我正在构建一个使用SQLite进行持久化的应用程序，并且还包含一个CursorAdapter。我可以将项添加到ListView和SQLite表中，并可以在应用程序重启时查看这些项。我再次重新启动后，我也能够删除项目并查看更改。我添加了一个带onClickListener的编辑功能，一旦我点击某个项目，它就会带我进入编辑界面，我可以编辑该特定项目。这就是我所拥有的：
Mainactivity.java
public class MainActivity extends AppCompatActivity {
DatabaseHelper databaseHelper;
private final int REQUEST_CODE = 10;
ArrayList <String> toDoItems;
ArrayAdapter<String> adapter;
SimpleCursorAdapter altAdapter;
Cursor itemListCursor;
ListView listItems;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
listItems = (ListView) findViewById(R.id.listViewItems);
toDoItems = new ArrayList<>();
adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, toDoItems);
databaseHelper = new DatabaseHelper(this);
getItemListAsCursor();
altAdapter = new SimpleCursorAdapter(
this,
android.R.layout.simple_list_item_1,
itemListCursor,
new String[]{TO_DO},
new int[]{android.R.id.text1},
0);
listItems.setAdapter(altAdapter);
listItems.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
@Override
public boolean onItemLongClick(AdapterView<?> adapter, View item, int position, long id) {
itemDeleteFromDatabase(id);
getItemListAsCursor();
altAdapter.swapCursor(itemListCursor);
return true;
}
});
listItems.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> adapter, View item, int pos, long id) {
Intent intent = new Intent(MainActivity.this, EditItemActivity.class);
intent.putExtra("itemName", toDoItems.get(pos));
intent.putExtra("itemPos", id);
startActivityForResult(intent, REQUEST_CODE);
}
});
}
@Override
protected void onDestroy() {
super.onDestroy();
itemListCursor.close();
}
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
if (resultCode == RESULT_OK && requestCode == REQUEST_CODE) {
String item = data.getStringExtra("item");
int itemPosition = Integer.parseInt(data.getStringExtra("itemPos"));
toDoItems.add(itemPosition, item);
databaseHelper.insertData(item);
toDoItems.remove(itemPosition + 1);
itemDeleteFromDatabase((long) (itemPosition + 1));
adapter.notifyDataSetChanged();
}
}
public void addItem(View v) {
EditText newItem = (EditText) findViewById(R.id.itemInputEditText);
if (newItem.getText().length() == 0) {
Toast.makeText(this, "You need to enter a to do.", Toast.LENGTH_SHORT).show();
} else {
String item = newItem.getText().toString();
databaseHelper.insertData(item);
getItemListAsCursor();
altAdapter.swapCursor(itemListCursor);
adapter.notifyDataSetChanged();
newItem.setText("");
}
}
public void getToDos(){
SQLiteDatabase database = databaseHelper.getWritableDatabase();
Cursor cursor = database.rawQuery("select * from student",null);
if (cursor.moveToFirst()) {
while (!cursor.isAfterLast()) {
String name = cursor.getString(cursor.getColumnIndex("todo"));
adapter.add(name);
adapter.notifyDataSetChanged();
cursor.moveToNext();
}
}
}
public void getItemListAsCursor() {
SQLiteDatabase database = databaseHelper.getWritableDatabase();
itemListCursor = database.query(TABLE_NAME,null,null,null,null,null,null);
}
public boolean itemDeleteFromDatabase(Long id) {
SQLiteDatabase database = databaseHelper.getWritableDatabase();
boolean databaseDelete = database.delete(TABLE_NAME, ID + "=?", new String[]{Long.toString(id)}) > 0;
return databaseDelete;
}
}
EditItemActivity.java
public class EditItemActivity extends AppCompatActivity {
EditText editToDo;
Long itemPos;
Button saveChanges;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_edit_item);
editToDo = (EditText) findViewById(R.id.edit_todo_item);
saveChanges = (Button)findViewById(R.id.save_changes);
String itemName = getIntent().getStringExtra("itemName");
editToDo.setText(itemName);
itemPos = getIntent().getLongExtra("itemPos", 0);
saveChanges.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
onSubmit();
}
});
}
public void onSubmit() {
Intent item = new Intent();
item.putExtra("itemName", editToDo.getText().toString());
item.putExtra("itemPos", itemPos);
setResult(RESULT_OK, item);
finish();
}
}
但是当我点击某个项目时，我会得到臭名昭着的indexOutOfBounds异常。这是堆栈跟踪：
FATAL EXCEPTION: main
Process: ca.ozbek.preworktodoapp, PID: 13721
java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
at java.util.ArrayList.get(ArrayList.java:411)
at ca.ozbek.preworktodoapp.MainActivity$2.onItemClick(MainActivity.java:65)
我知道因为我使用的是CursorAdapter，我应该在我的id和intent.putExtra("item", toDoItems.get(pos));代码行中使用intent.putExtra("itemPos", String.valueOf(pos));而不是pos但我不能这样做是因为id是一个很长的值。
答案 0 :(得分：1)
如果您创建DBHelper类生命，则可以非常轻松地处理所有CRUD函数 所以你的列表有一个位置，你的记录有一个ID，当你点击btnDelete时你正在使用的活动使用这样的代码
// Calls the Method deleteDBRow in DatabaseHelper
// which acts on the TABLE_INFO to remove a record by getting the record ID
helper.deleteDBRow(String.valueOf(dbList.get(position).getID()));
ListActivity.removeListRow(position);
//上面的代码行调用ListActivity中的方法来通知Recycler视图的更改 //注意列表按位置保存项目而不是ID＆lt; == READ
现在确定你的DBHelper类实现了下面的方法代码
/* Delete a record from database table named "TABLE_INFO" */
/* based on the selected records id in Col_ID*/
public void deleteDBRow(String rowid){
db = this.getWritableDatabase();
db.delete(TABLE_INFO, Col_ID + " = ?", new String[] { rowid });
db.close();
return;
}