Question

I have google’d it, and tried some examples, but I always get stuck.

This is the error message, when I try to use the Collections.sort:

The generic method sort(List<T>) of type Collections is not applicable for the arguments (ArrayList<HashMap<String,String>>). The inferred type HashMap<String,String> is not a valid substitute for the bounded parameter <T extends Comparable<? super T>>.

My code is similar to this one.

ArrayList<HashMap<String, String>> mylist = new ArrayList<HashMap<String, String>>();

//Get the data (see above)
JSONObject json = JSONfunctions.getJSONfromURL("http://xxxxxxxxxxxxxxxxxxxxxx");

try {
    //Get the element that holds the earthquakes ( JSONArray )
    JSONArray earthquakes = json.getJSONArray("earthquakes");

    //Loop the Array
    for (int i = 0; i < earthquakes.length(); i++) {
        HashMap<String, String> map = new HashMap<String, String>();
        JSONObject e = earthquakes.getJSONObject(i);

        map.put("id", String.valueOf(i));
        map.put("name", "Earthquake name:" + e.getString("eqid"));
        map.put("magnitude", "Magnitude: " + e.getString("magnitude"));
        mylist.add(map);
    }
} catch (JSONException e) {
    Log.e("log_tag", "Error parsing data " + e.toString());
}

ListAdapter adapter = new SimpleAdapter(this, mylist, R.layout.main,
        new String[]{"name", "magnitude"},
        new int[]{R.id.item_title, R.id.item_subtitle});

setListAdapter(adapter);

Answer 1

As already explained by @pcalcao, you need to decide how you are going to sort the maps (based on what criteria), then implement that sort order in a custom comparator and call Collections.sort with that comparator.

For example, let’s say you want to sort by alphabetical order of names, you would write something like:

Collections.sort(mylist, new Comparator<Map<String, String>>() {

    @Override
    public int compare(Map<String, String> o1, Map<String, String> o2) {
        String name1 = o1.get("name");
        String name2 = o2.get("name");
        if (name1 == null) return -1;
        return name1.compareTo(name2);
    }
});