I know a list view needs an adapter, but WHY what is the purpose of it, and can it show lists without an adapter ?
An adapter manages the data model and adapts it to the individual rows in the list view.
Filtering and sorting of the data is handled by the adapter.
The notifyDataSetChanged() method on the adapter is called if the data has changed or if new data is available.
The notifyDataSetInvalidated() method is called if the data is not available anymore.
Also see What's the role of adapters in Android?
From the docs:
An Adapter object acts as a bridge between an AdapterView and the
underlying data for that view. The Adapter provides access to the data
items. The Adapter is also responsible for making a View for each item
in the data set.
The ListView needs to know which items to show, and needs to get Views for these items. The Android team chose to implement this using Adapters.
Note that for showing simple lists of Strings, there is the ArrayAdapter class.
Related
I have a situation that I must get some data from the database with a button click in Recyclerview item and fill the Recyclerview adapter again with new data.
Should I put the database fetch code in button onClickListener in the adapter or it is better to do it in another way? For example with help of Callback in activity.
It is a definitely bad scenario, because database belongs to model and RecyclerView - to View layers. All presentation logic will be in adapter (along with execution in background). It will lead to difficult to maintain application.
I trying to refactor one of my activity class to implement mvp(using mvp mosby library) . I have a RecyclerView and in this view there is some items that some changes apply to them during the run time. for example I do some I/O operation and change one row.
I think it's better to keep my items in presenter class; what is the best practice for this? keep this in 1)presenter or 2)activity or 3)only keep view related item in adapter and all other item in presenter.
the activity now keep items directly and change item row in activity and then notify adapter. isn't better to move all this line in adapter and notify adapter in the adapter class? for example i want change icon of some row.where and which class is responsible for that? adapter? activity? now I want to implement it like this in adapter:
changeItemIcon(int position, int iconRes){
mImages.get(position).setICon(iconRes);
notifyItemChanged(position);
}
I invoke this method on activity and invoke activity method from presenter.
is it good? what is the best practice to do this?
UPDATE
also I find this question ( Best way to update data with a RecyclerView adapter ) that using adapter method for changing items. but what about modify? Need I keep reference to items in my activity?
for example i want change icon of some row.where and which class is responsible for that? adapter? activity?
I know it sounds a little bit strange, but changing an element is always the responsibility of your "business logic", even just for "icons".
The workflow should be as follows (unidirectional data flow):
View appeares, tells presenter to load a list of items
Presenter loads items form "business logic" and registers himself as an
observer / listener / callback (whatever you want to call it)
Presenter receives result and tells the view to display the list of
items (through RecyclerView and corresponding adapter).
so far is what you have implemented I guess, now it comes to the point where you want to change an item.
User clicks on an item in your RecyclerView which then should trigger to change the icon of this item. Therefore View should call: presenter.changeItem()
Presenter is just the man in the middle in this case and will invoke the "business logic layer" to tell that the item should be changed to new state (icon has changed).
"Business logic layer" will change the models state (change the items icon) and then will notify its observer / listeners that the model has been changed.
Since Presenter is still observing / listening to the business logic layer (see point 2.) the Presenter will be notified (see point 6.) with a new (updated) list of items containing the updated item which icon has been changed.
Similar to point 3. Presenter will tell the view to display the new (updated) list of items (through RecyclerView and corresponding adapter).
Do you see the unidirectional data flow? That is very important. Immutability FTW.
MVP has two different variants: Passive View and Supervising Controller. Depending on your taste, you can stick to one or mix both of them in your app.
If you choose Passive View, you need to hide Model from View and let Presenter format data then set to the View. In this case, you need to keep Model reference in Presenter. View should only hold view-data (adapter) for its displaying purpose.
If you stick to Supervising Controller, you can allow View to directly bind data from Model and ask Model to perform some simple logic. Presenter should only care complex logic, i.e some operations which need to involve Services. In this case, you can give Model (your items) to View (activity) and let it interact with Model in some simple manner.
PS: Please also check out our new MVP framework: Robo MVP at http://robo-creative.github.io/mvp.
I've never used mosby, but I've just read their docs (good reading btw) and here's my understanding:
A recycler view usually consists of the view (android term) and an adapter. Both are connected inside a fragment or activity. In terms of MVP/mosby this is all view layer. The presenter should only retrieve and pass the to-be-shown data from your service (model layer in mosby, "service layer" or "business logic" in other concepts), which in turn gets it from a DAO or repository (model layer).
The docs say that the presenter only handles the view state, not the actual contents. Your state is "showing list".
I'm using the navigation drawer example in Android. What's the easiest way to change the string items in the adapter dynamically? Do I just create a new adapter and set it with my new values?
The problem is I'm altering the string items based on user state logged in and logged out. How do I access it from a non static context and just say update list adapter? It doesn't seem to be re-drawing itself and running my adapter code which is dynamic based on user state, so I guess it runs/inits once and I have to create and load a new adapter if I want to change it later?
Thanks.
You haven't given us much to go on (a little code would be nice), but you can update the data in the ListView by calling notifyDatasetChanged() on the Adapter. If you are not using a custom Adapter e.g. an ArrayAdapter then you can just create a new Adapter instance with different String values and set it to the ListView.
I have a ListView.
I'm using anArrayAdapter and I'd like to:
when the user clicks any item on the list, its LinearLayout (is just a content for x information) fades out and is substituted by other LinearLayout (with y information) which fades in.
However, I do not know how to apply this on my ArrayAdapter. I've searched for a while but I'm not understanding how can I access a single item from the Adapter and make it's children fade out or fade in.
Any help would be very appreciated. Thank you very much for your time.
In general - adapters do not hold items the role of adapter is to get data model, and to produce item views when i.e. list view needs them.
The main concept of replacing item is to replace data inside the adapter and call notifyDataSetChanged(); - thats all.
I don't like ArrayAdapter as it's aimed for very simple scenarios. Usually I just create my own Adapter class extending BaseAdapter (just 4 methods to implement).
The transitions of items on ListView are described here: Adding animation to a List View in Android
I currently use a bunch of subclassed CursorAdapters with custom layouts throughout my app, populating them with a Cursor returned by an SQLite query, then allowing them to populate my ListView, after setting them with
setListAdapter(new SearchAdapter(this, searchCursor));
Is there anyway I can get the same behavior but instead of passing in a Cursor pass in an
ArrayList<String[]>
Would there be a different class to subclass? (Obviously) Or, should I convert the ArrayList to a Cursor somehow? Or, is there a different method I am missing?
Thanks!
you can do it with an array Adapter (also you can subclass Base adapter) and implement your own way of displaying objects in a list. there are plenty of tutorials on google on how to do that.
Just search ArrayAdapter, Base adapter. :D
Hope this helps,
Take care.