如何将单个 SQLite 数据显示到 textview 中？

Question

I want to retrieve amount from an existing database and display it in a TextView.

I've created database. But when I'm trying to fetch and display the amount, my app keeps crash.

/ DataBaseHelper.java /

   public Cursor getBalance(String amount) {
    SQLiteDatabase db = this.getReadableDatabase();

    String selectQuery = "SELECT  * FROM " + TABLE_USER_BALANCE + " WHERE "
            + KEY_AMOUTNT + " = " + amount;

    Log.e(LOG, selectQuery);

    Cursor c = db.rawQuery(selectQuery, null);

    if (c != null)
        c.moveToFirst();

    Balance b = new Balance();
    b.setAmount(c.getInt(c.getColumnIndex(KEY_AMOUTNT)));

    return (Cursor) b;
}

Dashboard class:

public void saveCallBack(Balance balance) {


   DataBaseHelper dataBaseHelper = new DataBaseHelper(context);
    Cursor cursor = dataBaseHelper.getBalance(DashBoard.email);
  while (cursor.moveToNext()) {
        String s_amount = "";
        s_amount = 
      cursor.getString(cursor.getColumnIndex(DataBaseHelper.KEY_AMOUTNT));

        Double amount = 0.0;
        if (AppUtility.isNum(s_amount)) {
            amount = Double.parseDouble(s_amount);
        }

        TextView Amount = findViewById(R.id.amount);
        Amount.setText(String.valueOf(amount));


    }

}

Answer 1

You are casting a Balance to a Cursor which is not possible, and therefore your app will crash. You either want to return the database Cursor itself or the Balance object. You already made the Balance instance and placed some value in it, so I assume your code should be this:

public Balance getBalance(String amount) {
    ...

    Balance b = new Balance();
    b.setAmount(c.getInt(c.getColumnIndex(KEY_AMOUTNT)));
    return b;
}

I would suggest you learn a bit more about casting in Java, so you will understand the casting behavior.