Question

所以，碰到一堵砖墙。最后确认我的数据库正在处理数据/数据文件夹（它是我创建的静态数据库），似乎应用程序能够找到它，但是当试图从数据库中提取数据以使ListView膨胀时，我遇到了一个我无法解决的错误。（至少这是我假设发生的事情）

08-15 00:11:36.771: E/AndroidRuntime(7000): FATAL EXCEPTION: main
08-15 00:11:36.771: E/AndroidRuntime(7000): java.lang.RuntimeException: Unable to start activity ComponentInfo{table.periodic/table.periodic.elementList}: java.lang.NullPointerException
08-15 00:11:36.771: E/AndroidRuntime(7000):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
08-15 00:11:36.771: E/AndroidRuntime(7000):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
08-15 00:11:36.771: E/AndroidRuntime(7000):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
08-15 00:11:36.771: E/AndroidRuntime(7000):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
08-15 00:11:36.771: E/AndroidRuntime(7000):     at android.os.Handler.dispatchMessage(Handler.java:99)
08-15 00:11:36.771: E/AndroidRuntime(7000):     at android.os.Looper.loop(Looper.java:137)
08-15 00:11:36.771: E/AndroidRuntime(7000):     at android.app.ActivityThread.main(ActivityThread.java:5041)
08-15 00:11:36.771: E/AndroidRuntime(7000):     at java.lang.reflect.Method.invokeNative(Native Method)
08-15 00:11:36.771: E/AndroidRuntime(7000):     at java.lang.reflect.Method.invoke(Method.java:511)
08-15 00:11:36.771: E/AndroidRuntime(7000):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
08-15 00:11:36.771: E/AndroidRuntime(7000):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
08-15 00:11:36.771: E/AndroidRuntime(7000):     at dalvik.system.NativeStart.main(Native Method)
08-15 00:11:36.771: E/AndroidRuntime(7000): Caused by: java.lang.NullPointerException
08-15 00:11:36.771: E/AndroidRuntime(7000):     at table.periodic.elementList.populateListViewFromDatabase(elementList.java:24)
08-15 00:11:36.771: E/AndroidRuntime(7000):     at table.periodic.elementList.onCreate(elementList.java:19)
08-15 00:11:36.771: E/AndroidRuntime(7000):     at android.app.Activity.performCreate(Activity.java:5104)
08-15 00:11:36.771: E/AndroidRuntime(7000):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
08-15 00:11:36.771: E/AndroidRuntime(7000):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
08-15 00:11:36.771: E/AndroidRuntime(7000):     ... 11 more

所以，我可以看到它说我的错误在哪里，但是，当我查看代码时，似乎没有任何错误。

我的DataBaseHelper.class

public class DataBaseHelper extends SQLiteOpenHelper{

    private SQLiteDatabase myDataBase;

    public static final int DATABASE_VERSION = 1;

    private final Context myContext;

    private static String DB_PATH = "data/data/table.periodic/databases/";
    private static String DB_NAME = "elements";
    public static final String DB_TABLE = "elements";
    public static final String KEY_ROWID = "_id";
    public static final String KEY_NAME = "name";
    public static final String KEY_ATOMIC_NUMBER = "atomic number";
    public static final String KEY_ATOMIC_WEIGHT = "atomic weight";
    public static final String KEY_OXIDATION = "oxidation";
    public static final String KEY_SYMBOL = "symbol";
    public static final String KEY_BOILING_POINT = "boiling point";
    public static final String KEY_MELTING_POINT = "melting point";
    public static final String KEY_DENSITY = "density";
    public static final String KEY_ELECTRON_CONFIGURATION = "electron configuration";
    public static final String KEY_STRUCTURE = "structure";
    public static final String KEY_COVALENT_RADIUS = "covalent radius";
    public static final String KEY_ATOMIC_RADIUS = "atomic radius";
    public static final String KEY_VOLUME = "volume";
    public static final String KEY_ION_POTENTIAL = "ion potential";
    public static final String KEY_HEAT_CAPACITY = "heat capacity";
    public static final String KEY_ELECTRONEGATIVITY = "electronegativity";
    public static final String KEY_VAPORATION = "vaporation";
    public static final String KEY_FUSION = "fusion";
    public static final String KEY_ELECTRO_CONDUCTIVITY = "electro conductivity";
    public static final String KEY_THERMAL_CONDUCTIVITY = "thermal conductivity";

