无法使用多个光标从 SQLite 检索数据

【问题标题】：Can't retrieve data from SQLite Using Multiple Cursor无法使用多个光标从 SQLite 检索数据
【发布时间】：2018-10-30 06:28:10
【问题描述】：

我正在尝试使用我创建的 3 种不同的 DatabaseHelper 方法从 2 个表中检索不同的数据 -> “支出”和“交易”表。我必须在我的 Main 类的一个方法中使用所有这 3 个 Cursor 方法，并且我不知道覆盖 Cursor 的正确方法因为我使用了这些数据库方法，例如 myDb.getDeletedCategory、myDb.getLatestAmount 等。所以我认为主要问题是我如何在“deletedcategory”之后定义我的游标，以及在使用游标后“覆盖”或重新定义游标的正确方法是什么：-

Cursor deletedcategory = myDb.getDeletedCategory(transaction_id, position);
                if (deletedcategory.getCount() == 0) {
                    Toast.makeText(AddExpenses.this, "No category found !", Toast.LENGTH_LONG).show();
                } else {
                    deletedcategory.moveToFirst();
                    deletedcategoryis = deletedcategory.getString(0);
                }

Cursor latestamount = myDb.getLatestAmount(position, deletedcategoryis);
                if (latestamount.getCount() == 0) {
                    Toast.makeText(AddExpenses.this, "No amount found in specific category !", Toast.LENGTH_LONG).show();
                } else {
                    latestamount.moveToFirst();
                    amountfromdb_ofcategory = latestamount.getDouble(0);
                }

Cursor deletedamount = myDb.getDeletedAmount(transaction_id, position);
                if (deletedamount.getCount() == 0) {
                    Toast.makeText(AddExpenses.this, "Deleted amount not found !", Toast.LENGTH_LONG).show();
                } else {
                    deletedamount.moveToFirst();
                    amount_deleted = deletedamount.getDouble(0);
                }

【问题讨论】：

  • 尝试关闭游标如 if(!deletedcategory.isClosed()){deletedcategory.close()}，并检查查询是否查询返回数据？
  • 用于删除和更新数据，我们不需要光标对象作为返回
  • 所以你的意思是我需要在整个游标删除类别{}之后和游标最新数量之前添加“if(!deletedcategory.isClosed()){deletedcategory.close()}”？和 "if(!latestamount.isClosed()){latestamount.close()} 在 Cursor latestamount {} 之后和 Cursor deletedamount 之前？
  • 是的，但我认为删除和更新不需要游标，删除可能会将 int 和更新返回为布尔值。
  • delete 应该像 public Integer deletedcategory (Integer id) { SQLiteDatabase db = this.getWritableDatabase(); return db.delete("deletedcategory", "id = ? ", new String[] { Integer.toString(id) }); } ，除非您在删除后不获取数据。

标签： android sqlite android-cursoradapter


【解决方案1】：

您可以直接覆盖现有光标。

例如考虑以下数据库助手（带有 3 个返回游标的方法）：-

public class DBHelper01 extends SQLiteOpenHelper {

    public static final String DBNAME = "db01";
    public static final int DBVERSION = 1;
    public static final String TABLE_SPENDING = "spending";
    public static final String TABLE_TRANSACTIONS = "transactions";
    public static final String SPENDING_COL_ID = BaseColumns._ID;
    public static final String SPENDING_COL_AMOUNT = "amount";
    public static final String SPENDING_COL_CATEGORY = "catetgory";
    public static final String TRANSACTIONS_COL_ID = BaseColumns._ID;
    public static final String TRANSACTIONS_COl_DATE = "date";
    public static final String TRANSACTION_COL_AMOUNT = "amount";
    public static final String TRANSACTION_TYPE = "type";

    public static final int TRANSACTION_TYPE_ADD = 0;
    public static final int TRANSACTION_TYPE_DELETE = 1;
    public static final int TRANSACTION_TYPE_UPDATE = 2;


    String crt_spending_tbl = "CREATE TABLE IF NOT EXISTS " + TABLE_SPENDING + "(" +
            SPENDING_COL_ID + " INTEGER PRIMARY KEY, " +
            SPENDING_COL_AMOUNT + " REAL DEFAULT 0.0," +
            SPENDING_COL_CATEGORY + " TEXT" +
            ")";
    String crt_transactions_tbl = "CREATE TABLE IF NOT EXISTS " + TABLE_TRANSACTIONS + "(" +
            TRANSACTIONS_COL_ID + " INTEGER PRIMARY KEY," +
            TRANSACTIONS_COl_DATE + " TEXT DEFAULT CURRENT_TIMESTAMP," +
            TRANSACTION_COL_AMOUNT + " REAL," +
            TRANSACTION_TYPE + " INTEGER" +
            ")";

