> users) {
if (users != null) {
adapter.setUsers(users);
}
}
});
In adapter:
private List<UserEntity> users = new ArrayList<>();
public void setUsers(List<UserEntity> users) {
this.users.clear();
this.users.addAll(users);
notifyDataSetChanged();
}
So when your activity lunch you should get live data from Room and subscribe to it. After that when you add something to that table, room automatically update observers, so you should just setup new data to the adapter and notify it.
Guide to App Architecture
LiveData
Room
currently I am using FirebaseRecyclerAdapter to represent data on a RecyclerView using the following Firebase query:
postsQuery = mDatabase.child("lists_new”).orderByKey().limitToFirst(10);
My RecyclerView has a header with 2 buttons: New List, Old List.
New list is loaded by default, and my question is, when the user taps the Old List button, what is the most efficient way to replace the new list with old list.
The Firebase query for the old list looks like this:
postsQuery = mDatabase.child("lists_old”).orderByKey().limitToFirst(10);
Note: both new list and the old list has the same data types, i.e. they share the same Java POJO class and the the same layout.
You will need a new adapter and attach that to the same RecyclerView.
So after constructing the new query, you create a new adapter and attach it to the view:
adapter = new FirebaseRecyclerAdapter<Chat, ChatHolder>(
Chat.class, android.R.layout.two_line_list_item, ChatHolder.class, postsQuery) {
recyclerView.setAdapter(adapter);
I have a similar need and a similar solution except I am calling cleanup() on the adapter before new'ing up another one. I am thinking without calling cleanup() it will create a leak of adapters and/or listeners?
In onActivityCreated() in my Fragment I am calling a method in the Fragment that manages the recycler view. Call the method to initialize or refresh the list and pass in a leaf node name. If the adapter is not null then call cleanup(). Create a new database reference by concatenating a new leaf node with the parent reference, new-up a new adapter and set it.
I call cleanup() in onDestroy() as well, per usual.
It works fine so far though I've only tested using the emulator and a small data set.
#Override
public void onActivityCreated(#Nullable Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
refreshList(newLeafNode);
}
#Override
public void onDestroy() {
super.onDestroy();
mRVAdapter.cleanup();
}
protected void refreshList(String newLeafNode) {
if (mRVAdapter != null) {
mRVAdapter.cleanup();
}
DatabaseReference newDbRef = mParentRef.child(newLeafNode);
mRVAdapter = new FirebaseRecyclerAdapter<String, MyViewHolder>(String.class, R.layout.single_row, MyViewHolder.class, newDbRef) {
#Override
protected void populateViewHolder(MyViewHolder viewHolder, String model, int position) {
viewHolder.setImage(model);
}
};
mMyRV.setAdapter(mRVAdapter);
}
I am using a singleton for fetching data from a web service and storing the resulting data object in an ArrayList. It looks like this:
public class DataHelper {
private static DataHelper instance = null;
private List<CustomClass> data = null;
protected DataHelper() {
data = new ArrayList<>();
}
public synchronized static DataHelper getInstance() {
if(instance == null) {
instance = new DataHelper();
}
return instance;
}
public void fetchData(){
BackendlessDataQuery query = new BackendlessDataQuery();
QueryOptions options = new QueryOptions();
options.setSortBy(Arrays.asList("street"));
query.setQueryOptions(options);
CustomClass.findAsync(query, new AsyncCallback<BackendlessCollection<CustomClass>>() {
#Override
public void handleResponse(BackendlessCollection<CustomClass> response) {
int size = response.getCurrentPage().size();
if (size > 0) {
addData(response.getData());
response.nextPage(this);
} else {
EventBus.getDefault().post(new FetchedDataEvent(data));
}
}
#Override
public void handleFault(BackendlessFault fault) {
EventBus.getDefault().post(new BackendlessFaultEvent(fault));
}
});
}
public List<CustomClass> getData(){
return this.data;
}
public void setData(List<CustomClass> data){
this.data = data;
}
public void addData(List<Poster> data){
this.data.addAll(data);
}
public List<CustomClass> getData(FilterEnum filter){
if(filter == FilterEnum.NOFILTER){
return getData();
}else{
// Filtering and returning filtered data
}
return getData();
}
}
The data is fetched correctly and the list actually contains data after it. Also, only one instance is created, as intended. However, whenever I call getData later, the length of this.data is 0. Because of this I also tried it with a subclass of Application holding the DataHelper object, resulting in the same problem.
Is there a good way of debugging this? Is there something like global watches in Android Studio?
Is there something wrong with my approach? Is there a better approach? I am mainly an iOS developer, so Android is pretty new to me. I am showing the data from the ArrayList in different views, thus I want to have it present in an the ArrayList as long as the application runs.
Thanks!
