使用游标从数据库获取数据

Question

我正在尝试从数据库中获取数据。我在Java类中做过吸气剂，然后将其发送给另一个Java类。外观如下：

DatabaseHelper

public class DatabaseHelper extends SQLiteOpenHelper {

    private static final String TAG = "DatabaseHelper";

    private static final String TABLE_NAME = "pushup_table";
    private static final String COL1 = "ID";
    private static final String COL2 = "number";


    public DatabaseHelper(Context context) {
        super(context, TABLE_NAME, null, 1);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String createTable = "CREATE TABLE " + TABLE_NAME + " (ID INTEGER PRIMARY KEY AUTOINCREMENT, " +
                COL2 +" TEXT)";
        db.execSQL(createTable);
    }
public String getNumber(int i){
    SQLiteDatabase db = this.getWritableDatabase();
    String query = "SELECT " + COL2 + " FROM " + TABLE_NAME +
            " WHERE " + COL1 + " = '" + i + "'";
    Cursor data = db.rawQuery(query, null);
    //String cursorString = data.getString( data.getColumnIndex(COL1));
    String cursorString = data.getString(0);
    return cursorString;
}}

test

public class test extends AppCompatActivity {
DatabaseHelper mDatabaseHelper;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.test);
        ButterKnife.bind(this);

        mDatabaseHelper = new DatabaseHelper(this);

    }
 @OnClick(R.id.button_data)
    public void data(){

        String numberFromDB = mDatabaseHelper.getNumber(1);

        Toast.makeText(this,"number from db: " + numberFromDB, Toast.LENGTH_SHORT).show();

    }
}

但是它给了我这些错误，而且什么也没发生（当我连接手机时）

E/MemoryLeakMonitorManager: MemoryLeakMonitor.jar is not exist!
E/Minikin: Could not get cmap table size!
E/vndksupport: Could not load vendor/lib64/egl/libGLES_mali_v2.so from sphal namespace: dlopen failed: library "vendor/lib64/egl/libGLES_mali_v2.so" not found.

我当然在数据库中也有一些数据。

当我在模拟器上尝试此操作时，显示了不同的错误：

07-14 19:20:56.702 9681-9681/majer.pompeczki E/AndroidRuntime: FATAL EXCEPTION: main
    Process: majer.pompeczki, PID: 9681
    android.database.CursorIndexOutOfBoundsException: Index -1 requested, with a size of 1
        at android.database.AbstractCursor.checkPosition(AbstractCursor.java:460)
        at android.database.AbstractWindowedCursor.checkPosition(AbstractWindowedCursor.java:136)
        at android.database.AbstractWindowedCursor.getString(AbstractWindowedCursor.java:50)
        at majer.pompeczki.DatabaseHelper.getNumber(DatabaseHelper.java:81)
        at majer.pompeczki.test.trening(test.java:68)
        at majer.pompeczki.test_ViewBinding$3.doClick(test_ViewBinding.java:62)
        at butterknife.internal.DebouncingOnClickListener.onClick(DebouncingOnClickListener.java:22)
        at android.view.View.performClick(View.java:5610)
        at android.view.View$PerformClick.run(View.java:22265)
        at android.os.Handler.handleCallback(Handler.java:751)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:154)
        at android.app.ActivityThread.main(ActivityThread.java:6077)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)