    SQLiteDatabase mDB;

    public DBHelper01(Context context) {
        super(context, DBNAME, null, DBVERSION);
        mDB = this.getWritableDatabase();
    }

    @Override
    public synchronized void close() {
        super.close();
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(crt_spending_tbl);
        db.execSQL(crt_transactions_tbl);
    }

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

    }

    public long addSpending(String category, Double amount) {
        ContentValues cv = new ContentValues();
        cv.put(SPENDING_COL_CATEGORY,category);
        cv.put(SPENDING_COL_AMOUNT,amount);
        return mDB.insert(TABLE_SPENDING,null,cv);
    }

    public long addTransactions(Double amount, int transaction_type ) {
        ContentValues cv = new ContentValues();
        cv.put(TRANSACTION_COL_AMOUNT,amount);
        cv.put(TRANSACTION_TYPE,transaction_type);
        return mDB.insert(TABLE_TRANSACTIONS,null,cv);
    }

    public Cursor getLatestTransaction() {
        return mDB.query(TABLE_TRANSACTIONS,null,null,null,null,null,TRANSACTIONS_COl_DATE + " DESC","1");
    }

    public Cursor getTotalTransactionAmount() {
        String[] columns = new String[]{"sum(" + TRANSACTION_COL_AMOUNT + ") AS summed_amounts" };
        return mDB.query(TABLE_TRANSACTIONS,columns,null,null,null,null,null);
    }

    public Cursor getAllTransactions() {
        return mDB.query(TABLE_TRANSACTIONS,null,null,null,null,null,TRANSACTIONS_COl_DATE + " ASC");
    }
}

以及以下调用 3 个方法的 Activity（在最初添加一些数据之后），然后在每次使用后转储光标：-

public class MainActivity extends AppCompatActivity {

    DBHelper01 mDBHlpr;
    Cursor mCsr; //<<<<<<<<<< THE CURSOR THAT WILL BE OVERIDDEN

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

        mDBHlpr = new DBHelper01(this);
        mDBHlpr.addSpending("TEST",123.45);
        mDBHlpr.addTransactions(133.42,DBHelper01.TRANSACTION_TYPE_ADD);
        mDBHlpr.addTransactions(127.45,DBHelper01.TRANSACTION_TYPE_DELETE);
        mDBHlpr.addTransactions(111.11,DBHelper01.TRANSACTION_TYPE_UPDATE);
        mDBHlpr.addTransactions(133.42,DBHelper01.TRANSACTION_TYPE_ADD);
        mDBHlpr.addTransactions(127.45,DBHelper01.TRANSACTION_TYPE_DELETE);
        mDBHlpr.addTransactions(111.11,DBHelper01.TRANSACTION_TYPE_UPDATE);

        mCsr = mDBHlpr.getAllTransactions(); //<<<<<<<<<< First write to cursor
        DatabaseUtils.dumpCursor(mCsr);
        mCsr = mDBHlpr.getLatestTransaction(); //<<<<<<<<<< Overwrites the Cursor
        DatabaseUtils.dumpCursor(mCsr);
        mCsr = mDBHlpr.getTotalTransactionAmount(); // Overwrites the Cursor again
        DatabaseUtils.dumpCursor(mCsr);
        mCsr.close();
    }
}

