Question

试着把我自己的音乐播放器包起来，不知道我错在哪里。得到NullPointerException的错误。

我甚至尝试过替换

CREATE TABLE musicList(id integer primary key, path VARCHAR, name VARCHAR);");

与

CREATE TABLE IF NOT EXISTS musicList(id integer primary key, path VARCHAR, name VARCHAR);");

LOGCAT错误：http://lookpic.com/O/i2/1427/zQLBzHqB.png

public class MainActivity extends ActionBarActivity implements AdapterView.OnItemClickListener {

SQLiteDatabase musicDatabase = null;

ListView musicList;

String[] items;

ArrayList<File> mySongs;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    musicList = (ListView) findViewById(R.id.musicList);

        musicDatabase = this.openOrCreateDatabase("MusicDatabase.db", MODE_PRIVATE, null);

        musicDatabase.execSQL("CREATE TABLE musicList(id integer primary key, path VARCHAR, name VARCHAR);");

        File database = getApplicationContext().getDatabasePath("MusicDatabase.db");

        if (database.exists()) {
            Cursor cursor = musicDatabase.rawQuery("SELECT * FROM musicList", null);

            int nameID = cursor.getColumnIndex("name");

            cursor.moveToFirst();

            int i = 0;

            if (cursor != null && cursor.getCount() > 0) {

                do {

                    items[i] = cursor.getString(nameID);

                    i++;

                } while (cursor.moveToNext());

            }

        } else {

            String name, path;
            mySongs = findSongs(Environment.getExternalStorageDirectory());
            for (int i = 0; i < mySongs.size(); i++) {
                items[i] = mySongs.get(i).getName().toString();
                path = mySongs.get(i).toString();
                name = mySongs.get(i).getName().toString();
                musicDatabase.execSQL("INSERT INTO musicList(path,name) VALUES('" + path + "','" + name + "');");
            }

        }
        ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(getApplicationContext(), android.R.layout.simple_list_item_1, items);

        musicList.setAdapter(arrayAdapter);

}

public ArrayList<File> findSongs(File root) {
    ArrayList<File> al = new ArrayList<File>();
    File[] files = root.listFiles();
    for (File singleFile : files) {
        if (singleFile.isDirectory() && !singleFile.isHidden()) {
            al.addAll(findSongs(singleFile));
        } else {
            if (singleFile.getName().endsWith(".mp3") || singleFile.getName().endsWith(".aac"))
                al.add(singleFile);
        }
    }
    return al;
}

@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
    Intent i = new Intent(getApplicationContext(), playActivity.class);
    i.putExtra("SONG_ID", position);
    musicDatabase.close();
    startActivity(i);
}
}

Answer 1

将其替换为您当前的openOrCreateDatabase

 musicDatabase = SQLiteDatabase.openDatabase("MusicDatabase.db", MODE_PRIVATE, SQLiteDatabase.CREATE_IF_NECESSARY);

Android在访问数据库时获取NullPointerException

1 个答案: