不传递给DB助手类的Android变量

Question

我有一个应用程序，需要访问一个静态数据库，并运行基于用户输入的查询。我在用

JGil毡/android-sqlite helper

作为我的数据库助手类。我的主要活动有两个旋转器，用户可以使用它来缩小搜索范围。纺丝器分别返回名为mGenre和mDecade的字符串变量。在活动的底部是一个按钮继续进行。当按下按钮时，就会触发一个新的活动，该活动将随机显示一个歌曲标题。变量被传递给新的活动vi，这是putExtra()的意图。新活动接收变量，并在if/else语句中使用它们来决定从DB Helper运行哪个查询。

在DB助手类中，我创建了一个新类的实例，并将其用于设置mGenre和mDecade变量，以便使用rawQuery()的String[] args部分中的变量来运行正确的查询。

下面是当用户点击主活动的按钮时打开的songActivity类：

public class SongActivity extends ActionBarActivity {

    private MyDatabase db;
    private static  final String TAG = "We got ";

    String mGenre;
    String mDecade;


    public String getGenre() {
        return mGenre;
    }

    public String getDecade() {
        return mDecade;
    }

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

        //when activity launches query database using user params

        mGenre = getIntent().getExtras().getString("Genre");
        mDecade = getIntent().getExtras().getString("Decade");
        Log.v(TAG, mGenre);
        Log.v(TAG, mDecade);

        String songTitle = "";
        String songArtist = "";
        String songYear = "";

        TextView mSongTitle = (TextView)findViewById(R.id.songTitle);
        TextView mSongArtist = (TextView)findViewById(R.id.songArtist);
        TextView mSongYear = (TextView)findViewById(R.id.songYear);




        db= new MyDatabase(this);




        if (mGenre.equals("*") && mDecade.equals("*")) {

            Cursor cursor = db.kamikazeSelected();
            cursor.moveToFirst();
            while (!cursor.isAfterLast()) {
                songTitle = cursor.getString(1);
                songArtist = cursor.getString(2);
                songYear = cursor.getString(4);
                Log.i(TAG, String.valueOf(songTitle));
                cursor.moveToNext();
            }
            cursor.close();
            db.close();

        }
        else if (!mGenre.equals("*") && mDecade.equals("*")) {
            Cursor cursor = db.genreSelected();

            cursor.moveToFirst();
            while (!cursor.isAfterLast()) {
                songTitle = cursor.getString(1);
                songArtist = cursor.getString(2);
                songYear = cursor.getString(4);
//                Log.i("cursor", cursor.getString(1));
                Log.i(TAG, String.valueOf(songTitle));
                cursor.moveToNext();
            }
            cursor.close();
            db.close();
        }

        else if (mGenre.equals("*") && !mDecade.equals("*")) {
            Cursor cursor = db.decadeSelected();
            cursor.moveToFirst();
            while (!cursor.isAfterLast()) {
                songTitle = cursor.getString(1);
                songArtist = cursor.getString(2);
                songYear = cursor.getString(4);
                Log.i(TAG, String.valueOf(songTitle));
                cursor.moveToNext();
            }
            cursor.close();
            db.close();
        }

        else if (!mGenre.equals("*") && !mDecade.equals("*")) {
            Cursor cursor = db.bothSelected();
            cursor.moveToFirst();
            while (!cursor.isAfterLast()) {
                songTitle = cursor.getString(1);
                songArtist = cursor.getString(2);
                songYear = cursor.getString(4);
                Log.i(TAG, String.valueOf(songTitle));
                cursor.moveToNext();
            }
            cursor.close();
            db.close();
        }
        mSongTitle.setText(songTitle);
        mSongArtist.setText(songArtist);
        mSongYear.setText(songYear);


    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }


}

下面是数据库助手类：

public class MyDatabase extends SQLiteAssetHelper {

    private static  final String TAG = "Variable for query is ";
    private static final String DATABASE_NAME = "mankiniDB.sqlite";
    private static final int DATABASE_VERSION = 1;






    public MyDatabase(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }


    SongActivity mSongActivity = new SongActivity();
    String mGenre = mSongActivity.getGenre();
    String mDecade = mSongActivity.getDecade();





    public Cursor kamikazeSelected() {
        SQLiteDatabase db = getReadableDatabase();

        Cursor cursor =db.rawQuery("SELECT * FROM songList ORDER BY random() limit 1", null);

        return cursor;
    }

    public Cursor genreSelected() {
        SQLiteDatabase db = getReadableDatabase();

        Cursor cursor =db.rawQuery("SELECT * FROM songList WHERE Genre = ? ORDER BY random() limit 1", new String[] {mGenre});

        return cursor;
    }

    public Cursor decadeSelected() {
        SQLiteDatabase db = getReadableDatabase();

