Question

我有ListView SQL DataBase。可以使用两个EditText动态添加它的值。

我想知道如何删除SQL DataBase中的行。现在我可以通过rowId删除一行，因此将删除包含所有值的整行。但我希望只删除该行，以便有连续的数字。

例如ListView。

1 Text1
2 Text2
3 Text3
4 Text4

如果我要删除第3行，我的代码就是这样：

1 Text1
2 Text2
4 Text4

但是我想要删除第3行时的样子：

1 Text1
2 Text2
3 Text4

我的代码：

MainActivity

private void listViewItemLongClick() {
        ListView myList = (ListView) findViewById(R.id.list);
        myList.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
            @Override
            public boolean onItemLongClick(AdapterView<?> parent, View viewClicked, final int position, final long id) {

                AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);
                        //Set header
                        builder.setTitle("delete");
                        builder.setMessage("Are you sure ? ");
                                //set the OK button with an onClickListener
                        builder.setPositiveButton("yes", new DialogInterface.OnClickListener() {
                            //edit the userinput
                            public void onClick(DialogInterface dialog, int whichButton) {
                                myDb.deleteRow(id);
                                populateListView();
                            }
                        }).setNegativeButton("no", new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int whichButton) {
                        // Do nothing.
                    }
                }).show();

                return false;
            }
        });
    }

将对DBAdapter

public class DBAdapter {

    private static final String TAG = "DBAdapter"; //used for logging database version changes

    // Field Names:
    public static final String KEY_ROWID = "_id";
    public static final String KEY_WDH = "task";
    public static final String KEY_KG = "date";

    public static final String[] ALL_KEYS = new String[]{KEY_ROWID, KEY_WDH, KEY_KG};

    public static final String DATABASE_NAME = "dbToDo";
    public static final String DATABASE_TABLE = "mainToDo";
    public static final int DATABASE_VERSION = 2; // The version number must be incremented each time a change to DB structure occurs.

    //SQL statement to create database
    private static final String DATABASE_CREATE_SQL =
            "CREATE TABLE " + DATABASE_TABLE
                    + " (" + KEY_ROWID + " INTEGER PRIMARY KEY AUTOINCREMENT, "
                    + KEY_WDH + " TEXT NOT NULL, "
                    + KEY_KG + " TEXT"
                    + ");";

    private final Context context;
    private DatabaseHelper myDBHelper;
    private SQLiteDatabase db;


    public DBAdapter(Context ctx) {
        this.context = ctx;
        myDBHelper = new DatabaseHelper(context);
    }

    // Open the database connection.
    public DBAdapter open() {
        db = myDBHelper.getWritableDatabase();
        return this;
    }

    // Close the database connection.
    public void close() {
        myDBHelper.close();
    }

    // Add a new set of values to be inserted into the database.
    public long insertRow(String task, String date) {
        ContentValues initialValues = new ContentValues();
        initialValues.put(KEY_WDH, task);
        initialValues.put(KEY_KG, date);

        // Insert the data into the database.
        return db.insert(DATABASE_TABLE, null, initialValues);
    }

    // Delete a row from the database, by rowId (primary key)
    public boolean deleteRow(long rowId) {
        String where = KEY_ROWID + "=" + rowId;
        return db.delete(DATABASE_TABLE, where, null) != 0;
    }

    // Return all data in the database.
    public Cursor getAllRows() {
        String where = null;
        Cursor c = db.query(true, DATABASE_TABLE, ALL_KEYS, where, null, null, null, null, null);
        if (c != null) {
            c.moveToFirst();
        }
        return c;
    }

    // Get a specific row (by rowId)
    public Cursor getRow(long rowId) {
        String where = KEY_ROWID + "=" + rowId;
        Cursor c = db.query(true, DATABASE_TABLE, ALL_KEYS,
                where, null, null, null, null, null);
        if (c != null) {
            c.moveToFirst();
        }
        return c;
    }

    // Change an existing row to be equal to new data.
    public boolean updateRow(long rowId, String task, String date) {
        String where = KEY_ROWID + "=" + rowId;
        ContentValues newValues = new ContentValues();
        newValues.put(KEY_WDH, task);
        newValues.put(KEY_KG, date);
        // Insert it into the database.
        return db.update(DATABASE_TABLE, newValues, where, null) != 0;
    }


    private static class DatabaseHelper extends SQLiteOpenHelper {
        DatabaseHelper(Context context) {
            super(context, DATABASE_NAME, null, DATABASE_VERSION);
        }

        @Override
        public void onCreate(SQLiteDatabase _db) {
            _db.execSQL(DATABASE_CREATE_SQL);
        }

        @Override
        public void onUpgrade(SQLiteDatabase _db, int oldVersion, int newVersion) {
            Log.w(TAG, "Upgrading application's database from version " + oldVersion
                    + " to " + newVersion + ", which will destroy all old data!");

            // Destroy old database:
            _db.execSQL("DROP TABLE IF EXISTS " + DATABASE_TABLE);

            // Recreate new database:
            onCreate(_db);
        }
    }


}

Answer 1

它很乱，因为它看起来像是你的标识栏，而你正试图消除这些空白。这不是一种好的做法，但有一种机制可以做到这一点。从概念上讲，这将是一个4步骤的过程。

创建一个具有相同结构的新临时表（包括自动递增标识字段）。
将主表中的剩余行推入临时表。我本来要写这个，但是这样做的伪代码已经存在了。例如，here's an answer to a similar question有一个好的（包括一个免责声明，我说这是一个坏主意）。
放下原来的桌子。
将临时表重命名为原始表的名称。

请注意，每次执行删除操作时都要重写整个表，因此此解决方案无法很好地扩展。

更好的方法是在表中添加一个非标识整数字段，用于存储始终连续的整数值。保持这个领域是你的责任。例如......

在数据的初始填充时，将此字段设置为等于标识字段。

在“删除行”例程中

// Delete a row from the database, by rowId (primary key)
public boolean deleteRow(long rowId) {
    String where = KEY_ROWID + "=" + rowId;
    boolean myReturnValue;
    myReturnValue = db.delete(DATABASE_TABLE, where, null) != 0;
    db.execSQL("UPDATE " + DATABASE_TABLE + " SET MyNewNonIdentitySequentialIntegerField = MyNewNonIdentitySequentialIntegerField -1) WHERE KEY_ROWID > " + String.valueOf(rowId) + ";") ;
    return myReturnValue;
}

插入或插入新记录后，您需要通过将其设置为MAX（MyNewNonIdentitySequentialIntegerField）+ 1来填充它。

如何删除SQL DataBase上的行

1 个答案: