I have a listview of items in my ShoppingListActivity.
Items are added from another activity thought an intent. I want to make sure that all items are kept in the list when going between both activities; however, right now my list only has the last item added from the previous activity.
My ShoppingListActivity.class
public class ShoppingListActivity extends Activity {
private ListView mainListView ;
private ArrayAdapter<String> listAdapter ;
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_shopping_list);
// Find the ListView resource.
mainListView = (ListView) findViewById( R.id.mainListView );
ArrayList<String> shoppingList = new ArrayList<String>();
shoppingList.add(itemLookup());
// Create ArrayAdapter using the shopping list.
listAdapter = new ArrayAdapter<String>(this, R.layout.simplerow, shoppingList);
// Set the ArrayAdapter as the ListView's adapter.
mainListView.setAdapter( listAdapter );
}
//Lookup item by ID
public String itemLookup() {
String itemName = "";
Intent intent = getIntent();
Bundle extras = intent.getExtras();
if (intent != null) {
String itemId = extras.getString("BARCODE_ID");
try {
itemName = ItemLookup.lookupById(itemId);
} catch (IOException e) {
e.printStackTrace();
}
}
return itemName;
}
#Override
public void onBackPressed() {
startActivity(new Intent(ShoppingListActivity.this, MainActivity.class));
}
}
I have a feeling I should be putting my add somewhere else. I'm pretty sure I should be passing the list back and forth in a putExtra, but if that's how I have to do it, it's fine.
How can I make sure that the list is maintained between activities?
One way around your problem is Singleton Pattern.
In your case you can implement something like this:
public class ShoppingListManager {
private static ShoppingListManager instance = new ShoppingListManager();
private List<String> shoppingList;
public static ShoppingListManager getInstance() {
return instance;
}
public List<String> getShoppingList() {
return shoppingList;
}
// Make the constructor private so that this class cannot be instantiated
private ShoppingListManager(){
shoppingList = new ArrayList<String>();
}
}
Then access it anywhere in your code.
ShoppingListManager.getInstance().getShoppingList();
One point to remember never store context in singleton classes as it will lead to memory leaks.
Keeping your data structures in an Activity makes your app prone to data loss because Activities can be destroyed at various times and for a variety of reasons, including rotating the device between portrait and landscape.
You should use a separate class to store and track which items are in the shopping list. The Activity with the ListView should only get the list of items stored and display them. Anything that causes an item to be added should simply trigger a reload of the list (if the Activity is running in the foreground), otherwise the Activity should see that new item anyway the next time it starts.
If you also need your data to be persistent after your process is terminated, you should look into the possible data storage options available.
Related
I have an activity that grabs data via WebService, from there it creates elements to display the data. Some data is grouped so my solution was to display the grouped data in their own fragments below the main layout, allowing the user to swipe across the groups, probably with a tabs at the top to show the group name.
The problem I came across was that the fragments in the activity are created before that web call takes place, making them empty or using old data. I then created a sharedpreferences listener and placed the fragments layout creation method within it. The main method grabs the data, writes to sharedpreferences the fragment detects the change and creates it's layout, Or so I thought.
Some groups are the same between items, so moving from one to the other won't trigger that onchange event thus not triggering the layout creation method. I then decided to do the following to always trigger the onchange event after the sharedpreferences are written
final Boolean updated = settings.getBoolean("UPDATED_1", false);
SharedPreferences.Editor editor = settings.edit();
editor.putBoolean("UPDATED_" + pageNum, !updated);
I just don't think that's the best solution, it also has it's problems and isn't triggering every time (Which I have yet to troubleshoot)
What's a better solution for all this? I also have a memory leak I haven't diagnosed yet to make things even more of a headache.
I've just thought of moving my data grabbing method to before the ViewPager initialization but I'm not yet sure if this will solve my problem.
I would not recommend waiting until you get the data to show the view as it will affect the User Experience and look sluggish.
Instead, you could implement an AsyncTaskLoader in your fragment so you can inform the Fragment's View with a BroadcastReceiver once you get the data from your server. In the meantime, just show a spinner until the data are retrieved, then you hide it and update your list with a adapter.notifyDataSetChanged();.