EDIT: Example use in a list view fragment (only relevant parts):
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
filter = FilterEnum.NOFILTER;
data = DataHelper.getInstance().getData(filter);
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
customClassListAdapter = new customClassListAdapter(getActivity(), data);}
EDIT2: Added code where I fetch the data from Backendless, changed reference of DataHelper to reference of data in first EDIT
EDIT3: I usa a local EventBus for notifying the list view about the new data. This looks like this and works (initially the data gets populated, but after e.g. applying a filter, the ArrayList I get with getData is empty):
#Subscribe
public void onMessageEvent(FetchedDataEvent event) {
customClassListAdapter.notifyDataSetChanged();
}
Try instead of keeping reference to your DataHelper instance, keeping reference to your list of retrieved items. F.e. when you first fetch the list (and it's ok as you say), assign it to a class member. Or itarate through it and create your own array list of objects for future use.
Okay I finally found the problem. It was not about the object or memory management at all. Since I give the reference on getData to my ArrayAdapter, whenever I call clear (which I do when changing the filter) on the ArrayAdapter, it empties the reference. I basically had to create a copy of the result for the ArrayAdapter:
data = new ArrayList<>(DataHelper.getInstance().getData(filter));
I was not aware of the fact that this is a reference at all. So with this the data always stays in the helper entirely. I only did this because this:
customClassListAdapter.notifyDataSetChanged();
does hot help here, it does not call getData with the new filter again.
Thanks everyone for your contributions, you definitely helped me to debug this.
It is likely that getData does get called before the data is filled.
A simple way to debug this is to add (import android.util.Log) Log.i("MyApp.MyClass.MyMethod", "I am here now"); entries to strategic places in fetchData, addData and getData and then, from the logs displayed by adb logcat ensure the data is filled before getData gets called.
I feel like a broken record.
After many attempts, I have failed at getting a listview through Parse data to display a specific set of information.
Here is my model...this is all data from users:
#ParseClassName("Midwifefirm")
public class Midwifefirm extends ParseObject {
public Midwifefirm() {
// A default constructor is required.
}
//practice name
public String getPracticeName() {
return getString("practicename");
}
public void setPracticeName(String practicename) {
put("practicename", practicename);
}
//education
public String getEducation() {
return getString("education");
}
public void setEducation(String education) {
put("education", education);
}
//years in practice
public String getYearsinPractice() {
return getString("yearsinpractice");
}
public void setYearsinPractice(String yearsinpractice) {
put("yearsinpractice", yearsinpractice);
}
//practice philosophy
public String getPracticePhilosophy() {
return getString("practicephilosophy");
}
public void setPracticePhilosophy(String practicephilosophy) {
put("practicephilosophy", practicephilosophy);
}
I have this adapter; I am wondering what to place in the query section, as I just want to pull the data into the ListView that is defined in the data model:
public class CustomMidwifeAdapter extends ParseQueryAdapter<Midwifefirm> {
public CustomMidwifeAdapter(Context context) {
super(context, new ParseQueryAdapter.QueryFactory<Midwifefirm>() {
public ParseQuery<Midwifefirm> create() {
// Here we can configure a ParseQuery to display
// only top-rated meals.
ParseQuery query = new ParseQuery("Midwives");
return query;
}
});
}
#Override
public View getItemView(Midwifefirm midwifefirm, View view, ViewGroup parent) {
if (view == null) {
view = View.inflate(getContext(), R.layout.activity_midwife_result_list, null);
}
//use midwifefirm as item view/list
super.getItemView(midwifefirm, view, parent);
// find in layout the practice name
TextView titleTextView = (TextView) view.findViewById(R.id.practicename);
//in the midwifefirm data model, call getPracticename
titleTextView.setText(midwifefirm.getString("practicename"));
// Add education view
TextView EducationView = (TextView) view.findViewById(R.id.education);
EducationView.setText(midwifefirm.getString("education"));
// Add yearsexperience view
TextView ExperienceView = (TextView) view.findViewById(R.id.yearsinpractice);
ExperienceView.setText(midwifefirm.getString("yearsinpractice"));
//Add practice philosophy view
TextView PracticePhilosophyView = (TextView) view.findViewById(R.id.practicephilosophy);
PracticePhilosophyView.setText(midwifefirm.getString("practicephilosophy"));
return view;
}
}
And here is the Main Activity:
public class MidwifeResultList extends ListActivity {
private ParseQueryAdapter<ParseObject> mainAdapter;
private CustomMidwifeAdapter midwifeListAdapter;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//initialize main ParseQueryAdapter
mainAdapter = new ParseQueryAdapter<ParseObject>(this, Midwifefirm.class);
//which keys in Midwife object
mainAdapter.setTextKey("practicename");
mainAdapter.setTextKey("education");
mainAdapter.setTextKey("yearsinpractice");
mainAdapter.setTextKey("practicephilosophy");
// Initialize the subclass of ParseQueryAdapter
midwifeListAdapter = new CustomMidwifeAdapter(this);
// Default view is all meals
setListAdapter(mainAdapter);
}
Every time I run this, I get no results.
Thanks in advance for any help
Michael
I can tell you why I think it fails now and I can tell you why I'm very sure it will fail after you sort out the current issue.
