使用Map接口而不是List接口的实现在BaseAdapter中存储数据

Question

I want to use one of the implementations of the Map interface instead of implementing the ArrayList to store data in BaseAdapter. I'm looking for the best way to get values from Map by index. Creating lists from map when i have index seem to be highly not efficient.

@Override
public Object getItem(int position) {
// TODO Auto-generated method stub
List<Map.Entry<String, String>> 
list = new LinkedList<Map.Entry<String,String>>(this.countries.entrySet());
return list.get(position);
}

Any suggestion how to do it in right way?

Thanks in advanace.

Answer 1

For performance, you need to keep ArrayList with values of your Map in your adapter separately :

// Map<String, String> countries;
ArrayList<String> countryList = new ArrayList<String>(countries.values());

You will also need to update the list every time your map changes and you are about to call notifyDataSetChanged()

This way, you get optimal O(1) performance (as it should be) for your getItem() :

@Override
public Object getItem(int position) {
    return position < countryList.size() ? countryList(position) : null;
}

and don't forget to return correct value in getCount() :

@Override
public Object getCount() {
    return countryList.size();
}

Note, there will be no guarantee on how values of your list (coming from the map) will be ordered, so you may want to sort them as well.