Here is an example of a AsyncTaskLoader (In my case it's a database query instead of a server call like you):
public class GenericLoader<T extends Comparable<T>> extends AsyncTaskLoader<ArrayList<T>> {
private Class clazz;
public GenericLoader(Context context, Class<T> clazz) {
super(context);
this.clazz = clazz;
}
#Override
public ArrayList<T> loadInBackground() {
ArrayList<T> data = new ArrayList<>();
data.addAll(GenericDAO.getInstance(clazz).queryForAll());
Collections.sort(data);
return data;
}
}
Then in your Fragment:
public class FragmentMobileData extends Fragment implements ListAdapter.OnItemClickListener, LoaderManager.LoaderCallbacks<ArrayList<EntityCategories.EntityCategory>> {
public static String TAG = "FragmentMobileData";
private ImageListAdapter adapter;
private ArrayList<EntityList> mCategories = new ArrayList<>();
private final BroadcastReceiver mReceiver = new BroadcastReceiver() {
#Override
public void onReceive(Context context, Intent intent) {
Bundle bundle = intent.getExtras();
String result = bundle.getString(DatabaseService.RESULT);
if (DatabaseService.NO_CONNECTION.equals(result)) {
Utils.showToastMessage(getActivity(), "No internet connexion", true);
} else if (DatabaseService.RESULT_TIMEOUT.equals(result)) {
Utils.showToastMessage(getActivity(), "Bad connection. Retry", true);
}
getActivity().getSupportLoaderManager().initLoader(1, null, FragmentMobileData.this).forceLoad();
}
};
#Bind(R.id.progressBarEcard)
ProgressBar spinner;
#Bind(R.id.list)
RecyclerView list;
public FragmentMobileData() {
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_mobile_plan, container, false);
ButterKnife.bind(this, view);
((AppCompatActivity) getActivity()).getSupportActionBar().setTitle("Mobile");
list.setLayoutManager(new LinearLayoutManager(context));
list.addItemDecoration(new DividerItemDecoration(context, R.drawable.divider));
adapter = new ImageListAdapter(mCategories, this);
list.setAdapter(adapter);
Intent intent = new Intent(context, DatabaseService.class);
intent.setAction(DatabaseService.UPDATE_DATA);
getActivity().startService(intent);
return view;
}
#Override
public void onPause() {
super.onPause();
getActivity().unregisterReceiver(mReceiver);
}
#Override
public void onResume() {
super.onResume();
getActivity().registerReceiver(mReceiver, new IntentFilter(DatabaseService.UPDATE_DATA));
}
#Override
public Loader<ArrayList<EntityCategories.EntityCategory>> onCreateLoader(int id, Bundle args) {
return new GenericLoader(context, EntityCategories.EntityCategory.class);
}
#Override
public void onLoadFinished(Loader<ArrayList<EntityCategories.EntityCategory>> loader, ArrayList<EntityCategories.EntityCategory> data) {
if (mCategories.size() != data.size()) {
mCategories.clear();
mCategories.addAll(data);
adapter.notifyDataSetChanged();
Intent intent = new Intent(context, DownloadFilesService.class);
context.startService(intent);
}
spinner.setVisibility(View.GONE);
}
#Override
public void onLoaderReset(Loader<ArrayList<EntityCategories.EntityCategory>> loader) {
mCategories.clear();
adapter.notifyDataSetChanged();
}
//...
}
Maybe I misunderstood something. But in your case I think there is pretty good alternative to create, for example, your fragment which will display some group of data, then in it's creation stage show progress bar in ui, and meantime do request to the data in background. Then handle result data and show it, and hide progress bar.
This can be achieved with implementing MVP pattern to provide flexibility of code and easy testing. Also you can use rxJava and Retrofit to handle requests in a convenient way. More information about MVP and samples you can find here.
If you don't want to provide this way for some reason. For example, you have undetermined number of groups, which you will receive in future somehow and you want to dynamically build your fragments base on data which you receive, then I suggest you can organize presentation layer in your activity. In this layer your will receive data then pass it to special handler, which will divide it to groups and base on them will ask activity to create fragment. In constructor you will send already received data (so it is need to implement Parcelable interface).
I have Messanger App that has a Master/Detail Flow Layout with 2 fragments. I used the template provided by Android Studio.
When the ListFragment is in the foreground and a new user logs in the ListView is not immediately updated and the User does not appear on the List.
When I select a different activity and go back to the ListFragment afterwards the list is updated.
this is where my data is stored. If a new user logs in the addUser method is called and this adds the user to the List and Map.
public static List<ChatContent> ITEMS = new ArrayList<ChatContent>();
public static Map<String, ChatContent> ITEM_MAP = new HashMap<String, ChatContent>();
protected static void addUser(ChatContent userChatContent) {
ITEMS.add(userChatContent);
ITEM_MAP.put(userChatContent.user, userChatContent);
}
This is how I set the listAdapter in the onCreate method of the ListFragment.
