java - 通过数据库从另一个 Activity 的 ListView 中删除项目

Question

嗨，我想从我之前从另一个 Activity 保存的第二个 Activity 的 ListView 中删除(删除)一个项目。我发现了关于从数据库中删除行的类似问题，但我认为我的数据库中有一些变化，并且其他问题和答案中给出了一些变化。这是我的代码。

我保存和删除行的 Activity 。这里我想从 ListView 中删除该行。

   case R.id.id_favorit:
// Add it to the DB and re-draw the ListView
                myDb.insertRow("Atherosclerosis", 0, "");
                Toast.makeText(getApplicationContext(), "Item Added to favorite list!", Toast.LENGTH_SHORT).show(); 
                favClicked=true;
                editor.putBoolean("menu_item", favClicked);
                editor.commit();
                invalidateOptionsMenu();
                return true;

            case R.id.id_favorit2:
                myDb.deleteRow(??);
                Toast.makeText(getApplicationContext(), "Item deleted from favorite list!", Toast.LENGTH_SHORT).show(); 
                favClicked=false;
                editor.putBoolean("menu_item", favClicked);
                editor.commit();
                invalidateOptionsMenu();
                return super.onOptionsItemSelected(item); 
            }
        return true;
        }

这是我的数据库

public class DBAdapter {

    /////////////////////////////////////////////////////////////////////
    //  Constants & Data
    /////////////////////////////////////////////////////////////////////
    // For logging:
    private static final String TAG = "DBAdapter";

    // DB Fields
    public static final String KEY_ROWID = "_id";
    public static final int COL_ROWID = 0;
    /*
     * CHANGE 1:
     */
    // TODO: Setup your fields here:
    public static final String KEY_NAME = "name";
    public static final String KEY_STUDENTNUM = "studentnum";
    public static final String KEY_FAVCOLOUR = "favcolour";

    // TODO: Setup your field numbers here (0 = KEY_ROWID, 1=...)
    public static final int COL_NAME = 1;
    public static final int COL_STUDENTNUM = 2;
    public static final int COL_FAVCOLOUR = 3;


    public static final String[] ALL_KEYS = new String[] {KEY_ROWID, KEY_NAME, KEY_STUDENTNUM, KEY_FAVCOLOUR};

    // DB info: it's name, and the table we are using (just one).
    public static final String DATABASE_NAME = "MyDb";
    public static final String DATABASE_TABLE = "mainTable";
    // Track DB version if a new version of your app changes the format.
    public static final int DATABASE_VERSION = 2;   

    private static final String DATABASE_CREATE_SQL = 
            "create table " + DATABASE_TABLE 
            + " (" + KEY_ROWID + " integer primary key autoincrement, "

            /*
             * CHANGE 2:
             */
            // TODO: Place your fields here!
            // + KEY_{...} + " {type} not null"
            //  - Key is the column name you created above.
            //  - {type} is one of: text, integer, real, blob
            //      (http://www.sqlite.org/datatype3.html)
            //  - "not null" means it is a required field (must be given a value).
            // NOTE: All must be comma separated (end of line!) Last one must have NO comma!!
            + KEY_NAME + " text not null, "
            + KEY_STUDENTNUM + " integer not null, "
            + KEY_FAVCOLOUR + " string not null"

            // Rest  of creation:
            + ");";

    // Context of application who uses us.
    private final Context context;

    private DatabaseHelper myDBHelper;
    private SQLiteDatabase db;

    /////////////////////////////////////////////////////////////////////
    //  Public methods:
    /////////////////////////////////////////////////////////////////////

    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 the database.
    @SuppressLint("NewApi")
    public long insertRow(String name, int studentNum, String favColour) {

    Cursor c= db.query(true, DATABASE_TABLE, ALL_KEYS, KEY_NAME + "='" + name +"'", null, null, null, null, null, null);

    if(c.getCount()>0){
        return -1;
    }
    c.close();
        /*
         * CHANGE 3:
         */     
        // TODO: Update data in the row with new fields.
        // TODO: Also change the function's arguments to be what you need!
        // Create row's data:
        ContentValues initialValues = new ContentValues();
        initialValues.put(KEY_NAME, name);
        initialValues.put(KEY_STUDENTNUM, studentNum);
        initialValues.put(KEY_FAVCOLOUR, favColour);

