删除listView和数据库中的项目

Question

我在listView中单击项目后，同时尝试删除listView和数据库中的对象。我想在删除项目之前打开一个警告对话框。我已经阅读了许多关于此的堆栈溢出问题，例如：

how can i delete an item from listview and also database

delete a specific item from listview stored in database in android application

Delete item from database - ListView - Android

还有很多人......我发现他们都没有帮助。有什么建议吗？

Main_Activity：

public class New_Recipe extends AppCompatActivity {

Button add, done;
EditText Recipe_Name, Recipe_Item, Recipe_Steps;
String search;
WebView webView;
DatabaseHelper databaseHelper;
ListView ItemsList;
Context context = this;
SQLiteDatabase sqLiteDatabase;
Cursor cursor;
RecipeListAdapter listAdapter;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_new__recipe);
    setTitle("New Recipe");
    add = (Button) findViewById(R.id.button2);
    done = (Button) findViewById(R.id.button);
    Recipe_Name = (EditText) findViewById(R.id.editText);
    Recipe_Item = (EditText) findViewById(R.id.editText2);
    Recipe_Steps = (EditText) findViewById(R.id.editText3);
    webView = (WebView) findViewById(R.id.webView);
    ItemsList = (ListView) findViewById(R.id.listView);
    listAdapter = new RecipeListAdapter(getApplicationContext(), R.layout.recipe_textview);
    context = this;
    AddData();



}
//When the add button is pressed
public void AddData() {
  add.setOnClickListener(new View.OnClickListener() {
      @Override
      public void onClick(View v) {
          String item = Recipe_Item.getText().toString();

          databaseHelper = new DatabaseHelper(context);
          sqLiteDatabase = databaseHelper.getWritableDatabase();

          databaseHelper.addItems(item, sqLiteDatabase);

          Toast.makeText(getBaseContext(), "Item inserted", Toast.LENGTH_LONG).show();

          databaseHelper.close();

          ItemsList.setAdapter(listAdapter);

          databaseHelper = new DatabaseHelper(getApplicationContext());
          sqLiteDatabase = databaseHelper.getReadableDatabase();

          cursor = databaseHelper.getItems(sqLiteDatabase);

          if (cursor.moveToFirst()) {
              do {

                  String items;

                  items = cursor.getString(0);

                  RecipeDataProvider dataProvider = new RecipeDataProvider(items);

                  listAdapter.add(dataProvider);

              } while (cursor.moveToNext());
          }
      }

  });

}







public void onSearch(View v) {
    search = "Recipes";
    webView.loadUrl("https://www.google.com/search?q=" + search);

}

@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_new__recipe, 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);
}

DatabaseHelper类：

public class DatabaseHelper extends SQLiteOpenHelper {
public static final int DATABASE_VERSION = 5;
public static final String DATABASE_NAME = "Recipes.db";
public static final String CREATE_QUERRY = "create table " + RecipeContract.RecipeEntry.TABLE_NAME + "( _ID INTEGER PRIMARY KEY, NAME text, ITEMS text, STEPS text)";


public DatabaseHelper(Context context) {
    super(context, DATABASE_NAME, null, DATABASE_VERSION);
    Log.d("Recipe Database", "Database should be made!");
}


@Override
public void onCreate(SQLiteDatabase db) {
    db.execSQL(CREATE_QUERRY);
    Log.d("Recipe Database", "Table should be made!");
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

}

public void addItems(String items, SQLiteDatabase db)
{
    ContentValues values = new ContentValues();

    values.put(RecipeContract.RecipeEntry.COL2,items);

    db.insert(RecipeContract.RecipeEntry.TABLE_NAME,null,values);

    Log.e("Recipe Database","Item should be added to the table!");

}
public Cursor getItems(SQLiteDatabase db)
{
    Cursor cursor;
    String[] projections = {RecipeContract.RecipeEntry.COL2};

cursor = db.query(RecipeContract.RecipeEntry.TABLE_NAME,projections,null,null,null,null,null);

    return cursor;
}

ListViewAdapter：

public class RecipeListAdapter extends ArrayAdapter {

List list = new ArrayList();

public RecipeListAdapter(Context context, int resource) {
    super(context, resource);
}

static class LayoutHandler
{
    TextView ITEM;
}


@Override
public void add(Object object) {
    super.add(object);
    list.add(object);
}

@Override
public int getCount() {
    return super.getCount();
}

@Override
public Object getItem(int position) {
    return super.getItem(position);
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {

    View row = convertView;

    LayoutHandler layoutHandler;


    if (row == null)
    {

        LayoutInflater layoutInflater = (LayoutInflater) this.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        row = layoutInflater.inflate(R.layout.recipe_textview,parent,false);

        layoutHandler = new LayoutHandler();

        layoutHandler.ITEM = (TextView) row.findViewById(R.id.tx_items);

        row.setTag(layoutHandler);

    } else {

        layoutHandler = (LayoutHandler) row.getTag();
    }

    RecipeDataProvider dataProvider = (RecipeDataProvider) this.getItem(position);
    layoutHandler.ITEM.setText(dataProvider.getItems().toString());

    return row;
}

编辑：我更新的Main_Activity类

public class New_Recipe extends AppCompatActivity {

Button add, done;
EditText Recipe_Name, Recipe_Item, Recipe_Steps;
String search;
WebView webView;
DatabaseHelper databaseHelper;
ListView ItemsList;
Context context = this;
SQLiteDatabase sqLiteDatabase;
Cursor cursor;
RecipeListAdapter listAdapter;
List<New_Recipe> list = new ArrayList<>();
private int id;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_new__recipe);
    setTitle("New Recipe");
    add = (Button) findViewById(R.id.button2);
    done = (Button) findViewById(R.id.button);
    Recipe_Name = (EditText) findViewById(R.id.editText);
    Recipe_Item = (EditText) findViewById(R.id.editText2);
    Recipe_Steps = (EditText) findViewById(R.id.editText3);
    webView = (WebView) findViewById(R.id.webView);
    ItemsList = (ListView) findViewById(R.id.listView);
    listAdapter = new RecipeListAdapter(getApplicationContext(), R.layout.recipe_textview);
    context = this;

    AddData();


    ItemsList.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
        @Override
        public boolean onItemLongClick(AdapterView<?> parent, View view, int position, long id) {
            Object getSelectedItem = list.get(position);

            databaseHelper.deleteItem(getSelectedItem);
            listAdapter.deleteitem(getSelectedItem);

            return true;
        }
    });



}

public New_Recipe(){

}

public int getId() {
    return id;
}

public void setId(int id) {
    this.id = id;
}

Answer 1

您可以使用此方法从DatabaseHelper类中删除行：

public void deleteItem(Object item) {
    SQLiteDatabase db = this.getWritableDatabase();
    db.delete(TABLE_NAME, KEY_ID + " = ?",
            new String[]{String.valueOf(item.getId())});
    db.close();
}

然后你还需要一个从适配器中删除对象的方法：

public void deleteItem(Object item) {
    listArray.remove(item);
    notifyDataSetChanged();
}

现在你可以在这样的活动中调用所有这个方法：

让我们假设您要通过单击列表项上的长按来删除所有这些：

listView.setOnItemLongClickListener(new OnItemLongClickListener() {
        @Override
        public boolean onItemLongClick(AdapterView<?> arg0, View arg1,
                int pos, long id) {
            Object getSelectedItem = arrayList.get(pos);

            dataBaseHelper.deleteItem(getSelectedItem);
            adapter.deleteItem(getSelectedItem);

            return true;
        }
    }); 

<强>更新：

在尝试调用方法getId()之前，您需要在类中创建该方法。所以你需要在你的类中创建get和setter方法，如下所示：

一步一步：

1. 将您的班级New_Recipe更改为MainActivity。如果您收到错误，只需突出显示该错误，您将看到＆＃34;重命名文件＆＃34;。

   1. 在主要课程之外创建一个新课程，并将其命名为NewRecipe：

      public class NewRecipe {

      private int id;

      private String title;

      public NewRecipe() {  // empty constructor  }

      public int getId() { return id; }

      public void setId(int id) { this.id = id; } }

现在你可以做我之前解释的所有事情。

Answer 2

您需要DatabaseHelper类中的函数delete

public boolean delete(long rowId) {
      return db.delete(TABLE_NAME, KEY_ROWID + "=" + rowId, null) > 0;
    }

您需要在活动deleteItem（）中使用与addItems()

类似的功能

public void deleteItem(){

//Based on some logic,find the rowID of the table which needs to be deleted and call delete function of DatabaseHelper class.
}

在ListViewAdapter中，您需要定义一个方法delete

public void delete(Object object) {
    list.remove(object);
    //To update the ListView in Android
    this.notifyDataSetChanged();
}