将新项目添加到expandablelistview

Question

我正在尝试创建一个Android应用程序，该应用程序获取有关专辑的信息并将其显示在可扩展的列表视图中。艺术家的姓名将显示为父项，当选择艺术家时，该艺术家的专辑将显示为孩子。 到目前为止，通过初始化MyExpandableListAdapter类中的字符串，我已经能够使列表工作。 但是，我希望能够按一个按钮并将新视图添加到包含信息的列表中。

这是我的代码：

package droid.musiclibrary;

/**
 * Some code taken from:
 * http://www.dreamincode.net/forums/topic/270612-how-to-get-started-with-expandablelistview/ 
 */

import java.util.ArrayList;
import java.util.List;
import android.app.Activity;
import android.app.ExpandableListActivity;
import android.app.ListActivity;
import android.content.Context;
import android.content.Intent;
import android.database.DataSetObserver;
import android.os.Bundle;
import android.util.Log;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.ArrayAdapter;
import android.widget.BaseAdapter;
import android.widget.BaseExpandableListAdapter;
import android.widget.EditText;
import android.widget.ExpandableListAdapter;
import android.widget.ExpandableListView;
import android.widget.ListAdapter;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.Toast;

public class AddContent extends Activity {

    private Spinner spinArtist, spinGenre;
    private EditText addArtist, addGenre, addTitle, addYear;
    private ArrayAdapter<String> adapterArtist, adapterGenre;
    private ArrayList<String> artists = new ArrayList<String>();
    private ArrayList<String> genres = new ArrayList<String>();
    private ArrayList<String> albums = new ArrayList<String>();
    private ArrayList<String> albumList = new ArrayList<String>();
    List<List<String>> albumArray = new ArrayList<List<String>>();
    private ExpandableListView expList;
    private MyExpandableListAdapter expAdapter;

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        getActionBar().setDisplayHomeAsUpEnabled(true);
        setContentView(R.layout.add_content);

        expList = (ExpandableListView) findViewById(R.id.artistList);
        expAdapter = new MyExpandableListAdapter(this);
        expList.setAdapter(expAdapter);
    }

    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case android.R.id.home:
                // This is called when the Home (Up) button is pressed
                // in the Action Bar.
                Intent parentActivityIntent = new Intent(this, MainActivity.class);
                parentActivityIntent.addFlags(
                        Intent.FLAG_ACTIVITY_CLEAR_TOP |
                        Intent.FLAG_ACTIVITY_NEW_TASK);
                startActivity(parentActivityIntent);
                finish();
                return true;
        }
        return super.onOptionsItemSelected(item);
    }

    public AddContent() {

    }

    public void addArtist(View view) {
        spinArtist = (Spinner) findViewById(R.id.spinArtist);
        addArtist = (EditText) findViewById(R.id.txtAddArtist);
        if(addArtist.getText().toString().trim().equals(""))
        {
            Context context = getApplicationContext();
            CharSequence text = "You need to enter an artist.";
            int duration = Toast.LENGTH_SHORT;

            Toast toast = Toast.makeText(context, text, duration);
            toast.show();
        }
        else
            artists.add(addArtist.getText().toString());

        adapterArtist = new ArrayAdapter<String>(this,
                android.R.layout.simple_spinner_dropdown_item, artists);
        adapterArtist.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        spinArtist.setAdapter(adapterArtist);
        addArtist.setText("");
    }

    public void addGenre(View view) {
        spinGenre = (Spinner) findViewById(R.id.spinGenre);
        addGenre = (EditText) findViewById(R.id.txtAddGenre);
        if(addGenre.getText().toString().trim().equals(""))
        {
            Context context = getApplicationContext();
            CharSequence text = "You need to enter a genre.";
            int duration = Toast.LENGTH_SHORT;

            Toast toast = Toast.makeText(context, text, duration);
            toast.show();
        }
        else
            genres.add(addGenre.getText().toString());

        adapterGenre = new ArrayAdapter<String>(this,
                android.R.layout.simple_spinner_dropdown_item, genres);
        adapterGenre.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        spinGenre.setAdapter(adapterGenre);
        addGenre.setText("");
    }

    public void addAlbum(View view) {

        addTitle = (EditText) findViewById(R.id.txtAddTitle);
        addYear = (EditText) findViewById(R.id.txtAddYear);

        if(addTitle.getText().toString().trim().equals(""))
        {
            Context context = getApplicationContext();
            CharSequence text = "You need to enter a title.";
            int duration = Toast.LENGTH_SHORT;

            Toast toast = Toast.makeText(context, text, duration);
            toast.show();
        }
        else if(spinArtist.getSelectedItem().toString().trim().equals(""))
        {
            Context context = getApplicationContext();
            CharSequence text = "You need to select an artist.";
            int duration = Toast.LENGTH_SHORT;

            Toast toast = Toast.makeText(context, text, duration);
            toast.show();
        }
        else if(spinGenre.getSelectedItem().toString().trim().equals(""))
        {
            Context context = getApplicationContext();
            CharSequence text = "You need to select a genre.";
            int duration = Toast.LENGTH_SHORT;

            Toast toast = Toast.makeText(context, text, duration);
            toast.show();
        }
        else if(addYear.getText().toString().trim().equals(""))
        {
            Context context = getApplicationContext();
            CharSequence text = "You need to enter a year.";
            int duration = Toast.LENGTH_SHORT;

            Toast toast = Toast.makeText(context, text, duration);
            toast.show();
        }
        else
        {
            albums.add(addTitle.getText().toString().trim());           
        }

    }

    public class MyExpandableListAdapter extends BaseExpandableListAdapter {
        private Context context;

        String[] groups = {"Silverstein"};
        String[][] children = {{"Discovering the Waterfront"}};

        public MyExpandableListAdapter(Context context) {
            this.context = context;
        }

        public Object getChild(int groupPosition, int childPosition) {
            return children[groupPosition][childPosition];
        }

        public long getChildId(int groupPosition, int childPosition) {
            return childPosition;
        }

        public int getChildrenCount(int groupPosition) {
            return children[groupPosition].length;
        }

        public TextView getGenericView() {
            // Layout parameters for the ExpandableListView
            AbsListView.LayoutParams lp = new AbsListView.LayoutParams(
                    ViewGroup.LayoutParams.FILL_PARENT, 64);

            TextView tv = new TextView(this.context);
            tv.setLayoutParams(lp);

            // Center the text vertically
            tv.setGravity(Gravity.CENTER_VERTICAL | Gravity.LEFT);
            // Set the text starting position
            tv.setPadding(45, 0, 0, 0);
            return tv;
        }

        public View getChildView(int groupPosition, int childPosition, boolean isLastChild,
                View convertView, ViewGroup parent) {

            TextView textView = getGenericView();
            textView.setText(getChild(groupPosition, childPosition).toString());
            return textView;
        }

        public Object getGroup(int groupPosition) {
            return groups[groupPosition];
        }

        public int getGroupCount() {
                return groups.length;
        }

        public long getGroupId(int groupPosition) {
            return groupPosition;
        }

        public View getGroupView(int groupPosition, boolean isExpanded, View convertView,
                ViewGroup parent) {

            TextView textView = getGenericView();
            textView.setText(getGroup(groupPosition).toString());
            return textView;
        }

        public boolean isChildSelectable(int groupPosition, int childPosition) {
            return true;
        }

        public boolean hasStableIds() {
            return true;
        }
    }

    /*public void setArtist(ArrayList<String> artist) {
        this.artists = artist;
    }

    public ArrayList<String> getArtist() {
        return artist;
    }

    public void setAlbum(ArrayList<String> album) {
        this.albums = album;
    }

    public ArrayList<String> getAlbum() {
        return albums;
    }

    /**
     * This will actually be used to sort the added content. 
     * For example, when sorting by artist, the parent will be the artist's name
     * and the child entries will be the albums by that artist.
     * This will probably have to moved to a separate class (Sort.java???)
     */
    /*public void addItem(ExpandListChild item, ExpandListParent group) {
        if(!artistList.contains(group)) {
            artistList.add((group));
        }
        int index = artistList.indexOf(group);
        ArrayList<ExpandListChild> ch = artistList.get(index).getItems();
        ch.add(item);
        artistList.get(index).setItems(ch);
    }

    public Object getChild(int parentPosition, int childPosition) {
        ArrayList<ExpandListChild> chList = artistList.get(parentPosition).getItems();
        return chList.get(childPosition);
    }

    public long getChildId(int parentPosition, int childPosition) {
        return childPosition;
    }*/
}

有什么方法可以将艺术家和专辑ArrayList添加到MyExpandableListAdpter类的String []中？ 我尝试了许多不同的方法，每次我得到NullPointerException。

任何帮助将不胜感激，我已经花费了数小时寻找答案。

Answer 1

放入SimpleExpandableListAdapter并维护对组（父）和子数据对象的引用。

然后就这么简单：

mChildData.get(groupIndex).get(childIndex).put(...);
mListAdapter.notifyDataSetChanged();