<分区>
我知道有很多主题或多或少相同的话题，但没有一个能涵盖我的情况:
我有一个删除按钮，可以删除 listView 中的一个项目，但是当您关闭应用程序并重新打开它时，这些项目会重新出现。我不知道如何解决这个问题。
DatabaseHelper.java
public class DatabaseHelper extends SQLiteOpenHelper {
public static final String DATABASE_NAME = "todo.db";
public static final int DATABASE_VERSION = 1;
public static final String ITEMS_TABLE = "items";
private static DatabaseHelper instance = null;
public static DatabaseHelper getInstance(Context context) {
if(instance == null) {
instance = new DatabaseHelper(context);
}
return instance;
}
private DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
String createQuery = "CREATE TABLE " + ITEMS_TABLE + " (" +
"_id INTEGER PRIMARY KEY AUTOINCREMENT," +
"description TEXT NOT NULL, " +
"completed INTEGER NOT NULL DEFAULT 0)";
db.execSQL(createQuery);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
}
该按钮工作正常，但它不会永久删除我不知道它是否是代码，或者它是否是我将它放在我的 MainActivity 中的位置，如果有人会告诉我会多赞赏。
MainActivity.java
public class MainActivity extends AppCompatActivity {
private static final String LOG_TAG = "ToDoApp";
private ToDoListManager listManager;
private ToDoItemAdapter adapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ListView todoList = (ListView) findViewById(R.id.todo_list);
listManager = new ToDoListManager(getApplicationContext());
adapter = new ToDoItemAdapter(
this,
listManager.getList()
);
todoList.setAdapter(adapter);
ImageButton addButton = (ImageButton) findViewById(R.id.add_item);
addButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
onAddButtonClick();
}
});
}
@Override
protected void onPause() {
super.onPause();
}
private void onAddButtonClick() {
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle(R.string.add_item);
final EditText input = new EditText(this);
input.setInputType(InputType.TYPE_CLASS_TEXT);
builder.setView(input);
builder.setPositiveButton(
R.string.ok,
new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
ToDoItem item = new ToDoItem(
input.getText().toString(),
false
);
listManager.addItem(item);
adapter.swapItems(listManager.getList());
}
});
builder.setNegativeButton(
R.string.cancel,
new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
dialog.cancel();
}
});
builder.show();
}
private class ToDoItemAdapter extends ArrayAdapter<ToDoItem> {
private Context context;
private List<ToDoItem> items;
private LayoutInflater inflater;
public ToDoItemAdapter(
Context context,
List<ToDoItem> items
) {
super(context, -1, items);
this.context = context;
this.items = items;
this.inflater = LayoutInflater.from(context);
}
public void swapItems(List<ToDoItem> items) {
this.items = items;
notifyDataSetChanged();
}
@Override
public int getCount() {
return items.size();
}
@Override
public View getView(final int position, View convertView, ViewGroup parent) {
final ItemViewHolder holder;
if(convertView == null) {
convertView = inflater.inflate(R.layout.to_do_item_layout, parent, false);
holder = new ItemViewHolder();
holder.itemDescription = (TextView) convertView.findViewById(R.id.item);
holder.itemState = (CheckBox) convertView.findViewById(R.id.checkBox);
convertView.setTag(holder);
}else {
holder = (ItemViewHolder) convertView.getTag();
}
holder.itemDescription.setText(items.get(position).getDescription());
holder.itemState.setChecked(items.get(position).isComplete());
holder.itemState.setTag(items.get(position));
convertView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
ToDoItem item = (ToDoItem) holder.itemState.getTag();
item.toggleComplete();
listManager.updateItem(item);
notifyDataSetChanged();
}
});
ImageButton deleteButton = (ImageButton) convertView.findViewById(R.id.delete_Button);
deleteButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
items.remove(items.get(position));
notifyDataSetChanged();
}
});
holder.itemState.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
ToDoItem item = (ToDoItem) holder.itemState.getTag();
item.toggleComplete();
listManager.updateItem(item);
notifyDataSetChanged();
}
});
return convertView;
}
}
public static class ItemViewHolder{
public TextView itemDescription;
public CheckBox itemState;
}
}
ToDoListManager.java
public class ToDoListManager {
private DatabaseHelper dbHelper;
public ToDoListManager(Context context) {
dbHelper = DatabaseHelper.getInstance(context);
}
public List<ToDoItem> getList() {
SQLiteDatabase db = dbHelper.getReadableDatabase();
Cursor cursor = db.rawQuery(
"SELECT * FROM " + DatabaseHelper.ITEMS_TABLE,
null
);
List<ToDoItem> items = new ArrayList<>();
if(cursor.moveToFirst()) {
while(!cursor.isAfterLast()) {
ToDoItem item = new ToDoItem(
cursor.getString(cursor.getColumnIndex("description")),
cursor.getInt(cursor.getColumnIndex("completed")) != 0,
cursor.getLong(cursor.getColumnIndex("_id"))
);
items.add(item);
cursor.moveToNext();
}
}
cursor.close();
return items;
}
public void addItem(ToDoItem item) {
ContentValues newItem = new ContentValues();
newItem.put("description", item.getDescription());
newItem.put("completed", item.isComplete());
SQLiteDatabase db = dbHelper.getWritableDatabase();
db.insert(DatabaseHelper.ITEMS_TABLE, null, newItem);
}
public void updateItem(ToDoItem item) {
ContentValues editItem = new ContentValues();
editItem.put("description", item.getDescription());
editItem.put("completed", item.isComplete());
SQLiteDatabase db = dbHelper.getWritableDatabase();
String[] args = new String[] { String.valueOf(item.getId()) };
db.update(DatabaseHelper.ITEMS_TABLE, editItem, "_id=?", args);
}
}
ToDoItem.java
public class ToDoItem {
private String description;
private boolean isComplete;
private long id;
public ToDoItem(String description, boolean isComplete) {
this(description, isComplete, -1);
}
public ToDoItem(String description,boolean isComplete,long id) {
this.description = description;
this.isComplete = isComplete;
this.id = id;
}
public String getDescription() {
return description;
}
public boolean isComplete() {
return isComplete;
}
public void toggleComplete() {
isComplete = !isComplete;
}
public long getId() {return id;}
@Override
public String toString() {
return getDescription();
}
}