It seems that you're trying to use different classes
#ParseClassName("Midwifefirm")
public class Midwifefirm extends ParseObject {
and
ParseQuery query = new ParseQuery("Midwives");
You need to be consistent and use the same name. Either use Midwives or Midwifefirm for both. Let's assume you picked the latter. You're also saying
all that is stored in the user table...wasn't sure if I needed to create new tables.
The query above wants to get all entries of type Midwives. If there's no such type, it'll return nothing. So you have two options:
In you Parse dashboard, reate a class Midwifefirm (don't forget to update the String inside #ParseClassName above) and store your Midwifefirm data in there. You don't need to change your query for this.
Add a column to your ParseUser class, such as type, that you can set to Midwifefirm or whatever if that user is a Midwifefirm or whatever. Then in your query you need to add:
ParseQuery query = new ParseQuery("Midwives");
query.whereEquals("type", "Midwifefirm");
I greatly prefer the former.
Anyway, once your done that, the issue is that you're not using a custom view for this. You're relying on the one provided by Android by default for ListActivity. I am fairly sure it doesn't have any of the fields you're after, so you should create a custom view for this, then at the top of onCreate in your Activity make sure you use it
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.my_custom_view);
By the way, the following are redundant if you populate then in getItemView anyway:
mainAdapter.setTextKey("practicename");
mainAdapter.setTextKey("education");
mainAdapter.setTextKey("yearsinpractice");
mainAdapter.setTextKey("practicephilosophy");
One final advice: if you're still having issues, set breakpoints and do some investigations first. What you need to check is:
Whether you get anything at all from Parse when you do your query. Your adapter has an useful addOnQueryLoadListener that you may use to check whether anything's been retrieved at all.
If stuff is retrieved successfully, you need to check whether the list view is populated correctly. Again, use breakpoints, this time in getItemView maybe.
I'm going to do a wild guess here using the lovely brainwrecking API help of Parse.com about ParseQueryAdapters
Before continuing, may I mind you that my experience with ParseQueryAdapters is a minimum but I think I have a basic knowledge about them + I have some experience with Parse on its own. ANYHOW,
As an example they use both these
final ParseQueryAdapter adapter = new ParseQueryAdapter(this, "Midwives");
adapter.setTextKey("name");
ListView listView = (ListView) findViewById(R.id.listview);
listView.setAdapter(adapter);
and
// Instantiate a QueryFactory to define the ParseQuery to be used for fetching items in this
// Adapter.
ParseQueryAdapter.QueryFactory<ParseObject> factory =
new ParseQueryAdapter.QueryFactory<ParseObject>() {
public ParseQuery create() {
ParseQuery query = new ParseQuery("Midwives");
return query;
}
};
// Pass the factory into the ParseQueryAdapter's constructor.
ParseQueryAdapter<ParseObject> adapter = new ParseQueryAdapter<ParseObject>(this, factory);
adapter.setTextKey("name");
// Perhaps set a callback to be fired upon successful loading of a new set of ParseObjects.
adapter.addOnQueryLoadListener(new OnQueryLoadListener<ParseObject>() {
public void onLoading() {
// Trigger any "loading" UI
}
public void onLoaded(List<ParseObject> objects, ParseException e) {
// Execute any post-loading logic, hide "loading" UI
}
});
// Attach it to your ListView, as in the example above
ListView listView = (ListView) findViewById(R.id.listview);
listView.setAdapter(adapter);
To start of, the reason why I think nothing is loading inside your list has to do with a little mixup between the initilization of your ParseQueryAdapter and your custom adapter.
You configure the basic adapter, and also initialize a custom adapter but you don't do anything with the custom adapter, tho the custom adapter seems to contain the logics to load your data model.
I think what you're looking for is something like this:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//initialize main ParseQueryAdapter
mainAdapter = new CustomMidwifeAdapter<ParseObject>(this);
//which keys in Midwife object
mainAdapter.setTextKey("practicename");
mainAdapter.setTextKey("education");
mainAdapter.setTextKey("yearsinpractice");
mainAdapter.setTextKey("practicephilosophy");
// Default view is all meals
setListAdapter(mainAdapter);
}
All you need to pass is the context (aka "this"), and the constructor of your custom class will handle the factory internal
super(context, new ParseQueryAdapter.QueryFactory<Midwifefirm>() {
public ParseQuery<Midwifefirm> create() {
// Here we can configure a ParseQuery to display
// only top-rated meals.
ParseQuery query = new ParseQuery("Midwives");
return query;
}
});
Tho to be honest since you do:
new ParseQueryAdapter<ParseObject>(this, Midwifefirm.class);
I wonder if you'd need to change your "QueryFactory" to
super(context, new ParseQueryAdapter.QueryFactory<Midwifefirm>() {
public ParseQuery<Midwifefirm> create() {
// Here we can configure a ParseQuery to display
// only top-rated meals.
ParseQuery query = new ParseQuery(MidWifefirm.class);
return query;
}
});
Where you pass a class to the the query rather than the tableName, but I could be wrong on that one.
Either way I hope this has helped in some way!