[英]SQLite in Android - How to refresh the list
我正在制作酒單應用程序。 我也在嘗試在其中使用 SQLite,我很難掌握它。
我有很多活動,但現在有兩個與此相關。
我目前遇到的問題是,當我將葡萄酒添加到列表中時,當我回到 MainActivity 時,列表不會顯示新添加的 Wine,直到我關閉應用程序並返回它。
我該如何解決?
這是我的主要方法:
public class MainActivity extends AppCompatActivity {
DatabaseHelper mDatabaseHelper;
ListView listView;
ArrayAdapter adapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent intentGoToAdd = new Intent(MainActivity.this, AddActivity.class);
startActivity(intentGoToAdd);
}
});
mDatabaseHelper = new DatabaseHelper(this);
arrayListAndAdapter();
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long l) {
SQLiteDatabase db = mDatabaseHelper.getReadableDatabase();
//Which columns I want to select
String[] projection = {
WineContract.WineEntry.COLUMN_ID,
WineContract.WineEntry.COLUMN_WINE_NAME,
WineContract.WineEntry.COLUMN_WINE_PRICE,
WineContract.WineEntry.COLUMN_WINE_DESCRIPTION};
Cursor cursor = db.query(WineContract.WineEntry.TABLE_NAME, projection,null,null,null,null,null);
cursor.moveToPosition(position);
Intent intentGoToDetails = new Intent(MainActivity.this,DetailsActivity.class);
String name = cursor.getString(cursor.getColumnIndex(WineContract.WineEntry.COLUMN_WINE_NAME));
String price = cursor.getString(cursor.getColumnIndex(WineContract.WineEntry.COLUMN_WINE_PRICE));
String description = cursor.getString(cursor.getColumnIndex(WineContract.WineEntry.COLUMN_WINE_DESCRIPTION));
intentGoToDetails.putExtra("NAME", name);
intentGoToDetails.putExtra("PRICE", price);
intentGoToDetails.putExtra("DESCRIPTION", description);
startActivity(intentGoToDetails);
}
});
}
@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_deleteDB) {
mDatabaseHelper.deleteDatabase();
return true;
}
return super.onOptionsItemSelected(item);
}
public void arrayListAndAdapter(){
SQLiteDatabase db = mDatabaseHelper.getReadableDatabase();
//Which columns I want to select
String[] projection = {
WineContract.WineEntry.COLUMN_ID,
WineContract.WineEntry.COLUMN_WINE_NAME,
WineContract.WineEntry.COLUMN_WINE_PRICE,
WineContract.WineEntry.COLUMN_WINE_DESCRIPTION};
Cursor cursor = db.query(WineContract.WineEntry.TABLE_NAME, projection,null,null,null,null,null);
ArrayList<String> mArrayList = new ArrayList<String>();
while(cursor.moveToNext()) {
mArrayList.add(cursor.getString(cursor.getColumnIndex(WineContract.WineEntry.COLUMN_WINE_NAME))); //add the item
}
listView = (ListView) findViewById(R.id.list);
adapter = new ArrayAdapter(MainActivity.this, android.R.layout.simple_list_item_1, mArrayList);
listView.setAdapter(adapter);
}
}
這是添加活動:
public class AddActivity extends AppCompatActivity {
EditText editWineName, editWinePrice, editWineDescription;
DatabaseHelper mDatabaseHelper;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_add);
mDatabaseHelper = new DatabaseHelper(this);
editWineName = (EditText) findViewById(R.id.editWineName);
editWinePrice = (EditText) findViewById(R.id.editWinePrice);
editWineDescription = (EditText) findViewById(R.id.editWineDescription);
}
public void toastMessage(String message){
Toast.makeText(this, message, Toast.LENGTH_SHORT).show();
}
@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_add, 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_deleteDB) {
long result = mDatabaseHelper.addWine(editWineName.getText().toString(), editWinePrice.getText().toString(), editWineDescription.getText().toString() );
if (result!=-1){
toastMessage(editWineName.getText().toString() + " was added to the list.");
finish();
}else{
toastMessage("Error");
}
return true;
}
return super.onOptionsItemSelected(item);
}
}
如有必要,這是我的 DatabaseHelper 類:
public class DatabaseHelper extends SQLiteOpenHelper {
private static final int DATABASE_VERSION = 1;
private static final String DATABASE_NAME = "wines.db";
private static final String SQL_CREATE =
"CREATE TABLE IF NOT EXISTS " + TABLE_NAME + " (" +
COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
COLUMN_WINE_NAME + " TEXT, " +
COLUMN_WINE_PRICE + " TEXT, " +
COLUMN_WINE_DESCRIPTION + " TEXT);";
public DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(SQL_CREATE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
onCreate(db);
}
public long addWine(String name, String price, String description){
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(COLUMN_WINE_NAME, name);
values.put(COLUMN_WINE_PRICE, price);
values.put(COLUMN_WINE_DESCRIPTION, description);
return db.insert(TABLE_NAME,null, values);
}
public void deleteDatabase(){
SQLiteDatabase db = this.getWritableDatabase();
db.delete(TABLE_NAME,null,null);
}
}
您的活動僅創建一次,因此 onCreate 僅在第一次被調用。 您想要的是每次 MainActivity 恢復時數據都是新鮮的。 如果您覆蓋 onResume 方法並放置您的 arrayListAndAdapter() 方法和 setOnItemClickListener,您將獲得所需的效果。 所以這是新代碼(您也可以從 onCreate 中刪除此代碼以防止查詢兩次):
@Override
protected void onResume() {
super.onResume();
arrayListAndAdapter();
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long l) {
SQLiteDatabase db = mDatabaseHelper.getReadableDatabase();
//Which columns I want to select
String[] projection = {
WineContract.WineEntry.COLUMN_ID,
WineContract.WineEntry.COLUMN_WINE_NAME,
WineContract.WineEntry.COLUMN_WINE_PRICE,
WineContract.WineEntry.COLUMN_WINE_DESCRIPTION};
Cursor cursor = db.query(WineContract.WineEntry.TABLE_NAME, projection,null,null,null,null,null);
cursor.moveToPosition(position);
Intent intentGoToDetails = new Intent(MainActivity.this,DetailsActivity.class);
String name = cursor.getString(cursor.getColumnIndex(WineContract.WineEntry.COLUMN_WINE_NAME));
String price = cursor.getString(cursor.getColumnIndex(WineContract.WineEntry.COLUMN_WINE_PRICE));
String description = cursor.getString(cursor.getColumnIndex(WineContract.WineEntry.COLUMN_WINE_DESCRIPTION));
intentGoToDetails.putExtra("NAME", name);
intentGoToDetails.putExtra("PRICE", price);
intentGoToDetails.putExtra("DESCRIPTION", description);
startActivity(intentGoToDetails);
}
});
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