结果输出（确认每个 Cursor 不同）：-

10-30 11:17:31.937 1252-1252/axtest.axtest I/System.out: >>>>> Dumping cursor android.database.sqlite.SQLiteCursor@5345bd2c
10-30 11:17:31.937 1252-1252/axtest.axtest I/System.out: 0 {
10-30 11:17:31.937 1252-1252/axtest.axtest I/System.out:    _id=1
10-30 11:17:31.937 1252-1252/axtest.axtest I/System.out:    date=2018-10-30 11:17:31
10-30 11:17:31.937 1252-1252/axtest.axtest I/System.out:    amount=133.42
10-30 11:17:31.937 1252-1252/axtest.axtest I/System.out:    type=0
10-30 11:17:31.937 1252-1252/axtest.axtest I/System.out: }
10-30 11:17:31.937 1252-1252/axtest.axtest I/System.out: 1 {
10-30 11:17:31.937 1252-1252/axtest.axtest I/System.out:    _id=2
10-30 11:17:31.937 1252-1252/axtest.axtest I/System.out:    date=2018-10-30 11:17:31
10-30 11:17:31.937 1252-1252/axtest.axtest I/System.out:    amount=127.45
10-30 11:17:31.937 1252-1252/axtest.axtest I/System.out:    type=1
10-30 11:17:31.937 1252-1252/axtest.axtest I/System.out: }
10-30 11:17:31.937 1252-1252/axtest.axtest I/System.out: 2 {
10-30 11:17:31.937 1252-1252/axtest.axtest I/System.out:    _id=3
10-30 11:17:31.937 1252-1252/axtest.axtest I/System.out:    date=2018-10-30 11:17:31
10-30 11:17:31.937 1252-1252/axtest.axtest I/System.out:    amount=111.11
10-30 11:17:31.937 1252-1252/axtest.axtest I/System.out:    type=2
10-30 11:17:31.937 1252-1252/axtest.axtest I/System.out: }
10-30 11:17:31.937 1252-1252/axtest.axtest I/System.out: 3 {
10-30 11:17:31.937 1252-1252/axtest.axtest I/System.out:    _id=4
10-30 11:17:31.937 1252-1252/axtest.axtest I/System.out:    date=2018-10-30 11:17:31
10-30 11:17:31.937 1252-1252/axtest.axtest I/System.out:    amount=133.42
10-30 11:17:31.937 1252-1252/axtest.axtest I/System.out:    type=0
10-30 11:17:31.937 1252-1252/axtest.axtest I/System.out: }
10-30 11:17:31.941 1252-1252/axtest.axtest I/System.out: 4 {
10-30 11:17:31.941 1252-1252/axtest.axtest I/System.out:    _id=5
10-30 11:17:31.941 1252-1252/axtest.axtest I/System.out:    date=2018-10-30 11:17:31
10-30 11:17:31.941 1252-1252/axtest.axtest I/System.out:    amount=127.45
10-30 11:17:31.941 1252-1252/axtest.axtest I/System.out:    type=1
10-30 11:17:31.941 1252-1252/axtest.axtest I/System.out: }
10-30 11:17:31.941 1252-1252/axtest.axtest I/System.out: 5 {
10-30 11:17:31.941 1252-1252/axtest.axtest I/System.out:    _id=6
10-30 11:17:31.941 1252-1252/axtest.axtest I/System.out:    date=2018-10-30 11:17:31
10-30 11:17:31.941 1252-1252/axtest.axtest I/System.out:    amount=111.11
10-30 11:17:31.941 1252-1252/axtest.axtest I/System.out:    type=2
10-30 11:17:31.941 1252-1252/axtest.axtest I/System.out: }
10-30 11:17:31.941 1252-1252/axtest.axtest I/System.out: <<<<<



10-30 11:17:31.941 1252-1252/axtest.axtest I/System.out: >>>>> Dumping cursor android.database.sqlite.SQLiteCursor@5342f0e4
10-30 11:17:31.941 1252-1252/axtest.axtest I/System.out: 0 {
10-30 11:17:31.941 1252-1252/axtest.axtest I/System.out:    _id=1
10-30 11:17:31.941 1252-1252/axtest.axtest I/System.out:    date=2018-10-30 11:17:31
10-30 11:17:31.941 1252-1252/axtest.axtest I/System.out:    amount=133.42
10-30 11:17:31.941 1252-1252/axtest.axtest I/System.out:    type=0
10-30 11:17:31.941 1252-1252/axtest.axtest I/System.out: }
10-30 11:17:31.941 1252-1252/axtest.axtest I/System.out: <<<<<



10-30 11:17:31.941 1252-1252/axtest.axtest I/System.out: >>>>> Dumping cursor android.database.sqlite.SQLiteCursor@5342f6e8
10-30 11:17:31.941 1252-1252/axtest.axtest I/System.out: 0 {
10-30 11:17:31.941 1252-1252/axtest.axtest I/System.out:    summed_amounts=743.96
10-30 11:17:31.941 1252-1252/axtest.axtest I/System.out: }
10-30 11:17:31.941 1252-1252/axtest.axtest I/System.out: <<<<<

【讨论】：

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