I'm making a project in Android/Java. I have an activity with a listview that displays values from a database and a remove button. For the moment, each row of this list view consists of a checktextview. This last one displays the name of an element of the database. I want to select different elements (with the check text view) and then if I press the remove button, all the selected elements have to be removed from the list and from database. In the following I put the essential parts of my classes. I already done most of the work. This is my activity:
public class ShoppingListActivity extends AppCompatActivity {
// Variables for the management of the database
private DBManagerShoppingList dbShoppingList;
private Cursor crs;
// List view for the shopping list elements
private ListView shoppingListListView;
private ShoppingListViewAdapter shoppingListViewAdapter;
// Generic variables
private String selectedShoppingList;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_shopping_list);
// Find of the useful widgets
shoppingListListView = findViewById(R.id.listViewSelShoppingList);
shoppingListsSpinner = findViewById(R.id.spinnerShoppingLists);
selectedShoppingList = "List_1";
populateListView();
}
// Populate list view from database
public void populateListView() {
// Database management
dbShoppingList = new DBManagerShoppingList(this, selectedShoppingList);
crs = dbShoppingList.query();
new Handler().post(new Runnable() {
@Override
public void run() {
shoppingListViewAdapter = new ShoppingListViewAdapter(ShoppingListActivity.this, crs, 0);
shoppingListListView.setAdapter(shoppingListViewAdapter);
}
});
}
// Remove selected elements
public void removeSelectedElements(View btnRemove) {
// TODO
}
}
This is my custom adapter:
public class ShoppingListViewAdapter extends CursorAdapter {
private LayoutInflater layoutInflater;
private List<Integer> elementsPosArrayList = new ArrayList<>();
private HashMap<String, Integer> elementsMap = new HashMap<>();
public ShoppingListViewAdapter(Context context, Cursor c, int flags) {
super(context, c, flags);
layoutInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}
@Override
public View newView(Context context, Cursor cursor, ViewGroup viewGroup) {
return layoutInflater.inflate(R.layout.list_view_row, viewGroup, false);
}
@Override
public void bindView(View view, Context context, Cursor cursor) {
// CheckBox management
final CheckBox checkBoxElementName = view.findViewById(R.id.checkBoxElementName);
String elementName = cursor.getString(cursor.getColumnIndex(DBFieldsShoppingList.FIELD_ELEMENT_NAME));
checkBoxElementName.setText(elementName);
elementsMap.put(elementName, cursor.getPosition());
checkBoxElementName.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton compoundButton, boolean isChecked) {
if (isChecked) {
elementsPosArrayList.add(elementsMap.get(checkBoxElementName.getText().toString()));
} else {
elementsPosArrayList.remove(elementsMap.get(checkBoxElementName.getText().toString()));
}
}
});
}
public long getElementId(Cursor crs, int position) {
crs.moveToPosition(position);
return crs.getLong(crs.getColumnIndex(DBFieldsShoppingList.FIELD_ID));
}
public List<Integer> getElementsPosArrayList() {
return elementsPosArrayList;
}
}
Classes for the database management are the following: DBHelper:
public class DBHelperShoppingList extends SQLiteOpenHelper {
private String DBName;
public DBHelperShoppingList(@Nullable Context context, int dbVersion, String dbName) {
super(context, dbName, null, dbVersion);
this.DBName = dbName;
}
@Override
public void onCreate(SQLiteDatabase shoppingListDB) {
String q = "CREATE TABLE " + DBFieldsShoppingList.FIELD_TABLE_NAME +
" ( _id INTEGER PRIMARY KEY AUTOINCREMENT," +
DBFieldsShoppingList.FIELD_ELEMENT_NAME + " TEXT," +
DBFieldsShoppingList.FIELD_ELEMENT_TYPE + " TEXT," +
DBFieldsShoppingList.FIELD_ELEMENT_QUANT + " TEXT)";
shoppingListDB.execSQL(q);
}
@Override