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ArrayAdapter arrayAdapter = new ArrayAdapter<ChatData.ChatContent>(
getActivity(),
android.R.layout.simple_list_item_activated_1,
android.R.id.text1,
ChatData.ITEMS);
setListAdapter(arrayAdapter);
}
FYI: The same thing happens when I'm on the detailsFragment and a new chat message arrives: the message does not appear unless I leave the activity and come back.
When you update your data ,you should use these code to update the UI.
arrayAdapter.notifyDataSetChanged();
got the following example while reading android book. Can somebody please confirm to me why adapter is always created in this example? Shouldn't it be done only in the case when model == null?
If I understand correctly all data members are retained (in this example), so ListView will be retained, along with its configured ListAdapter and everything else.
public class AsyncDemoFragment extends SherlockListFragment {
private static final String[] items = { "lorem", "ipsum", "dolor" };
private ArrayList<String> model = null;
private ArrayAdapter<String> adapter = null;
#Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
setRetainInstance(true);
if (model == null) {
model = new ArrayList<String>();
new AddStringTask().execute();
}
adapter = new ArrayAdapter<String>(getActivity(), android.R.layout.simple_list_item_1, model);
setListAdapter(adapter);
}
class AddStringTask extends AsyncTask<Void, String, Void> {
// …
protected void onProgressUpdate(String... item) {
adapter.add(item[0]);
}
}
}
The instance of your Fragment will be retained -- however, the View created by the Fragment will still be destroyed and recreated unless specifically retained (which can very easily cause memory leaks). Basically, without setRetainInstance(), the following events (along with others) would happen on a configuration change:
// Fragment initialized
onCreate()
onCreateView()
// Configuration change
onDestroyView()
onDestroy()
onCreate()
onCreateView()
With setRetainInstance(true):
// Fragment initialized
onCreate()
onCreateView()
// Configuration change
onDestroyView()
onCreateView()
Essentially, you still need to recreate the View, but any other instance fields will not be reset.
You should still be able to handle the case where they are reset, however, as even with setRetainInstance(true) your Activity may be killed in the background due to memory pressure.
new to droid programming. im having a small problem that im sure is simply fixed but ive done some searching and a bunch of tutorials but cant seem to find just what i need so i figured id ask. My app has 2 activites, the first activity is just a simple form where a user enters course information(class title, professor..etc.)
the first activity passes the data which is supposed to be stored in a list in the second activity. problem is that only the first course gets stored in the list, after the first time nothing new gets added to the second activity. Can someone point me in the right direction please? thanks in advance
First Activity
public class CourseDetail extends Activity {
//Course c = new Course();
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Button save=(Button)findViewById(R.id.save);
save.setOnClickListener(onSave);
}
private View.OnClickListener onSave=new View.OnClickListener() {
public void onClick(View v) {
EditText course=(EditText)findViewById(R.id.course);
EditText professor=(EditText)findViewById(R.id.professor);
EditText location=(EditText)findViewById(R.id.location);
EditText officehrs=(EditText)findViewById(R.id.officehrs);
Intent i=new Intent(CourseDetail.this, CourseList.class);
i.putExtra("myCourse", course.getText().toString());
i.putExtra("myProfessor", professor.getText().toString());
i.putExtra("myLocation", location.getText().toString());
i.putExtra("myOfficehrs", officehrs.getText().toString());
startActivity(i);
}
};
}
Second Activity
public class CourseList extends Activity {
Button btnCourse;
List<Course> model = new ArrayList<Course>();
CourseAdapter adapter=null;
private String dCourse="";
private String dProfessor="";
private String dLocation="";
private String dOfficehrs="";
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.clist);
ListView list =(ListView)findViewById(R.id.courses);
adapter=new CourseAdapter();
list.setAdapter(adapter);
Course c = new Course();
Bundle extras = getIntent().getExtras();
dCourse = extras !=null ? extras.getString("myCourse") :"no value entered";
dProfessor = extras !=null ? extras.getString("myProfessor") :"no value entered";
dLocation = extras !=null ? extras.getString("myLocation") :"no value entered";
dOfficehrs = extras !=null ? extras.getString("myOfficehrs") :"no value entered";
c.setCourse(dCourse);
c.setProfessor(dProfessor);
c.setLocation(dLocation);
c.setOfficeHrs(dOfficehrs);
btnCourse =(Button)findViewById(R.id.btnCourse);
btnCourse.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
finish();
}
});
}
You are just getting the user entered value in CourseDetail activity and displaying the received value inside the CourseList activity, that means you are not storing these values permanently.
Go through this Android - Data Storage document.
When you move to 2nd activity i.e. CourseList activity, at that time fetch the data from the SQLite table and display the same. whenever you get new values from previous activity, at that time just update the list by adding the new data in ArrayList and make a call on adapter.notifyDataSetChanged()
Some suggestions:
Have your CourseList extend ListActivity instead of just Activity - check out some tutorials on that which should help you set things up correctly.