        Cursor cursor =db.rawQuery("SELECT * FROM songList WHERE Decade = ? ORDER BY random() limit 1", new String[] {mDecade});
        return cursor;
    }

    public Cursor bothSelected() {

        SQLiteDatabase db = getReadableDatabase();

        Cursor cursor =db.rawQuery("SELECT * FROM songList WHERE Decade = ? AND Genre = ? ORDER BY random() limit 1", new String[] {mDecade, mGenre});

        return cursor;
    }

}

下面是LogCat错误堆栈跟踪：

03-19 21:35:54.256    1751-1751/tomschinler.thegreatman_kiniskamikazekaraoke I/SQLiteAssetHelper﹕ successfully opened database mankiniDB.sqlite
03-19 21:35:54.260    1751-1751/tomschinler.thegreatman_kiniskamikazekaraoke D/AndroidRuntime﹕ Shutting down VM
03-19 21:35:54.264    1751-1751/tomschinler.thegreatman_kiniskamikazekaraoke W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0xa4b61648)
03-19 21:35:54.276    1751-1751/tomschinler.thegreatman_kiniskamikazekaraoke E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.RuntimeException: Unable to start activity ComponentInfo{tomschinler.thegreatman_kiniskamikazekaraoke/tomschinler.thegreatman_kiniskamikazekaraoke.SongActivity}: java.lang.IllegalArgumentException: the bind value at index 1 is null
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
            at android.app.ActivityThread.access$600(ActivityThread.java:141)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:5103)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:525)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.IllegalArgumentException: the bind value at index 1 is null
            at android.database.sqlite.SQLiteProgram.bindString(SQLiteProgram.java:164)
            at android.database.sqlite.SQLiteProgram.bindAllArgsAsStrings(SQLiteProgram.java:200)
            at android.database.sqlite.SQLiteDirectCursorDriver.query(SQLiteDirectCursorDriver.java:47)
            at android.database.sqlite.SQLiteDatabase.rawQueryWithFactory(SQLiteDatabase.java:1314)
            at android.database.sqlite.SQLiteDatabase.rawQuery(SQLiteDatabase.java:1253)
            at tomschinler.thegreatman_kiniskamikazekaraoke.MyDatabase.genreSelected(MyDatabase.java:50)
            at tomschinler.thegreatman_kiniskamikazekaraoke.SongActivity.onCreate(SongActivity.java:82)
            at android.app.Activity.performCreate(Activity.java:5133)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
            at android.app.ActivityThread.access$600(ActivityThread.java:141)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:5103)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:525)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
            at dalvik.system.NativeStart.main(Native Method)

问题是，无论我做什么，或者在哪里设置变量，数据库助手类都会接收和空变量，从而产生一个空参数。我需要用户的输入，完成查询。但它总是空的。请帮我看看我错过了什么。

Answer 1

您不应该自己创建一个Activity实例(new SongActivity())，这是行不通的。您需要与现有的Activity实例进行通信，例如将其传递给DB处理程序，尽管不建议这样做。最好的方法是只传递所需的数据，这样您的活动和DB处理程序就可以解耦。

例如：

public Cursor genreSelected(final String genre) {
    SQLiteDatabase db = getReadableDatabase();
    Cursor cursor =db.rawQuery("SELECT * FROM songList WHERE Genre = ? ORDER BY random() limit 1", new String[] {genre});
    return cursor;
}

考虑将查询字符串作为private static final在您的类上移动，这使得从几个部分访问它们和/或修改它们更容易。

而且，您对Cursor的处理也很奇怪。这是正确的方法：

    try {
        while (cursor.moveToNext()) {
            songTitle = cursor.getString(1);
            songArtist = cursor.getString(2);
            songYear = cursor.getString(4);
            Log.i(TAG, String.valueOf(songTitle));
        }
    } finally {
        cursor.close()
    }

Answer 2

public class DBHelper extends SQLiteOpenHelper {

    private final static String DATABASE_NAME = "UserInfo.db";

    public DBHelper(Context context) {
        super(context, DATABASE_NAME, null, 1);
    }

    @Override
    public void onCreate(SQLiteDatabase sqLiteDatabase) {

        String CREATE_TABLE =
                "CREATE TABLE " + UserProfile.Users.TABLE_NAME + " (" +
                        UserProfile.Users._ID + " INTEGER PRIMARY KEY," +
                        UserProfile.Users.COLUMN_USERNAME + " TEXT," +
                        UserProfile.Users.COLUMN_DOB + " TEXT," +
                        UserProfile.Users.COLUMN_GENDER + " TEXT," +
                        UserProfile.Users.COLUMN_PASSWORD + " TEXT )";

        sqLiteDatabase.execSQL(CREATE_TABLE);
    }

    @Override
    public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {

    }

    public long addInfo(String username, String password){

        SQLiteDatabase sqLiteDatabase = getWritableDatabase();

