Question

我是android编程的新手，并且还在了解它的概念，我正在构建一个应用程序，它将从在线数据库中获取一些数据并将其存储在ArrayList＆gt;输入，然后我将显示数据，

我已成功从数据库中获取数据并在ListView上成功显示，现在我想根据其日期对数据进行排序（在hashmap中存储了一个日期值），

我已经阅读了如何在这些问题中做到这一点：

How to sort data of ArrayList of hashmap on The Basis of Date

我没有真正理解这个概念，但仍然不知道如何使用我当前的代码。希望你能帮我解决我的代码，

这是我的代码：

public class Notification extends Activity {

userSessionManager session;
String Username, clickedId, clickedTitle, toastMessage;
String urlUpdateGroupConfirmation, urlGetNotif;
JSONParser jsonParser;
ProgressDialog pd;
JSONArray jsonArray = null;
private ArrayList<HashMap<String, String>> whatsNew;

@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.notification);

    getActionBar().setDisplayShowHomeEnabled(false);
    sessionAndDeclaration();
    new AttemptParseNotification().execute();
}

private void sessionAndDeclaration() {
    // TODO Auto-generated method stub
    session = new userSessionManager(getApplicationContext());
    HashMap<String, String> user = session.getUserDetails();
    Username = user.get(userSessionManager.KEY_USERNAME);
    myIP ip = new myIP();
    String publicIp = ip.getIp();
    String thisPhp = "viewMyNotification.php";
    String updateGConf = "doUpdateGroupDetail.php";

    urlGetNotif = publicIp + thisPhp;
    urlUpdateGroupConfirmation = publicIp + updateGConf;
    jsonParser = new JSONParser();
    whatsNew = new ArrayList<HashMap<String, String>>();

}

class myMapComparator implements Comparator<Map<String, String>> {

    @Override
    public int compare(Map<String, String> lhs, Map<String, String> rhs) {
        // TODO Auto-generated method stub
        DateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

        try {
            return df.parse(lhs.get("date")).compareTo(
                    df.parse(rhs.get("date")));

        } catch (ParseException e) {
            throw new IllegalArgumentException(e);
        }
    }

}

class AttemptParseNotification extends AsyncTask<Void, Void, Boolean> {

    @Override
    protected void onPreExecute() {
        // TODO Auto-generated method stub
        super.onPreExecute();
        pd = new ProgressDialog(Notification.this);
        pd.setIndeterminate(false);
        pd.setCancelable(true);
        pd.setMessage("Loading...");
        pd.show();
    }

    @Override
    protected Boolean doInBackground(Void... arg0) {
        // TODO Auto-generated method stub
        int success = 0;
        try {
            List<NameValuePair> params = new ArrayList<NameValuePair>();
            params.add(new BasicNameValuePair("Username", Username));
            Log.d("Request!", "Passing Username to server");
            JSONObject json = jsonParser.makeHttpRequest(urlGetNotif,
                    "POST", params);
            success = json.getInt("success");
            if (success == 1) {
                Log.d("Response", "Getting todays");
                jsonArray = json.getJSONArray("array");
                try {
                    for (int i = 0; i < jsonArray.length(); i++) {
                        JSONObject c = jsonArray.getJSONObject(i);
                        String newId = c.getString("id");
                        String newType = c.getString("type");
                        String newTitle = c.getString("title");
                        String newDisplayed = newTitle + "(" + newType
                                + ")";
                        String newDate = c.getString("date");
                        HashMap<String, String> map = new HashMap<String, String>();
                        map.put("id", newId);
                        map.put("title", newTitle);
                        map.put("date", newDate);
                        map.put("type", newType);
                        map.put("displayed", newDisplayed);
                        whatsNew.add(map);
                        Collections.sort(whatsNew, new myMapComparator());

                    }
                } catch (JSONException e) {
                    e.printStackTrace();
                }

            }
        } catch (JSONException e) {
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onPostExecute(Boolean result) {
        // TODO Auto-generated method stub
        super.onPostExecute(result);
        pd.dismiss();
        if (whatsNew.size() > 0) {

            viewNews();
        } else {
            Toast.makeText(getBaseContext(), "No new notification",
                    Toast.LENGTH_LONG).show();
        }
    }

}

public void viewNews() {
    // TODO Auto-generated method stub
    ListView lv = (ListView) findViewById(R.id.lv_notif);
    ListAdapter adapter = new SimpleAdapter(this, whatsNew,
            R.layout.notificationlist_item, new String[] { "title", "type",
                    "date" }, new int[] { R.id.title_notif,
                    R.id.type_notif, R.id.date_notif });
    lv.setAdapter(adapter);

}
}

Answer 1

我建议使用TreeSet代替Collections.sort，

这是粗略的例子，

public static Set<HashMap<String, String>> mySet = new TreeSet<>(new Comparator<HashMap<String, String>>() {
        @Override
        public int compare(HashMap<String, String> o1, HashMap<String, String> o2) {
            DateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

            try {
                return df.parse(o1.get("date")).compareTo(
                        df.parse(o2.get("date")));

            } catch (ParseException e) {
                throw new IllegalArgumentException(e);
            }       }
    });

b / w Collections.sort和TreeSet之间的区别在于TreeSet始终对您的数据进行排序，而Collections.sort()方法在您调用方法时对其进行排序你的套装。

例如，如果你在其中添加数据，即mySet.add(yourData);，它将按排序顺序添加。

Answer 2

在将所有数据添加到“whatsNew”列表的循环之后，您需要调用比较器对列表进行排序。

在“return null”之前将此行添加到“doInBackground”...

Collections.sort(whatsNew, new myMapComparator());

（旁注：您可能已经知道，在Java中，惯例是以大写字母开始一个类名称）

Sort ArrayList <hashmap <string，string>＆gt;基于datetime </hashmap <string，string>

2 个答案: