Can anyone tell me what exactly does an array adapter do? I've tried searching the net but all I get is code examples. Please explain me what it does, I've visited the android developers as well.
An ArrayAdapter can be used as a data source for a number of different Android Views, such as a ListView or a Spinner.
Basically, you pass some kind of array or list to the constructor of an ArrayAdapter. Then, the adapter can be hooked up to a ListView by calling setAdapter(). You can also use the add and remove methods of the adapter to modify the underlying list itself.
You can also use an ArrayAdapter to customize the appearance of items in a ListView for example (or other Views) by using the constructor and passing in the resource of a layout to use, or by overriding the getView() method and building it yourself.
Typically, an adapter is some kind of translator. It's the "man in the middle" who know how to dialog with both sides and convert what is said.
An arrayAdapter is a class which get datas from an array and format it for a listview or spinner to understand it. When a listview need the data 4, for example, it will ask the adapter who will return him the 4 element of the array.
Ok, the listview could directly use the array.But with the adapter you're allowed to use any kind of data source. An ArrayAdapter(subclass of adapter) uses an Array, but another adapter could use a database or a file or anything else.That way the listview is able to get datas directly from any source without knowing how to access it.That is the adapter's role.
Related
I have a ListView where the view for each item is a string (the name of the item). But I have to associate a lot of other data with that item: price, size, weight, tax, etc. So, I'm of creating a new Java class called Item, and then an object for each item in the list.
I don't know which is the bext way to implement this. There's two obvious choices:
1) I can simply create the data structure outside of any Android Views, and then write a method called UpdateList() which takes the name of each item in this data structure and puts it in the ListView. The problem with this is that some of the data is duplicated twice (the original data structure, and the adapter for the ListView) and when you duplicate data, bug potential arises.
2) Or, I can somehow associate the data structure directly with the adapter for the ListView and have it figure out how to display the name for each ListView entry that is displayed. The advantage here is that you only have a single data structure. But I don't know if this is possible in Android, or very complex.
Which is the preferred way to do this with Android apps?
You would be better with the ListView and the Adapter option, You would need to create a custom ArrayAdapter to populate a ListView from this objects the way you want.
The advantage of this technic is that you gain a Views recycle mechanism that will recycle the Views inside you ListView in order to spend less memory.
In Short you would have to:
1. Create an object that represents your data for a single row.
2. Create an ArrayList of those objects.
3. Create a layout that contains a ListView or add a ListView to you main layout using code.
4. Create a layout of a single row.
5. Create a ViewHolder that will represent the visual aspect of you data row from the stand point of Views.
6. Create a custom ArrayAdapter that will populate the rows according to you needs.
7. Finally assign this ArrayAdapter to your ListView in onCreate.
You can get an Idea of how to implement this by reading this blog post I wrote:
Create a Custom ArrayAdapter
Just use the adapter. It's much cleaner. Then you can retrieve the info you need when you display the list item with getView(). See this example.
I know there are several adapters to manipulate listviews like ArrayAdapter, BaseAdapter, CursorAdapter and so on, but I don't how to choose the best solution for my needs... I mean, when I'm choosing the adapter, which are the criterias that I should check before select the adapter to use?
Every kind of help will be appreciated!
The major concern in adapter selection is how you get your data to populate the list.
If the data is coming from a database/cursor, you should use one of the cursor adapters. You could use an array adapter, but that would just be unnecessary computational cycles to transfer the cursor data to the array before setting the adapter.
If your data is in an array then your obvious choice is one of the array adapter types.
If your data is coming from different sources, you'll need to create your own adapter or modify one of the existing ones.
After the incoming data format consideration might come thought on list modification and which adapter would work best with whatever needs you have to modify the list (and/or the data backing it).
How can I organize a spinner alphabetically that has its fields in a listView without manually changing the field data?
I'm not sure I totally understand the question, but here goes.
You can populate the spinner in a similar way that you populate the ListView. That is by using an Adapter. When you create the adapter that you're using for the ListView, make one that you'll use for the spinner.
The type of adapter you use will be based on where the information you're using is coming from.
Does this help?
Hello
I am trying to build a listview based on content from the web.
I have had a look at :
http://androidboss.com/load-listview-in-background-asynctask/
example but it uses a predefined array of months. How can I substitute the known
array of months for an unknown undetermined number of items from the internet?
I want to load a listview with some data from the internet, the user
scrolls the list and it retrieves the next row(s) from the internet etc etc
rather than using a array of predetermined length.
Thanks Ian
You can use my EndlessAdapter for that. The project has a demo/ subproject demonstrating its use.
It sounds like you need to extend an adapter such as ArrayAdapter. Extending an ArrayAdapter so that you can dynamically generate the rows or alter the number of rows, and also notify the Adapter that the underlying data has changed, is a very common exercise in Android.
You'll find quite a few tutorials on this but, very basically, if you implement your own adapter by extending ArrayAdapter you can override getView() to programmatically generate each view, and you can override getCount() to provide the number of rows. You can use notifyDataSetChanged() to trigger a refresh of the list on the screen if some data has changed and you need to refresh.
I am going to make a grid of images and I am trying to figure out whether to use an array adaptor or a baseadaptor. While the GridView example, stores the data in an array, it uses a BaseAdapter rather than a ArrayAdaptor. I am curious why this is. One thing I noticed about an ArrayAdapter, is that its constructor takes a textViewResourceId for some unknown reason - although the documentation say the getView can be used to make it work with other kinds of views as well. So, if I want a fixed grid of images for a menu, which class would you recommend choosing?
You typically choose your adapter class based on what the model data is. If you have an ArrayList of objects, use ArrayAdapter. If you have a Cursor from a database query, use a CursorAdapter. BaseAdapter can be used for anything, but it requires more coding, since it has no innate knowledge of how to iterate over the data.