There seems to be a bit of confusion with how you're handling your lists - you have your model variable but don't seem to be doing anything with it. Again, have a look at a ListView tutorial (just google "android listview tutorial").
You seem to have figured out that you can use "intents" to pass information from one activity to another, but since you're only doing this in the onCreate() method, it's only happening once. Try doing this in your ListActivity's adapter once for each item.
Don't give up on Android, keep trying :-)
Some suggestion:
You have to add your object to the adapter: adapter.add(c); after you get the data.
Call adapter.notifyDataSetChanged() to notify the system that your data for the listView has been changed. Call list.invalidate() to refresh it.
I noticed that you set the button with the finish() method. Hmm, if you do so, the next time you get to CourseList Activity from CourseDetail, the adapter will be null again. No previously received data will be available. Is this what you really want?
The problem is you are not adding the newly added items to the List.So before setting adapter you have to add all your objects like
list.add(c);
In my application, after enough clicking around, I get this error:
06-08 19:47:59.967: ERROR/AndroidRuntime(2429): java.lang.RuntimeException: Unable to pause activity {com.MYAPP.app/com.MYAPP.app.MainActivity}: android.database.StaleDataException: Access closed cursor
What I have is a Tab Activity (my MainActivity), which has a ListActivity as the contents for each tab. Inside the onCreate for each ListActivity I get a cursor that represents the data to be displayed in that list.
The onListItemClick for each list also creates another activity, so clicking on an item in the list will show more information about that item in a new screen. It's inconsistent, but after enough clicking into these new activities, or going back to the ListView from a new activity, the program crashes.
In searching around for a solution to my problem, I did stumble upon registerDataSetObserver, but it doesn't seem to be the whole answer. I am also having trouble finding documentation on it, so I'm not sure I fully understand it. I have a custom ListAdapter that both my ListViews use and have called registerDataSetObservers on the cursors there.
I have attached the relevant code from one of my ListActivities and from my custom ListAdapter class.
The ListActivity. I have two of these, almost identical, except they both have different cursors created from different database queries:
import com.MYAPP.app.listmanager.DeviceListAdapter;
public class AllSensorsActivity extends ListActivity{
private DeviceListAdapter AllList;
private DbManager db;
protected Cursor AllCur;
protected Cursor AllSensors;
private static final String TAG = "AllSensorsActivity";
#Override
public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
Log.e(TAG, "Calling All onCreate");
db = new DbManager(this);
db.open();
AllCur = db.fetchAllDevices();
startManagingCursor(AllCur);
AllSensors = db.fetchAllSensors();
startManagingCursor(AllSensors);
AllList = new DeviceListAdapter(this, AllCur, AllSensors);
setListAdapter(AllList);
}
#Override
protected void onListItemClick(ListView l, View v, int position, long id){
String device_name = (String) ((DeviceListAdapter)getListAdapter()).getItem(position);
String sensor_string = ((DeviceListAdapter)getListAdapter()).getSensors(id);
Intent i = new Intent(this, SensorActivity.class);
Bundle bundle = new Bundle();
bundle.putString("NAME", device_name);
i.putExtras(bundle);
bundle.putString("SENSORS", sensor_string);
i.putExtras(bundle);
this.startActivity(i);
}
The custom ListAdapter:
public class DeviceListAdapter extends BaseAdapter {
private static final String TAG = "DeviceListAdapter";
private Context mContext;
private Cursor mSensors;
private Cursor mDevices;
protected MyDataSetObserver sensors_observer;
protected MyDataSetObserver devices_observer;
public DeviceListAdapter(Context context, Cursor devices, Cursor sensors){
mContext = context;
mDevices = devices;
mSensors = sensors;
sensors_observer = new MyDataSetObserver();
mSensors.registerDataSetObserver(sensors_observer);
devices_observer = new MyDataSetObserver();
mDevices.registerDataSetObserver(devices_observer);
}
// ... more functions and stuff that are not relevant go down here...
}
private class MyDataSetObserver extends DataSetObserver {
public void onChanged(){
Log.e(TAG, "CHANGED CURSOR!");
}
public void onInvalidated(){
Log.e(TAG, "INVALIDATED CURSOR!");
}
}
Should I just have MyDataSetObserver catch the exception and move on? I'd like a more robust solution than that if possible. Or is there some other way I could rearrange my program so that the staleDataException doesn't occur (as often)? I believe that it is happening because I am launching the new activity in my onListItemClick.
I believe when it's invalidated you want to call requery() on the cursor. You could possibly do that in onInvalidated().