    public static final int COL_ROWID = 0;
    public static final int COL_NAME = 1;
    public static final int COL_ATOMIC_NUMBER = 2;
    public static final int COL_ATOMIC_WEIGHT = 3;
    public static final int COL_OXIDATION = 4;
    public static final int COL_SYMBOL = 5;
    public static final int COL_BOILING_POINT = 6;
    public static final int COL_MELTING_POINT = 7;
    public static final int COL_DENSITY = 8;
    public static final int COL_ELECTRON_CONFIGURATION = 9;
    public static final int COL_STRUCTURE = 10;
    public static final int COL_COVALENT_RADIUS = 11;
    public static final int COL_ATOMIC_RADIUS = 12;
    public static final int COL_VOLUME = 13;
    public static final int COL_ION_POTENTIAL = 14;
    public static final int COL_HEAT_CAPACITY = 15;
    public static final int COL_ELECTRONEGATIVITY = 16;
    public static final int COL_VAPORATION = 17;
    public static final int COL_FUSION = 18;
    public static final int COL_ELECTRO_CONDUCTIVITY = 19;
    public static final int COL_THERMAL_CONDUCTIVITY = 20;

    public static final String[] ALL_KEYS = new String[] {KEY_ROWID, KEY_NAME, KEY_ATOMIC_NUMBER, KEY_ATOMIC_WEIGHT,
        KEY_OXIDATION, KEY_SYMBOL, KEY_BOILING_POINT, KEY_MELTING_POINT, KEY_DENSITY, KEY_ELECTRON_CONFIGURATION,
        KEY_STRUCTURE, KEY_COVALENT_RADIUS, KEY_ATOMIC_RADIUS, KEY_VOLUME, KEY_ION_POTENTIAL, KEY_HEAT_CAPACITY,
        KEY_ELECTRONEGATIVITY, KEY_VAPORATION, KEY_FUSION, KEY_ELECTRO_CONDUCTIVITY, KEY_THERMAL_CONDUCTIVITY};

    public DataBaseHelper(Context context) {

        super(context, DB_NAME, null, 1);
        this.myContext = context;

    }

    public void createDataBase() throws IOException {

        boolean dbExists = checkDataBase();

        if (dbExists) {

        } else {

            this.getReadableDatabase();

            try {

                copyDataBase();

            } catch (IOException e) {

                throw new Error("Error copying database");

            }


        }
    }

    private boolean checkDataBase() {

        SQLiteDatabase checkDB = null;

        try {

            String myPath = DB_PATH + DB_NAME;
            checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);

        } catch (SQLiteException e) {

        }

        if (checkDB !=null){

            checkDB.close();

        }

        return checkDB !=null ? true : false;
    }

    private void copyDataBase() throws IOException{

        InputStream myInput = myContext.getAssets().open(DB_NAME);

        String outFileName = DB_PATH + DB_NAME;

        OutputStream myOutput = new FileOutputStream(outFileName);

        byte[] buffer = new byte[1024];
        int length;

        while ((length = myInput.read(buffer))>0){
            myOutput.write(buffer, 0, length);

        }

        myOutput.flush();
        myOutput.close();
        myInput.close();

    }

    public void openDataBase() throws SQLException{
        String myPath = DB_PATH + DB_NAME;
        myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);

    }

    public Cursor getAllRows() {
        String where = null;
        Cursor c = myDataBase.query(true, DB_TABLE, ALL_KEYS, 
                where, null, null, null, null, null, null);

        if (c != null) {
            c.moveToFirst();
        }
        return c;
    }

    public Cursor getRow(long rowId) {
        String where = KEY_ROWID + "=" + rowId;
        Cursor c = myDataBase.query(true, DB_TABLE, ALL_KEYS, 
                where, null, null, null, null, null, null);
        if (c != null) {
            c.moveToFirst();
        }
        return c;
    }

    @Override
        public synchronized void close() {
            if(myDataBase !=null)
                myDataBase.close();

            super.close();
        }

        @Override
        public void onCreate(SQLiteDatabase db) {

        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion){

        }


}

我的elementList.class

public class elementList extends Activity {

    private String[] sElements;
    DataBaseHelper myDB;

    @Override
    public void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        setContentView(R.layout.list_view);
added-->        openDB();
**line 19-->**          populateListViewFromDatabase();

    }

    private void populateListViewFromDatabase() {

  **line 24-->**        Cursor cursor = myDB.getAllRows();

        startManagingCursor(cursor);

        String[] fromFieldNames = new String[]
                {DataBaseHelper.KEY_NAME};

        int[] toViewIDs = new int[]
                {R.id.elListText};

        SimpleCursorAdapter myCursorAdapter =
                new SimpleCursorAdapter(
                        this,
                        R.layout.el_list_item,
                        cursor,
                        fromFieldNames,
                        toViewIDs
                        );

        ListView myList = (ListView) findViewById(R.id.list);
        myList.setAdapter(myCursorAdapter);
    }

    private void openDB() {
        myDB = new DataBaseHelper(this);
        myDB.openDataBase();

