保存未知数量数据的最佳方法？

Question

Ok, here I have a quite challenging problem (just to me, of course).

I'm retrieving some data from a MySql db via web services in order to fill an spinner in my app. This spinner shows cities, and this cities should change depending on another spinner's state (which contains countries)

No problem so far. I can retrieve the data, and the spinner changes as it should. My problem is that I don't want my app to connect again and again to retrieve cities information any time the user selects another item from Countries.

And here is my real problem. Ideally I would like to save cities data inside one String array for each country, but considering I don't know how many countries will be loaded from my database my question is: how could I achieve that?

I was thinking that it would be possible by creating a multidimensional array, but I don't know how to create an "array of arrays".

Any ideas?

Thank you very much in advance.

Answer 1

create a proper data structure. And check if it is null then reload data again else perform regular operation. eg refer following getter setter class

public class SpinnerInfoData {
String city="",state="",countries="";

public String getCity() {
    return city;
}

public void setCity(String city) {
    this.city = city;
}

public String getState() {
    return state;
}

public void setState(String state) {
    this.state = state;
}

public String getCountries() {
    return countries;
}

public void setCountries(String countries) {
    this.countries = countries;
}

}

Answer 2

Calling the web service you can store into the DB each country as a JSON string, containing the whole list of cities, for example like this :

{"id": "1", "name": "coutry1", "cities": [{"id": "1", "name": "city1"},{"id": "2", "name": "city2"},{"id": "3", "name": "cityx"}]}

Later making your request on SQLite you can user this JSONObject to create instances of Country

    public class Country extends BaseElement{
        private ArrayList<City> cities;

        // Imagine that for each country we are storing the kind of JSON into the DB
        // {"id": "1", "name": "coutry1", "cities": [{"id": "1", "name": "city1"},{"id": "2", "name": "city2"},{"id": "3", "name": "cityx"}]}
        public Country(String jsonFromDB){
            cities = new ArrayList<City>();
            if(jsonFromDB != null && jsonFromDB.trim().length() > 0){
                try {
                    JSONObject country = new JSONObject(jsonFromDB);
                    setId(country.getInt("id"));
                    setName(country.getString("name"));
                    JSONArray cts = country.getJSONArray("cities");
                    for(int i = 0; i < cts.length() ; i++){
                        cities.add(new City(cts.getJSONObject(i)));
                    }
                } catch (JSONException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }

        public ArrayList<City> getCities(){ 
            return cities;
        }
    }

    public class City extends BaseElement{

        public City(JSONObject jsonFromDB) throws JSONException{
            if(jsonFromDB != null){
                setId(jsonFromDB.getInt("id"));
                setName(jsonFromDB.getString("name"));
            }
        }
    }

    public class BaseElement{
        private int id;
        private String name;

        public int getId() {
            return id;
        }
        public String getName() {
            return name;
        }
        public void setId(int id) {
            this.id = id;
        }
        public void setName(String name) {
            this.name = name;
        }
    }

Then you can use the instances of Country in any kind of adapter for spinners, list, or expandable list....