Develop Reference

Why do we use single adapter per class in android?

I have just started learning android using Big Nerd Ranch Guide. In a project, we were to implement a listView and get the data from an array using an ArrayAdapter, as the crime objects were stored in some list.
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
getActivity().setTitle(R.string.crimes_title);
mCrimes = CrimeLab.get(getActivity()).getCrimes();
ArrayAdapter<Crime> adapter =
new ArrayAdapter<Crime>(getActivity(),
android.R.layout.simple_list_item_1,
mCrimes);
setListAdapter(adapter);
}
After that, we were to create custom list to display the title as well as the checkbox and date so we created a custom layout. Now, we used a different adapter for that purpose.
private class CrimeAdapter extends ArrayAdapter<Crime> {
public CrimeAdapter(ArrayList<Crime> crimes) {
super(getActivity(), 0, crimes);
}
My question is why cant we use the same adapter that we used earlier?I mean we can just give it new values or create a new object.I searched the internet and found that we can create multiple adapters with some restrictions. why we extend it to ArrayAdapter? cant we just do it like we did previously by creating the adapter?
Please explain in detail, as I have just started.
Thanks.

Let us talk about the list view adapter implementation in android first of all in your first example you used the default implementation of listview adapter in android which provide you with list view of text
but most of the time this is not enough for your user interface you want to add an image a checkbox like in your second example so android OS gives you the ability to make your own custom cell (each row in list) that's why you would find yourself in a need to extend array adapter
in your first example you used
android.R.layout.simple_list_item_1
which is a layout containing only textview
and you provide a data source mCrimes
so when you extend array adapter you do the same you provide your own layout which represent the cell and a data source which will populate your list
hope that clarify it for you and welcome aboard :)

How to create custom dynamic list in android?

I want to create a custom list in which items are added or removed dynamically (say when a button is tapped). The problem is I have very little knowledge of lists in android. I have gone through various tutorials on creating a custom list in android but none of them shows how to dynamically add contents to it
What I know so far:
1) I have to create a model class to store data.
2) I have to create an adapter class.
3) Pass the objects of the model class as an arraylist to the adapter.
3) Bind listview to the adapter
What's confusing me:
1) I know I have to create an apapter class, but what's really confusing me is what kind of adapter ? i.e. ArrayAdapter, BaseAdapter ??
2) What and How will I feed adapter? I will be fetching data from the Sql lite database and I want the results to be displayed in my custom made list.
3) How will I update my list when a new record is added to the database ? I know how to populate listview from a static array but its of no use in my project.
I need little guidance where should I start from ?

1) You can use ArrayAdapter.
2) After you create your own arraylist, you can pass it for first time, listview.setAdapter(...
3) After you refresh your data you can call this method, ((ArrayAdapter)listView.getAdapter).notifyDataSetChanged(). This will ensure your listview refresh.
The below link is a good example:
https://github.com/thecodepath/android_guides/wiki/Using-an-ArrayAdapter-with-ListView

StableArrayAdapter vs ArrayAdapter

I am looking at this ListView Tutorial:
ListView Tutorial
and I was wondering how much better is to create my own ArrayAdapter, rather than just using and ArrayAdapter.
In the Tutorial it defines a "StableArrayAdapter", what exactly does this means? If I use a regular ArrayAdapter, could it be dangerous for some reason?

The two previous answers are absolutely right, but just to address more directly your question and in case someone else has the same doubt than you; a regular ArrayAdapter is not dangerous at all, the only "problem" is that it might not fulfill your needs, in which case you will have to create your own adapter, as the author of the tutorial did by creating what he called StableArrayAdapter in the end of the ListViewExampleActivity class.
Don't get lost by the name, which I guess comes from the fact that the overwritten method "hasStableIds" always returns true, it doesn't mean that the regular ArrayAdapter creates problems.

ArrayAdapter: It is merely a way to provide data to a ListView. It is also a BaseAdapter that is backed by an array of objects.
CustomAdapter: If if your ListView is a normal and simple ListView (wherein you are having one TextView per item in the list), then the use of ArrayAdapter would be apt.
But it is recommended you to create your own CustomAdapter which extends an ArrayAdapter that you can use for providing data to your ListView. This way you can easily extend your ListView to include more that one TextView or even ImageView (to show images).
CursorAdapter: Cursor Adapter is used when you have Data in a Cursor (typically when you are retrieving data from a database. The Cursor must include a column named "_id" or this class will not work.

