java - 如何让我的 ExpandableListView 等待加载，直到填充我的 HashMap？

Question

我在 android 中使用 ExpandableListView，但问题是我的代码在填充 HashMap 之前加载了它，因此它显示了一个空的 ListView。

我加载 ExpandableListView 的 fragment 是这个:

package com.example.arno.eventaris.Fragment;


import android.app.Activity;
import android.app.DialogFragment;
import android.net.wifi.WifiConfiguration;
import android.os.Bundle;
import android.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;




import com.example.arno.eventaris.Activity.MainActivity;
import com.example.arno.eventaris.Error.ErrorJason;

import com.example.arno.eventaris.Expandable.ExpandableListAdapter;
import com.example.arno.eventaris.R;


import android.widget.ExpandableListView;
import android.widget.ExpandableListView.OnChildClickListener;
import android.widget.ExpandableListView.OnGroupClickListener;
import android.widget.ExpandableListView.OnGroupCollapseListener;
import android.widget.ExpandableListView.OnGroupExpandListener;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import android.widget.Toast;



/**
 * A simple {@link Fragment} subclass.
 */
public class HomeFragment extends Fragment {

    private OnHomeFragmentInteractionListener mListener;
    private View view;

    private ExpandableListAdapter listAdapter;
    private ExpandableListView expListView;
    private List<String> listDataHeader;
    private HashMap<String, List<String>> listDataChild;
    private HashMap<String,HashMap<String,String>> events;

    public HomeFragment() {
        // Required empty public constructor
    }




    @Override
    public View onCreateView (LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        ((MainActivity)getActivity()).populateEvents();

        events = ((MainActivity)getActivity()).getEvents();

        view=inflater.inflate(R.layout.fragment_home, container, false);


        // get the listview
        expListView = (ExpandableListView) view.findViewById(R.id.lvExp);

        // preparing list data
        prepareListData();

        listAdapter = new ExpandableListAdapter(getActivity(), listDataHeader, listDataChild);

        // setting list adapter
        expListView.setAdapter(listAdapter);



        return view;
    }



    /*
     * Preparing the list data
     */
    private void prepareListData() {



        listDataHeader = new ArrayList<String>();
        listDataChild = new HashMap<String, List<String>>();

        // Adding child data
        listDataHeader.add("A");
        listDataHeader.add("B");
        listDataHeader.add("C");
        listDataHeader.add("D");
        listDataHeader.add("E");
        listDataHeader.add("F");
        listDataHeader.add("G");
        listDataHeader.add("H");
        listDataHeader.add("I");
        listDataHeader.add("J");
        listDataHeader.add("K");
        listDataHeader.add("L");
        listDataHeader.add("M");
        listDataHeader.add("N");
        listDataHeader.add("O");
        listDataHeader.add("P");
        listDataHeader.add("Q");
        listDataHeader.add("R");
        listDataHeader.add("S");
        listDataHeader.add("T");
        listDataHeader.add("U");
        listDataHeader.add("V");
        listDataHeader.add("W");
        listDataHeader.add("X");
        listDataHeader.add("Y");
        listDataHeader.add("Z");
        listDataHeader.add("*");

        // Adding child data
        List<String> A = new ArrayList<String>();
        List<String> B = new ArrayList<String>();
        List<String> C = new ArrayList<String>();
        List<String> D = new ArrayList<String>();
        List<String> E = new ArrayList<String>();
        List<String> F = new ArrayList<String>();
        List<String> G = new ArrayList<String>();
        List<String> H = new ArrayList<String>();
        List<String> I = new ArrayList<String>();
        List<String> J = new ArrayList<String>();
        List<String> K = new ArrayList<String>();
        List<String> L = new ArrayList<String>();
        List<String> M = new ArrayList<String>();
        List<String> N = new ArrayList<String>();
        List<String> O = new ArrayList<String>();
        List<String> P = new ArrayList<String>();
        List<String> Q = new ArrayList<String>();
        List<String> R = new ArrayList<String>();
        List<String> S = new ArrayList<String>();
        List<String> T = new ArrayList<String>();
        List<String> U = new ArrayList<String>();
        List<String> V = new ArrayList<String>();
        List<String> W = new ArrayList<String>();
        List<String> X = new ArrayList<String>();
        List<String> Y = new ArrayList<String>();
        List<String> Z = new ArrayList<String>();
        List<String> anders = new ArrayList<String>();

        for(String key : events.keySet())
        {
            String eersteLetter = Character.toString(key.charAt(0));

            switch(eersteLetter)
            {
                case "a" : A.add(key);
                    break;
                case "b" : B.add(key);
                    break;
                case "c" : C.add(key);
                    break;
                case "d" : D.add(key);
                    break;
                case "e" : E.add(key);
                    break;
                case "f" : F.add(key);
                    break;
                case "g" : G.add(key);
                    break;
                case "h" : H.add(key);
                    break;
                case "i" : I.add(key);
                    break;
                case "j" : J.add(key);
                    break;
                case "k" : K.add(key);
                    break;
                case "l" : L.add(key);
                    break;
                case "m" : M.add(key);
                    break;
                case "n" : N.add(key);
                    break;
                case "o" : O.add(key);
                    break;
                case "p" : P.add(key);
                    break;
                case "q" : Q.add(key);
                    break;
                case "r" : R.add(key);
                    break;
                case "s" : S.add(key);
                    break;
                case "t" : T.add(key);
                    break;
                case "u" : U.add(key);
                    break;
                case "v" : V.add(key);
                    break;
                case "w" : W.add(key);
                    break;
                case "x" : X.add(key);
                    break;
                case "y" : Y.add(key);
                    break;
                case "z" : Z.add(key);
                    break;
                default :  anders.add(key);
                    break;