    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        closeDB();
    }

    private void closeDB() {
        myDB.close();
    }

}

添加openDB（）后;我现在得到这样的错误。

08-15 03:20:43.252: E/AndroidRuntime(20040): FATAL EXCEPTION: main
08-15 03:20:43.252: E/AndroidRuntime(20040): java.lang.RuntimeException: Unable to start activity ComponentInfo{table.periodic/table.periodic.elementList}: android.database.sqlite.SQLiteException: no such table: elements (code 1): , while compiling: SELECT DISTINCT _id, name, atomic number, atomic weight, oxidation, symbol, boiling point, melting point, density, electron configuration, structure, covalent radius, atomic radius, volume, ion potential, heat capacity, electronegativity, vaporation, fusion, electro conductivity, thermal conductivity FROM elements
08-15 03:20:43.252: E/AndroidRuntime(20040):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
08-15 03:20:43.252: E/AndroidRuntime(20040):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
08-15 03:20:43.252: E/AndroidRuntime(20040):    at android.app.ActivityThread.access$600(ActivityThread.java:141)
08-15 03:20:43.252: E/AndroidRuntime(20040):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
08-15 03:20:43.252: E/AndroidRuntime(20040):    at android.os.Handler.dispatchMessage(Handler.java:99)
08-15 03:20:43.252: E/AndroidRuntime(20040):    at android.os.Looper.loop(Looper.java:137)
08-15 03:20:43.252: E/AndroidRuntime(20040):    at android.app.ActivityThread.main(ActivityThread.java:5041)
08-15 03:20:43.252: E/AndroidRuntime(20040):    at java.lang.reflect.Method.invokeNative(Native Method)
08-15 03:20:43.252: E/AndroidRuntime(20040):    at java.lang.reflect.Method.invoke(Method.java:511)
08-15 03:20:43.252: E/AndroidRuntime(20040):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
08-15 03:20:43.252: E/AndroidRuntime(20040):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
08-15 03:20:43.252: E/AndroidRuntime(20040):    at dalvik.system.NativeStart.main(Native Method)
08-15 03:20:43.252: E/AndroidRuntime(20040): Caused by: android.database.sqlite.SQLiteException: no such table: elements (code 1): , while compiling: SELECT DISTINCT _id, name, atomic number, atomic weight, oxidation, symbol, boiling point, melting point, density, electron configuration, structure, covalent radius, atomic radius, volume, ion potential, heat capacity, electronegativity, vaporation, fusion, electro conductivity, thermal conductivity FROM elements
08-15 03:20:43.252: E/AndroidRuntime(20040):    at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method)
08-15 03:20:43.252: E/AndroidRuntime(20040):    at android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:882)
08-15 03:20:43.252: E/AndroidRuntime(20040):    at android.database.sqlite.SQLiteConnection.prepare(SQLiteConnection.java:493)
08-15 03:20:43.252: E/AndroidRuntime(20040):    at android.database.sqlite.SQLiteSession.prepare(SQLiteSession.java:588)
08-15 03:20:43.252: E/AndroidRuntime(20040):    at android.database.sqlite.SQLiteProgram.<init>(SQLiteProgram.java:58)
08-15 03:20:43.252: E/AndroidRuntime(20040):    at android.database.sqlite.SQLiteQuery.<init>(SQLiteQuery.java:37)
08-15 03:20:43.252: E/AndroidRuntime(20040):    at android.database.sqlite.SQLiteDirectCursorDriver.query(SQLiteDirectCursorDriver.java:44)
08-15 03:20:43.252: E/AndroidRuntime(20040):    at android.database.sqlite.SQLiteDatabase.rawQueryWithFactory(SQLiteDatabase.java:1314)
08-15 03:20:43.252: E/AndroidRuntime(20040):    at android.database.sqlite.SQLiteDatabase.queryWithFactory(SQLiteDatabase.java:1161)
08-15 03:20:43.252: E/AndroidRuntime(20040):    at android.database.sqlite.SQLiteDatabase.query(SQLiteDatabase.java:1073)
08-15 03:20:43.252: E/AndroidRuntime(20040):    at table.periodic.DataBaseHelper.getAllRows(DataBaseHelper.java:158)
08-15 03:20:43.252: E/AndroidRuntime(20040):    at table.periodic.elementList.populateListViewFromDatabase(elementList.java:25)
08-15 03:20:43.252: E/AndroidRuntime(20040):    at table.periodic.elementList.onCreate(elementList.java:20)
08-15 03:20:43.252: E/AndroidRuntime(20040):    at android.app.Activity.performCreate(Activity.java:5104)
08-15 03:20:43.252: E/AndroidRuntime(20040):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
08-15 03:20:43.252: E/AndroidRuntime(20040):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
08-15 03:20:43.252: E/AndroidRuntime(20040):    ... 11 more
08-15 03:20:43.382: D/dalvikvm(20040): GC_CONCURRENT freed 114K, 6% free 4126K/4360K, paused 4ms+60ms, total 171ms
08-15 03:20:43.382: W/SQLiteConnectionPool(20040): A SQLiteConnection object for database 'data/data/table.periodic/databases/elements' was leaked!  Please fix your application to end transactions in progress properly and to close the database when it is no longer needed.

Answer 1

您永远不会致电openDB()，因此myDB为null。

Answer 2

在调用myDB = new DataBaseHelper(this);

之前，您似乎错过了myDB.getAllRows();

从数据库填充ListView时出错

2 个答案: