How to sort HashMap as added in Android with ArrayAdapter

Question

I have a HashMap<String,String> and there is a static method which returns this map to an Activity.

Method looks like this:

public static HashMap<String, String> getAll() {    
    HashMap<String, String> map = new HashMap<String,String>();

    map.put("ab", "value1");
    map.put("bc", "value2");
    map.put("de", "value3");

    return map;
}

I want to use that map with a spinner. So activity looks like this:

List list = new ArrayList<String>();
HashMap<String, String> map = Constants.getAll();

for (String key : map.keySet()) {
    list.add(Constants.getAll().get(key).toString());
}

ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, list);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);

spinTest = (Spinner)findViewById(R.id.spinTest);

spinTest.setOnItemSelectedListener(new OnItemSelectedListener() {
    public void onItemSelected(AdapterView<?> arg0, View arg1, int arg2, long arg3) {
        urlDebug.setText(list.get(arg2).toString());
    }

    public void onNothingSelected(AdapterView<?> arg0) {

    }
});

spinTest.setAdapter(adapter);

When I tried to run my application, no problem at all. But when I clicked on spinner, items not ordered as I added on getAll() method. I mean, order has to be ab - bc -de but it's ordered randomly.

What's not true?

Answer 1

in hashmap, insertion order is not maintained, so item inserted last may accessed first. If you want to maintain order of insertion, use linkedhashmap instead.

Answer 2

Update : Answer by jitendra sharma is the best : A treemap costs a lot more than a linkedhashmap and adds nothing to your project if you only need to keep original insertion order.

Hashmap cannot get sorted. That's part of their efficiency.

If you need sorting, then use a TreeMap.

Good luck.

Answer 3

You should either call adapter.notifyDataSetChanged() or spinTest.setAdapter(adapter) after you sorted your list.

spinTest.setOnItemSelectedListener(new OnItemSelectedListener() {
    public void onItemSelected(AdapterView<?> arg0, View arg1, int arg2, long arg3) {
        urlDebug.setText(list.get(arg2).toString());
    }

    public void onNothingSelected(AdapterView<?> arg0) {

    }
});

spinTest.setAdapter(adapter);
// TODO: Sort the list
// Some code here
adapter.notifyDataSetChanged();