            }
        }

        listDataChild.put(listDataHeader.get(0), A); // Header, Child data
        listDataChild.put(listDataHeader.get(1), B);
        listDataChild.put(listDataHeader.get(2), C);
        listDataChild.put(listDataHeader.get(3), D);
        listDataChild.put(listDataHeader.get(4), E);
        listDataChild.put(listDataHeader.get(5), F);
        listDataChild.put(listDataHeader.get(6), G);
        listDataChild.put(listDataHeader.get(7), H);
        listDataChild.put(listDataHeader.get(8), I);
        listDataChild.put(listDataHeader.get(9), J);
        listDataChild.put(listDataHeader.get(10), K);
        listDataChild.put(listDataHeader.get(11), L);
        listDataChild.put(listDataHeader.get(12), M);
        listDataChild.put(listDataHeader.get(13), N);
        listDataChild.put(listDataHeader.get(14), O);
        listDataChild.put(listDataHeader.get(15), P);
        listDataChild.put(listDataHeader.get(16), Q);
        listDataChild.put(listDataHeader.get(17), R);
        listDataChild.put(listDataHeader.get(18), S);
        listDataChild.put(listDataHeader.get(19), T);
        listDataChild.put(listDataHeader.get(20), U);
        listDataChild.put(listDataHeader.get(21), V);
        listDataChild.put(listDataHeader.get(22), W);
        listDataChild.put(listDataHeader.get(23), X);
        listDataChild.put(listDataHeader.get(24), Y);
        listDataChild.put(listDataHeader.get(25), Z);
        listDataChild.put(listDataHeader.get(26), anders);

    }


    @Override
    public void onAttach(Activity activity)
    {
        super.onAttach(activity);
        try{
            mListener = (OnHomeFragmentInteractionListener) activity;

        }
        catch (ClassCastException e)
        {
            throw new ClassCastException(activity.toString() + "must implement OnFragmentInteractionListener");
        }
    }

    @Override
    public void onDetach()
    {
        super.onDetach();
        mListener = null;
    }



    public interface OnHomeFragmentInteractionListener
    {



    }


}

问题是我用于 ExpandableListView 的数据来自于我放入 MaintActivity.Java 中的 HashMap 中的 JSON 文件。

现在它会遍历我的整个 HomeFragment.java 代码直到最后，并且只有当发生这种情况时它才会开始执行这行代码:

((MainActivity)getActivity()).populateEvents();

我已将其放在 onCreateView 方法的开头。我跟踪了调试器，所以我知道他遵循的顺序不是我想要的。有没有办法确保他在继续创建 ExpendableListView 之前执行这行代码？

Answer 1

我建议您使用AsyncTask来填充数据。您将在 doInBackground() 方法中加载数据，然后在 onPostExecute() 中创建适配器。

1) 创建 AsyncTask 类:

private class PopulatingTask extends AsyncTask<Void, Void, Boolean> {

         private ProgressDialog dialog;
         private MainActivity activity;

        public PopulatingTask (MainActivity activity) {
            this.activity = activity;
            dialog = new ProgressDialog(activity);
        }

        @Override
        protected void onPreExecute() {
            this.dialog.setMessage("Loading data...");
            this.dialog.show();
        }

        @Override
        protected Boolean doInBackground(Void... args) {
            try{    

                activity.populateEvents();

                events = activity.getEvents();

                // preparing list data
                prepareListData();

                return true;

             } catch (Exception e){
                Log.e("tag", "error", e);
                return false;
             }
          }

        @Override
        protected void onPostExecute(Boolean success) {

            listAdapter = new ExpandableListAdapter(activity, listDataHeader, listDataChild);

            // setting list adapter
            expListView.setAdapter(listAdapter);

            // dismiss the dialog
            if (dialog.isShowing()) {
                dialog.dismiss();
            }

            if (success) {
                Toast.makeText(activity, "OK", Toast.LENGTH_LONG).show();
            } else {
                Toast.makeText(activity, "Error", Toast.LENGTH_LONG).show();
            }
        }
    }

2) 将您的 onCreateView() 方法更改为:

@Override
    public View onCreateView (LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        view=inflater.inflate(R.layout.fragment_home, container, false);

        // get the listview
        expListView = (ExpandableListView) view.findViewById(R.id.lvExp);

        // start the asyncTask
        new PopulatingTask((MainActivity)getActivity()).execute();

        return view;
    }