        // Insert it 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;
    }

    public void deleteAll() {
        Cursor c = getAllRows();
        long rowId = c.getColumnIndexOrThrow(KEY_ROWID);
        if (c.moveToFirst()) {
            do {
                deleteRow(c.getLong((int) rowId));              
            } while (c.moveToNext());
        }
        c.close();
    }

    // Return all data in the database.
    @SuppressLint("NewApi")
    public Cursor getAllRows() {
        String where = null;
        Cursor c =  db.query(true, DATABASE_TABLE, ALL_KEYS, 
                            where, null, null, null, KEY_ROWID + " DESC", 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 name, int studentNum, String favColour) {
        String where = KEY_ROWID + "=" + rowId;

        /*
         * CHANGE 4:
         */
        // TODO: Update data in the row with new fields.
        // TODO: Also change the function's arguments to be what you need!
        // Create row's data:
        ContentValues newValues = new ContentValues();
        newValues.put(KEY_NAME, name);
        newValues.put(KEY_STUDENTNUM, studentNum);
        newValues.put(KEY_FAVCOLOUR, favColour);

        // Insert it into the database.
        return db.update(DATABASE_TABLE, newValues, where, null) != 0;
    }



    /////////////////////////////////////////////////////////////////////
    //  Private Helper Classes:
    /////////////////////////////////////////////////////////////////////

    /**
     * Private class which handles database creation and upgrading.
     * Used to handle low-level database access.
     */
    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);
        }
    }
}

现在我的 ListView 另一个 Activity

private void populateListViewFromDB() {
        Cursor cursor = myDb.getAllRows();

        // Allow activity to manage lifetime of the cursor.
        // DEPRECATED! Runs on the UI thread, OK for small/short queries.
        startManagingCursor(cursor);

        // Setup mapping from cursor to view fields:
        String[] fromFieldNames = new String[] 
                {DBAdapter.KEY_NAME, DBAdapter.KEY_STUDENTNUM};
        int[] toViewIDs = new int[]
                {R.id.item_name};

        // Create adapter to may columns of the DB onto elemesnt in the UI.
        SimpleCursorAdapter myCursorAdapter = 
                new SimpleCursorAdapter(
                        this,       // Context
                        R.layout.item_layout,   // Row layout template
                        cursor,                 // cursor (set of DB records to map)
                        fromFieldNames,         // DB Column names
                        toViewIDs               // View IDs to put information in
                        );

        // Set the adapter for the list view
        ListView myList = (ListView) findViewById(R.id.favlistView1);
        myList.setAdapter(myCursorAdapter);
    }

    private void registerListClickCallback() {
        ListView myList = (ListView) findViewById(R.id.favlistView1);



        //This code is for to delete the single item from the listview of favorite list
        myList.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {

            @Override
            public boolean onItemLongClick(AdapterView<?> arg0, View arg1,
                    int arg2, final long arg3) {
                Cursor cursor = myDb.getRow(arg3);
                if (cursor.moveToFirst()) {


                        new AlertDialog.Builder(FavoriteDiseases.this)
                        .setTitle("Delete Item")
                        .setMessage("Do you want to delete this disease?")
                        .setPositiveButton(android.R.string.yes, new DialogInterface.OnClickListener() {
                       public void onClick(DialogInterface dialog, int which) { 
                                // continue with delete
                                myDb.deleteRow(arg3);
                                populateListViewFromDB();
                        }
                     })
                    .setNegativeButton(android.R.string.no, new DialogInterface.OnClickListener() {
                        public void onClick(DialogInterface dialog, int which) { 
                            // do nothing
                        }
                     })
                     .show();            
    }
                return true;

            }

        });

Answer 1

如果您使用LoaderManager和CursorLoader从数据库加载数据，它将更新光标，并且您可以更新您的ListView当数据库更改时自动。这是一个链接:Loaders