Question

I’m having issues with an Android AutoComplete dropdown menu. I am trying to pass a custom object into a new ArrayAdapter, which is then used for the data in the dropdown menu. However, I’m getting the following error for this line of code:

adapter = new ArrayAdapter<String>(_context, R.layout.list_item, list_items);

The constructor ArrayAdapter<String>(Context, int, DropdownItemData[]) is undefined

I’ve tried running this as well, which outputs a type mismatch error:

adapter = new ArrayAdapter<DropdownItemData>(_context, R.layout.list_item, list_items);

Type mismatch: cannot convert from ArrayAdapter<DropdownItemData> to ArrayAdapter<String>

However, the following does work just fine:

String[] test_list = new String[] {"some", "test", "data"};
adapter = new ArrayAdapter<String>(_context, R.layout.list_item, test_list);

My DropdownItemData class overrides the Object toString() method, as is recommended in the ArrayList documentation here:

http://developer.android.com/reference/android/widget/ArrayAdapter.html

Does anyone know what the issue is/what I’m missing? According to the docs, the constructor I’m trying to use for ArrayList should just be taking a generic list–so I don’t understand what the error is complaining about.

Answer 1

The class name is ArrayAdapter<T>. And the constructor signature is ArrayAdapter(Context context, int textViewResourceId, T[] objects).

So if you declare your variable as an ArrayAdapter<String>, you must pass an array of String as last argument of the constructor.

To be able to pass it an array of DropdownItemData, your adapter must be of type ArrayAdapter<DropdownItemData>.

You can put a lion in a Cage<Lion>, and a bird in a Cage<Bird>. But you may not use a Cage<Lion> with birds, nor a Cage<Bird> with lions.

You should read the generics tutorial.