I have a ListView
with a hypothetical SquirrelAdapter
. Something like this:
public class SquirrelAdapter extends ArrayAdapter<Squirrel> {
private LayoutInflater layoutInflater;
private Context context;
private int resource;
public SquirrelAdapter (Context context, int resource, List<Squirrel> squirrels) {
super(context, resource, squirrels);
layoutInflater = LayoutInflater.from(context);
this.context = context;
this.resource = resource;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
Squirrel squirrel = getItem( position );
convertView = layoutInflater.inflate(resource, null);
TextView squirrelNicknameTextView = (TextView) convertView.findViewById(R.id.squirrelNickname);
squirrelNicknameTextView.setText( squirrel.getCuteNickname() );
return convertView;
}
}
So in an activity
I can do this:
Squirrel[] squirrels = // Lot of Squirrels
SquirrelAdapter squirrelAdapter = new SquirrelAdapter(
getApplicationContext(),
R.layout.squirrel_layout,
Arrays.asList( squirrels )
);
squirrelListView.setAdapter( squirrelAdapter );
And so I can append an onItemClickListener
:
squirrelListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
// Bad people cast a squirrel :|
Squirrel squirrel = (Squirrel) parent.getItemAtPosition(position);
Log.i("WWF", "Tapped squirrel " + squirrel.getCuteNickname());
}
});
It works really well. But now the really boring question:
How can I use Java's parameterized type in AdapterView<T extends Adapter>.setOnItemClickListener
? I'm thinking something like below, but it gives errors:
squirrelListView.setOnItemClickListener(new AdapterView<SquirrelAdapter>.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<SquirrelAdapter> parent, View view, int position, long id) {
// Squirrels approved!
Squirrel squirrel = parent.getItemAtPosition(position);
Log.i("WWF", "Tapped squirrel " + squirrel.getCuteNickname());
}
});
Why can't I have syntax such as "
AdapterView<ArrayAdapter<T>>.OnItemClickListener
"?Why doesn't something like this exist:
<T> getItemPosition(int position)
? Can it be implemented?
Thanks helping my squirrels not to be casted.
(More seriously I want to learn more about this Java feature...)
As you might have seen if you try new AdapterView<SquirrelAdapter>.OnItemClickListener()
compiler would say,
The member type AdapterView<SquirrelAdapter>.OnItemClickListener cannot be qualified with a parameterized type, since it is static.
What you are doing inside listView.setOnItemClickListener
is to create an Anonymous
class, for an interface OnItemClickListener
inside abstract class AdapterView
. Now, to get reference of interface
inside an abstract
class, you need to access only statically, such as AdapterView.OnItemClickListener
, and hence the compiler error as above.
Even if you try to create a concrete class that implements
OnItemClickListener
you have to access statically only, such as class MyImpl implements MyAbstract.MyInterface
If you have noticed signature of AdapterView
class
abstract class AdapterView<T extends Adapter>
that indicates, AdapterView
can have Adapter
or any subtype of it as its parameter. But to get hold of elements(data) Adapter
is connected to, AdapterView
uses
Object getItem(int position);
As you could see inside:
public Object getItemAtPosition(int position) {
T adapter = getAdapter();
return (adapter == null || position < 0) ? null : adapter.getItem(position);
}
Casting of your Squirrel
inside onItemClick
is needed. See if it helps!