如何从RecyclerView和数据库中删除项目？

Question

从RecyclerView添加和删除项目是可行的，但是我不知道我是否在数据库中编写了删除行的好方法，因为只有我在添加项目和删除项目以及是否从应用程序离开时正在保存条件，并且回来，但以前我已经删除了一些项目，我在那里看到它们。 因此，我需要有关数据库中此方法的一些帮助，以删除项目并在活动中实施它。

这是我的代码：

数据库：

    public class DBHelper extends SQLiteOpenHelper  {
    private static final String DATABASE_NAME = "items.db";
    private static final int DATABASE_VERSION = 1;

    private final String TABLE_ITEMS = "items";

    private final String COLUMN_ID = "id";
    private final String COLUMN_ITEM = "item";

    private static DBHelper dbh;

    private DBHelper(Activity activity) {
        super(activity, DATABASE_NAME, null, DATABASE_VERSION);
    }

    public static synchronized DBHelper getConnection(Activity activity) {
        if (dbh == null)
            dbh = new DBHelper(activity);
        return dbh;
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String upitZaPravljanjeBaze =
                "CREATE TABLE "+TABLE_ITEMS+"("+COLUMN_ID+" INTEGER PRIMARY KEY, "+COLUMN_ITEM+" TEXT);";
        db.execSQL(upitZaPravljanjeBaze);

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        if (newVersion > oldVersion) {
            db.execSQL("DROP TABLE" + "TABLE_ITEMS");
            onCreate(db);
        }

    }

    public ArrayList<String> getAllItems() {
        ArrayList<String> toRet = new ArrayList<String>();
        SQLiteDatabase db = getReadableDatabase();
        Cursor c = db.rawQuery("SELECT * FROM " + TABLE_ITEMS, null);
        c.moveToFirst();

        while(c.isAfterLast() == false) {
            toRet.add(c.getString(c.getColumnIndex(COLUMN_ITEM)));
            c.moveToNext();

        }

        return toRet;
    }

    public long saveItem(String item) {
        SQLiteDatabase db = getWritableDatabase();
        ContentValues cv = new ContentValues();
        cv.put(COLUMN_ITEM, item);
        return db.insert(TABLE_ITEMS, null, cv);
    }

    public boolean deleteItem(long rowId) {
        SQLiteDatabase db = getReadableDatabase();
        return db.delete(TABLE_ITEMS, COLUMN_ID + "=" + rowId, null) > 0;
    }

}

适配器：

    public class AdapterRecyclerAnimators extends RecyclerView.Adapter<AdapterRecyclerAnimators.Holder> {
    private ArrayList<String> mListData = new ArrayList<>();
    private LayoutInflater mLayoutInflater;


    public AdapterRecyclerAnimators(Context context) {
        mLayoutInflater = LayoutInflater.from(context);
    }


    @Override
    public Holder onCreateViewHolder(ViewGroup parent, int viewType) {
        View row = mLayoutInflater.inflate(R.layout.custom_row_item, parent, false);
        Holder holder = new Holder(row);
        return holder;
    }

    @Override
    public void onBindViewHolder(Holder holder, final int position) {
        String data = mListData.get(position);
        holder.textDataItem.setText(data);
        holder.buttonDelete.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                removeItem(position);
            }
        });
    }

    public void addItem(String item) {
        mListData.add(item);
        notifyItemInserted(mListData.size());
    }
    public void addAll(ArrayList<String> newList){
        mListData = newList;
        notifyDataSetChanged();
    }

    public void removeItem(String item) {
        int position = mListData.indexOf(item);
        if (position != -1) {
            mListData.remove(item);
            notifyItemRemoved(position);
        }
    }

    public void removeItem(int position) {
        mListData.remove(position);
        notifyItemRemoved(position);
    }

    @Override
    public int getItemCount() {
        return mListData.size();
    }

    public static class Holder extends RecyclerView.ViewHolder {
        TextView textDataItem;
        ImageButton buttonDelete;

        public Holder(View itemView) {
            super(itemView);
            textDataItem = (TextView) itemView.findViewById(R.id.text_item);
            buttonDelete = (ImageButton) itemView.findViewById(R.id.button_delete);

        }
    }

}

主要活动：

    public class MainActivity extends BaseActivity {

    //int containing the duration of the animation run when items are added or removed from the RecyclerView
    public static final int ANIMATION_DURATION = 2000;
    //edit text letting the user type item name to be added to the recylcerview
    private EditText mInput;
    //itemcounter for recyclerview
    private TextView mItemCounter;
    //recyclerview showing all items added by the user
    private RecyclerView mRecyclerView;
    private AdapterRecyclerAnimators mAdapter;
    ArrayList<String> mListData = new ArrayList<>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        initViews();

        if(savedInstanceState != null){
            ArrayList<String> items = savedInstanceState.getStringArrayList("items");
            mListData.addAll(items);
            mAdapter.notifyDataSetChanged();
        }

    }

    @Override
    public void onSaveInstanceState(Bundle outState) {
        outState.putStringArrayList("items", mListData);
    }

    private void initViews(){
        mInput = (EditText) findViewById(R.id.text_input);
        mRecyclerView = (RecyclerView) findViewById(R.id.recyclerAnimatedItems);
        mItemCounter = (TextView) findViewById(R.id.itemCounter);
        mItemCounter.setText(String.valueOf(mRecyclerView.getChildCount()));
        mAdapter = new AdapterRecyclerAnimators(this);
        //set an animator on the RecyclerView that works only when items are added or removed
        mRecyclerView.setItemAnimator(new SlideInLeftAnimator());
        mRecyclerView.getItemAnimator().setAddDuration(ANIMATION_DURATION);
        mRecyclerView.getItemAnimator().setRemoveDuration(ANIMATION_DURATION);
        mAdapter.addAll(DBHelper.getConnection(MainActivity.this).getAllItems());
        mRecyclerView.setAdapter(mAdapter);
        mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
    }

    public void addItem(View view) {
        //check if the EditText has valid contents
        if (Util.hasValidContents(mInput)) {
            DBHelper.getConnection(MainActivity.this)
                    .saveItem(mInput.getText().toString());

            ArrayList<String> allItems = DBHelper.getConnection(MainActivity.this).getAllItems();

            mAdapter.addAll(allItems);

            mInput.setText("");
        }
    }

    @Override
    protected int getLayoutResourceId() {
        return R.layout.activity_main;
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

Answer 1

这些是您的删除方法：

public void removeItem(String item) {
    int position = mListData.indexOf(item);
    if (position != -1) {
        mListData.remove(item);
        notifyItemRemoved(position);
    }
}

public void removeItem(int position) {
    mListData.remove(position);
    notifyItemRemoved(position);
}

您从列表中删除了项目，但从未将其从数据库中删除。 在这两种方法中都调用您的delete方法，并查看其是否有效。

Answer 2

不一定认为这可以解决您的问题，但我想指出，在您的数据库删除方法中，您可以：

SQLiteDatabase db = getReadableDatabase();

您可能要切换：

SQLiteDatabase db = getWritableDatabase();