If you are using a simple ListView, like merely a TextView per item, then just use the standard ArrayAdapter, on the other hand, if you want a custom item in the list, as in a combinations of views within each item in the ListView, then extend the ArrayAdapter and implement it to your needs.

StableArrayAdapter is merely an extended version of ArrayAdapter, but in StableArrayAdapter they have overridden the method hasStableIds() of BaseAdapter to return true.
You can check this in the following links:
StableArrayAdapter -
Override hasStableIds to return true
ArrayAdapter -
Has not Override hasStableIds but extended BaseAdapter
BaseAdapter -
Has hasStableIds but returning false
Now Question is What is the use of StableIds
This Indicates whether the item ids are stable across changes to the underlying data. If True then same id always refers to the same object. for more info

declare Array adapter in the non-activity class to use in the fragment

So here is my problem. I'm using a dialog fragment to display some info. In that fragment, i have a spinner view that is filled up by the Array list. Normally I create that adapter in my fragment like this:
ArrayAdapter<String> teamsAdapter = new ArrayAdapter<String>(getActivity(),
android.R.layout.simple_spinner_item, Variables.teamNames);
teamsAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
Variables.spinner.setAdapter(teamsAdapter);
Variables is my user-defined class where I keep all variables.
Now here is my question. I have around 10 DialogFragments and almost all of them have spinner. I would like to define that Adapter in my Variables class and whenever i need it, i would just call it from my variables class. Unfortunately to do that, i need getActivity() in my adapter constructor. I cannot go around it.
BTW, is it a good idea or I should use interface?
It would be awesome if somebody could actually tell me why would I use java interface in android?

Your fragment would still need to call some Variables method to retrieve the spinner and to add it to your layout, right? So when you do that call, you can pass the Activity as Context, something like this:
ArrayAdapter<String> teamsAdapter = Variables.getAdapterForTeams(getActivity());
The question about the Interface isn't an Android but a Java question. If it makes sense to use an Interface in Java it will make sense to use it in Android. There's plenty of literature and online resources about Java that will explain the why and when Interfaces should be used. I'm sure if you search online you'll find plenty of resources about it.

Display GridView inside ExpandableListView for unknown groupCount in Android

I'm having a class (ExpandableListDataClass) which extends BaseExpandableListAdapter
I am calling to ExpandableListDataClass from an Activity like below;
ExpandableListDataClass expandableListDataClass = new ExpandableListDataClass(this, categories);
categoryExpandableListView.setAdapter(expandableListDataClass);
categories is a String array. That means groupCount of the ExpandableListDataClass is depend on the categories.
The worst thing is, I am loading a GridView for expanding of a group item in ExpandableListView. Those GridView have different data to show according to the category.
If I use following code inside getChildView(), it is perfectly working
if(getGroup(groupPosition).toString().equals("ebooks")){
expandableListInsideGridView.setAdapter(eBooksImageAdapterForExpandableList);
}else if(getGroup(groupPosition).toString().equals("ebrochures")){
expandableListInsideGridView.setAdapter(eBrochuresImageAdapterForExpandableList);
}
But what I want to remove from that is eBooksImageAdapterForExpandableList and eBrochuresImageAdapterForExpandableList. Because now what I am doing is creating ArrayList according to the existing categories.
But when I don't know how many categories/groupCount there are, I can't do that.
Please give me a solution

Finally I was able to find a solution :-)
I will explain it in backwards.
In the getChildView() I have to give following line of code
expandableListInsideGridView.setAdapter(new ImageAdapterForExpandableList(expandableListDataClassContext, eItemThumbCachePathArrayListContainer.get(groupPosition), eItemNamesArrayListContainer.get(groupPosition), eItemUrlArrayListContainer.get(groupPosition)));
getChildView() is in the ExpandableListDataClass which extends the BaseExpandableListAdapter.
What I had to do is declare an ArrayList which contains some other ArraLists of same type. If I explain it more with my code eItemThumbCachePathArrayListContainer is an ArrayList which contains ArrayLists of type String that I want to pass. That is the simple logic I have used and it works for me.