public void onUpgrade(SQLiteDatabase shoppingListDB, int oldVersion, int newVersion) {}
}
Class for the fields of the database:
public class DBFieldsShoppingList {
public static final String FIELD_ID = "_Id";
public static final String FIELD_TABLE_NAME = "Shopping_List";
public static final String FIELD_ELEMENT_NAME = "Element_Name";
public static final String FIELD_ELEMENT_TYPE = "Element_Type";
public static final String FIELD_ELEMENT_QUANT = "Element_Quant";
}
Class database manager:
public class DBManagerShoppingList {
private DBHelperShoppingList dbHelperShoppingList;
public DBManagerShoppingList(Context ctx, String shoppingListName) {
dbHelperShoppingList = new DBHelperShoppingList(ctx, 1, shoppingListName);
}
public void dbSave(String elementName, String elementType, String elementQuantity) {
SQLiteDatabase db = dbHelperShoppingList.getWritableDatabase();
ContentValues cv = new ContentValues();
cv.put(DBFieldsShoppingList.FIELD_ELEMENT_NAME, elementName);
cv.put(DBFieldsShoppingList.FIELD_ELEMENT_TYPE, elementType);
cv.put(DBFieldsShoppingList.FIELD_ELEMENT_QUANT, elementQuantity);
try {
db.insert(DBFieldsShoppingList.FIELD_TABLE_NAME, null, cv);
} catch (SQLiteException ignored) {}
}
public boolean deleteElement(long id) {
SQLiteDatabase db = dbHelperShoppingList.getWritableDatabase();
try {
return db.delete(DBFieldsShoppingList.FIELD_TABLE_NAME, DBFieldsShoppingList.FIELD_ID + "=?", new String[]{Long.toString(id)})>0;
} catch(SQLiteException exc) {
return false;
}
}
public static void deleteDB(Context ctx, String DBName) {
ctx.deleteDatabase(DBName);
}
public Cursor query() {
Cursor crs;
try {
SQLiteDatabase db = dbHelperShoppingList.getReadableDatabase();
crs = db.query(DBFieldsShoppingList.FIELD_TABLE_NAME, null, null, null, null, null, null, null);
} catch (SQLiteException exc) {
return null;
}
return crs;
}
}
I tought, in bindView method of the adapter class, to save a map between element name and its position. Then, to create a list of the element names of the checked elements. In this way, I can know the positions of the checked elements, from the map. Now, I have to get indexes of the checked elements, in order to remove them from database, with delete method of the database manager class. How can I solve this problem? If my structure is not correct, say me how to change. Thank you very much in advance.
Marco
Hy to everybody, I found the solution. In database manager class, I changed the delete method in the following way:
public boolean deleteElement(String elementName) {
SQLiteDatabase db = dbHelperShoppingList.getWritableDatabase();
try {
return db.delete(DBFieldsShoppingList.FIELD_TABLE_NAME, DBFieldsShoppingList.FIELD_ELEMENT_NAME + "=?", new String[]{(elementName)})>0;
} catch(SQLiteException exc) {
return false;
}
}
This allows, to search by name in database. In adapter class, I removed the map, and I wrote an arraylist of string, where I put name of the checked elements:
@Override
public void bindView(View view, Context context, Cursor cursor) {
// CheckBox management
final CheckBox checkBoxElementName = view.findViewById(R.id.checkBoxElementName);
String elementName = cursor.getString(cursor.getColumnIndex(DBFieldsShoppingList.FIELD_ELEMENT_NAME));
checkBoxElementName.setText(elementName);
checkBoxElementName.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton compoundButton, boolean isChecked) {
if (isChecked) {
elementNamesArrayList.add(checkBoxElementName.getText().toString());
} else {
elementNamesArrayList.remove(checkBoxElementName.getText().toString());
}
}
});
}
Finally, in the activity class, the remove method is the following:
public void removeSelectedElements(View btnRemove) {
List<String> elementNamesArrayList = shoppingListViewAdapter.getElementNamesArrayList();
for (String item: elementNamesArrayList) {
dbShoppingList.deleteElement(item);
}
populateListView();
}
In this way I solved my problem.
Marco