SectionIndexer - Using with ArrayAdapter and CustomObject?

Question

I am following a great coding example over here: This SO question. It is regarding implementing a SectionIndexer interface to an array adapter.

However, how would you do the same thing if your ArrayAdapter is passing an ArrayList< MyObject > not an ArrayList< String >?

For example, this is where my code is different then his code. He has:

class AlphabeticalAdapter extends ArrayAdapter<String> implements SectionIndexer {
private HashMap<String, Integer> alphaIndexer;
private String[] sections;

public AlphabeticalAdapter(Context c, int resource, List<String> data) {

    alphaIndexer = new HashMap<String, Integer>();
    for (int i = 0; i < data.size(); i++) {
        String s = data.get(i).substring(0, 1).toUpperCase();
        alphaIndexer.put(s, i);
    }

    // other stuff

 }

I am having problems adapting that for loop to my situation. I can't measure the size like he does. Where he has the above, my adapter begins with.

 public class CustomAdapter extends ArrayAdapter<Items> implements
    SectionIndexer {

     public ItemAdapter(Context context, Items[] objects) {

Where he is passing one ArrayList, I have to pass in three, but to make that happen, had to wrap in a custom object class. One of the ArrayLists that I want to sort is one of three fields in the class called "name". It is a string obviously.

I want to scroll through that alphabetically with SectionIndex based on that name field. How do I change the example code from the other question to work in this scenario?

Where he has "data.size()", I need something like "name.size()" - I think?

Answer 1

Where he is passing one ArrayList, I have to pass in three, but to make that happen, had to wrap in a custom object class. One of the ArrayLists that I want to sort is one of three fields in the class called "name".

You don't have three ArrayLists, you have an ArrayList of custom objects that were built from three ArrayLists(so the size is the size of the List that you pass to the adapter). From this point of view the only change in your code is to use the name from that custom object Items to build the sections:

for (int i = 0; i < data.size(); i++) {
    String s = data.get(i).name.substring(0, 1).toUpperCase();
    if (!alphaIndexer.containsKey(s)) {
        alphaIndexer.put(s, i);
    }
}
// ...

There aren't other changes. Also you may need to sort the List of Items that you pass to the adapter using:

Collections.sort(mData);

where your Items class must implement the Comparable<Items> interface:

    class Items implements Comparable<Items> {
        String name;
        // ... rest of the code

        @Override
        public int compareTo(Items another) {   
            // I assume that you want to sort the data after the name field of the Items class
            return name.compareToIgnoreCase(another.name);
        }

    }