        ContentValues contentValues = new ContentValues();
        contentValues.put(UserProfile.Users.COLUMN_USERNAME, username);
        contentValues.put(UserProfile.Users.COLUMN_PASSWORD, password);

        long rowId = sqLiteDatabase.insert(UserProfile.Users.TABLE_NAME, null, contentValues);

        return rowId;
    }

    public int updateInfo(String userId, String userName, String password, String dob, String gender){

        SQLiteDatabase sqLiteDatabase = getWritableDatabase();

        ContentValues values = new ContentValues();
        values.put(UserProfile.Users.COLUMN_USERNAME, userName);
        values.put(UserProfile.Users.COLUMN_PASSWORD, password);
        values.put(UserProfile.Users.COLUMN_GENDER, gender);
        values.put(UserProfile.Users.COLUMN_DOB, dob);

        String selection = UserProfile.Users._ID + " = ?";
        String args[] = {userId};

        int count = sqLiteDatabase.update(UserProfile.Users.TABLE_NAME, values, selection, args);

        return count;
    }

    public ArrayList readAllInfo(){

        SQLiteDatabase sqLiteDatabase = getReadableDatabase();

        String[] projection = {

                UserProfile.Users._ID,
                UserProfile.Users.COLUMN_USERNAME,
                UserProfile.Users.COLUMN_DOB,
                UserProfile.Users.COLUMN_GENDER,
                UserProfile.Users.COLUMN_PASSWORD
        };

        String sortOrder = UserProfile.Users._ID + " DESC";

        Cursor cursor = sqLiteDatabase.query(
                UserProfile.Users.TABLE_NAME,
                projection,
                null,
                null,
                null,
                null,
                sortOrder
        );

        ArrayList<User> list = new ArrayList<>();

        if (cursor.getCount() > 0){

            while(cursor.moveToNext()){

                User newUser = new User();

                int id = cursor.getInt(cursor.getColumnIndexOrThrow(UserProfile.Users._ID));
                String user = cursor.getString(cursor.getColumnIndexOrThrow(UserProfile.Users.COLUMN_USERNAME));
                String date = cursor.getString(cursor.getColumnIndexOrThrow(UserProfile.Users.COLUMN_DOB));
                String gen = cursor.getString(cursor.getColumnIndexOrThrow(UserProfile.Users.COLUMN_GENDER));
                String pass = cursor.getString(cursor.getColumnIndexOrThrow(UserProfile.Users.COLUMN_PASSWORD));

                newUser.setUserId(id+"");
                newUser.setUserName(user);
                newUser.setDateOfBirth(date);
                newUser.setGender(gen);
                newUser.setPassword(pass);

                list.add(newUser);
            }
        }

        return list;
    }

    public ArrayList readAllInfo(String userId, String userName){

        String selection;
        String[] args = {""};

        if(userId == null){

            selection = UserProfile.Users.COLUMN_USERNAME + " LIKE ?";
            args[0] = userName;
        }
        else
        {
            selection = UserProfile.Users._ID + " = ?";
            args[0] = userId;
        }

        SQLiteDatabase sqLiteDatabase = getReadableDatabase();

        String[] projection = {

                UserProfile.Users._ID,
                UserProfile.Users.COLUMN_USERNAME,
                UserProfile.Users.COLUMN_DOB,
                UserProfile.Users.COLUMN_GENDER,
                UserProfile.Users.COLUMN_PASSWORD
        };



        String sortOrder = UserProfile.Users._ID + " DESC";

        Cursor cursor = sqLiteDatabase.query(
                UserProfile.Users.TABLE_NAME,
                projection,
                selection,
                args,
                null,
                null,
                sortOrder
        );

        ArrayList<User> list = new ArrayList<>();

        if (cursor.getCount() > 0){

            while(cursor.moveToNext()){

                User newUser = new User();

                int id = cursor.getInt(cursor.getColumnIndexOrThrow(UserProfile.Users._ID));
                String user = cursor.getString(cursor.getColumnIndexOrThrow(UserProfile.Users.COLUMN_USERNAME));
                String date = cursor.getString(cursor.getColumnIndexOrThrow(UserProfile.Users.COLUMN_DOB));
                String gen = cursor.getString(cursor.getColumnIndexOrThrow(UserProfile.Users.COLUMN_GENDER));
                String pass = cursor.getString(cursor.getColumnIndexOrThrow(UserProfile.Users.COLUMN_PASSWORD));

                newUser.setUserId(id+"");
                newUser.setUserName(user);
                newUser.setDateOfBirth(date);
                newUser.setGender(gen);
                newUser.setPassword(pass);

                list.add(newUser);
            }
        }

        return list;
    }

    public int deleteInfo(String username){

        SQLiteDatabase sqLiteDatabase = getReadableDatabase();

        String selection = UserProfile.Users._ID + " = ?";
        String[] args = {username};

        int deletedRows = sqLiteDatabase.delete(UserProfile.Users.TABLE_NAME, selection, args);

        return deletedRows;
    }
}