Say I have a List<User>. Now I can wrap this list in an ArrayAdapter.
List<User> users = Users.getAll();
ArrayAdapter<User> = new ArrayAdapter<User>(this, android.R.layout.simple_list_item_1, users);
I then bind the adapter to a listview to display the list of Users.
Users.getAll() uses Sugar ORM to query the database and return a list of users. Items can be added to the user list from the activity that displays the user list. I am wondering how do I keep the listview updated.
Option 1
One way is to manually update the users as a I add to the database and then call adapter.notifyDataSetChanged(). This works, but it doesn't feel right because I am maintaining a "fake" list that represents what is in the database.
Option 2
I am wondering how bad is it if I just clear the items in users, update it with the results of a new database query and then call adapter.notifyDataSetChanged()?
Will all the child views be thrown away and be re-rendered? Or does it call the equals() method to see if the models bound to each child is the same and then update only what is new?
Other Info
Since I am using SugarORM, I don't think I can get access to the Cursor to do something more efficient. However if there is a better way to keep the list synced with SugarORM, I am happy to hear that as well.
In answer to your option 2: No, it doesnt call equals, because the adapter works in conjunction with the widget to re-use the views, it doens't create a new view foreach item in the list, it create a view foreach visible item and as you scroll re-uses view that left the screen.
The best option here is to create your own adapter, creating a class extending BaseAdapter and creating your own logic inside it requerying the database and notifying the change to the listview (or gridview)..
On the other hand doing what you said here:
I am wondering how bad is it if I just clear the items in users, update it with the results of a new database query and then call adapter.notifyDataSetChanged()?
isn't bad either.
Create a DAO class that extends Observable, then have your Adapter implement Observer. Now every time you add or remove a SugarRecord, do through the DAO class and whoever is register as the Observer will get notified through the following method:
#Override
public void update(Observable observable, Object o)
You can more about Observable/Observer pattern here. This is just one of the many examples and tutorials out there.
Related
I am doing a side project of making an app (with Java since I already know it). I have a recyclerview which loads some data via the room database library. The elements of the recyclerview are clickable.
My problem is I want the user to be able to sort the recyclerview so that the most recently accessed items go to the top.
My original idea was to assign the entities to have two variables - a String list_name which also serves as the id, and an Int order_of_access. Also, in my ViewModel I have a getAllLists method which returns a livedata list. I have an onChanged listener in the fragment activity which nicely updates the recyclerview when data is added/removed.
When the user adds a new list, it is assigned an order_of_access of the listsize (+1). But when the user deletes a group of lists, or clicks on a list, I want to update the order_of_access, say with an updateOrderAccess method.
Do you think this is the best way of doing what I want?
Where should I place updateOrderAccess and how would you recommend it be written? Since the method getAllLists returns livedata, it is tempting to put updateOrderAccess in an observer in the fragment (in onChanged) - but this will obviously create an infinite loop. It seems more in the correct philosophy to put it in the ViewModel, but then how would you suggest the updateOrderAccess method to be written? I'm having some trouble conceptualising what I need.
I hope the question is not too vague - I will update it if you need more details.
Where should I place updateOrderAccess and how would you recommend it
be written?
I am so sure that you must write it in the view model, as long as updateOrderAccess() is editing the list which is observable then you have andexpose by that the ui state then you have to put it in view model, and the observers will be notified ( in this case it is recycle view) and it will redraw the list in the order you offered.
note: do not you ever update the state(ui data) outside the state holder so you implement UDF (unidirectional Data Flow) pattern.
see the references below to read more about UDF so you never get confused where to declare your functions by letting the architicture lead you:
Guide to app architecture
ui layer
state holders and ui state
Do you think this is the best way of doing what I want?
i am not very sure that i got exactly what your app do, but it seems like you want to re-order the elements of recycle view depending on the ui event (click) or data change (deleting or adding new element), now you have two choices:
if the order is very importnat to you that much you want to keep it even if the app has been destroyed
then you have to add a field in the room entity represent the ordering (let us call it order) and whenever the user click on the recycle view you have to update the rooms field "order" which is "flow" or "liveData" or any observable type, that will tell the view model that there is a changing in the data, now the view model have to re-order the new data by the field "order" and pass it to the recycle view to show it.
if your app do not have to save the order changes after the app been destroyed
then you can simply do that:
create list which is called "orderedList" you will put the list items in it by the right order, and another list called "unorderlist" which have getAllLists
for the first case where the ordering is being changed by user click, you
can declare a function in viewModel then use it in the ui
controller (your activity or fragment), so whenever the list item is
clicked this function just re-order the orderedList elements ( which
is observable, so the changes reflect on the ui ) just by change the
clicked item position to the front of the list.
for the second case where the ordering changes by data changes like
add or delet a list item in the database, then you have to compare
the legnth of orderlist and unorderlist legnth, if unorderList is
longer then it is an add situation else it is a delete situation, in
adding case just add the last item of unorderList to the orderList,
else you have to check the deleted item and delete it from
orderList.
This question is about Couchbase lite (no Sync Gateway).
I'm new to Couchbase, I managed to use the demo app, but I don't understand it completely.
It contains this code which (as far as I understand, since I'm not native English speaker) retrieve views to populate a listview with the indexes:
// This code can be found in ListsActivity.java
// in the setupViewAndQuery() method
com.couchbase.lite.View listsView = mDatabase.getView("list/listsByName");
if (listsView.getMap() == null) {
listsView.setMap(new Mapper() {
#Override
public void map(Map<String, Object> document, Emitter emitter) {
String type = (String) document.get("type");
if ("task-list".equals(type)) {
emitter.emit(document.get("name"), null);
}
}
}, "1.0");
}
listsLiveQuery = listsView.createQuery().toLiveQuery();
Could anyone give me a hand with what each part is doing?
In which step is the listview populated
Can I change "list/listsByName" in the code (line 3)? What would happen?
Can I emit more than one element?
The code is a little bit convoluted. Let's answer the easy parts first.
Can I change "list/listsByName" in the code (line 3)?
Yes. That's just the name of the Couchbase View. You choose the View name. Unfortunately the terms used in Couchbase and Android overlap some. A Couchbase View is a kind of static index of your database.
Can I emit more than one element?
Yes. You can emit most anything you want. Take a look at the documentation here
Now, tracing how the Android ListView gets updated:
In ListsActivity.java notice in the onCreate method a ListAdapter instance gets added to the ListView. This ListAdapter is a private inner class that extends LiveQueryAdapter.
LiveQueryAdapter is in the utils subpackage. If you look at its constructor, you'll see it adds a change listener to the query passed in. When triggered, this change listener sets an enumerator equal to the rows passed back by the live query, then calls notifyDataSetChanged to tell the list to refresh itself. That, in turn, causes getView in ListAdapter to get called. That's where the data is pulled from the database and used to populate a list entry.
I want to populate RecyclerView using database. As currently there is no inbuilt adapter for populating RecyclerView using database, I have used CursorRecyclerAdapter by Shywim. I have created a sample App to test it and it worked fine. The feature I didn't liked is having an _id column in the resultset and calling swapCursor() on each database operation, mostly insert and delete. This goes same with ListView when using SimpleCursorAdapter. My query is what if I use ArrayList as the dataset instead of directly using the Cursor.
Benefits of doing this(my assumption) :
No more a need of _id column in the resultset.
Can fetch the data from database, put it into ArrayList and close the cursor.
No need of calling swapCursor() on each database operation as I can add/remove specify elements from the ArrayList and call notifyDataSetChanged()
I don't know the exact logic behind swapCursor() and notifyDataSetChanged(). So, can't decide which one is light-weight and efficient.
If someone has experienced this or done this before, please clear my doubts. Any corrections and suggestions are most welcome.
Using array list and custom adapter is better way for this as per my understanding.
See some scenarios below :
1) Cursor will close after each transaction so database will work smoothly.
2) As you can close cursor on operation done so it will never generate cursor not closed exception.
3) You can modify view of each row easily and manage custom adapter as per your choice.
There are many other reasons, but in short custom adapter is better then cursor adapter as per my understanding.
I am new to Android and am trying to get my header round the SimpleCursorAdapter and CursorLoader classes. From my understanding, all of the examples that I have seen use these two classes to load data into a ListView in a background thread (to not block the UI).
I am OK with this and have used this general approach with my own list of items, however I now want to be able to click on an item in the list and get the full information for the item. Is it usual practice to use SimpleCursorAdapter and CursorLoader to retrieve the details for a single item? or are they just meant for lists?.
Thanks.
They are not meant for lists only. You can - and should - use them in detail views (activities) as well.
I've sketched a possible way to do so on my blog:
http://www.grokkingandroid.com/using-loaders-in-android/
Think of Adapters as a layer of abstraction between your data (Cursor) and whatever you attach that Adapter to (ListView for example). This way, you have a common interface between your data (Cursor, ArrayList, whatever) and the View you display that data on (ListView, TableView, etc.), this is helpful because if you later find that you want to access your data through an ArrayList rather than a Cursor, then you simply swap out the adapter with a different one and you're ready.
Now considering your question, Adapters give an abstract access to information, therefore you can "ask" it for what information is stored and where. You could attach an OnItemClickListener to your ListView and then access your data from there.
I have a ListFragment backed by an ArrayAdapter that gets populated by a Loader. When the user clicks on one of the items, I want to pass a reference to the selected item, as well as the rest of the list items to another fragment. My question is how should I get all of the items from the adapter? Here are the possibilities that I see:
1. Keep a reference to the backing List
Create the adapter like so:
List<DomainObject> items = new ArrayList<DomainObject>();
listAdapter = new ArrayAdapter<DomainObject>(getActivity(), R.layout.mine, items);
and then simply pass items or a copy of it to the next activity.
The downside I see of this is that I'm relying on the undocumented fact that the same list that I pass to the constructor contains the items later on.
2. Iterate through the adapter
When an item is clicked, iterate through the adapter and build up the list. This seems like an unnecessary amount of work. The items are contained in a List in the adapter and I'm manually copying each item to a new list.
3. Keep a separate list of items when adding to adapter
Before adding an item to the adapter, add it to a separate list that I maintain in the fragment. This is also wasteful as the list of items is copied in the ArrayAdapter and the fragment.
I'm a little late to the game, but I've run up against a similar issue.
One way to deal with #1 would be to maintain the reference to the list within a subclass of ArrayAdapter, so that your reuse is controlled by the adapter object.
Something like:
public class DomainAdapter extends ArrayAdapter<DomainObject> {
private final List<DomainObject> items;
public DomainAdapter(Context context, List<DomainObject> items) {
super(context, R.layout.mine, items);
this.items = items;
}
public List<DomainObject> getItems() {
return items;
}
}
The solution that I've gone with in the meantime is just to not use ArrayAdapter. In cases where you're fighting against this API, it seems like it's better just to use the less fully-featured (and complex) BaseAdapter. You can read more about the decision to go with BaseAdapter instead of ArrayAdapter in this article: Android Adapter Good Practices.
A quick test says that method 1 works. It seems the quickest and cleanest, but since it is undocumented you may want to test it across the intended platforms and whenever they update in case the underlying structure of ArrayAdapter changes.
I am using compile SDK version 22 and min SDK Version 10.
The best method is to "keep a reference to the List" BUT not passing "items" variable/parameter to the Constructor:
List<DomainObject> items = new ArrayList<DomainObject>();
listAdapter = new ArrayAdapter<DomainObject>(getActivity(), R.layout.mine);
In this way you only instantiate the ArrayList as an empty array and you will have to manage YOUR list by yourself.
I think first method is best way to do this.
I dont think, Data would be original for the Another Activity. because, You would pass items through bundle, so the object is written on bundle first and then in next Activity we read from bundle.
However, if you are using some other way to pass the list, use list.clone() to create new Object, instead of passing original one.