Android 如何删除SQL数据库中的项?
我知道有很多帖子或多或少都有相同的主题,但没有一个能涵盖我的情况: 我有一个删除按钮,可以删除列表视图中的一个项目,但当你关闭应用程序并重新打开它时,项目会重新出现。我不知道怎么解决这个问题 DatabaseHelper.javaAndroid 如何删除SQL数据库中的项?,android,listview,android-studio,delete-row,Android,Listview,Android Studio,Delete Row,我知道有很多帖子或多或少都有相同的主题,但没有一个能涵盖我的情况: 我有一个删除按钮,可以删除列表视图中的一个项目,但当你关闭应用程序并重新打开它时,项目会重新出现。我不知道怎么解决这个问题 DatabaseHelper.java public class DatabaseHelper extends SQLiteOpenHelper { public static final String DATABASE_NAME = "todo.db"; public static final int D
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) {
}
}
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;
}
}
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);
}
}
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();
}
}
该按钮工作正常,但不会永久删除。我不知道它是否是代码,或者它是否在我的MainActivity
中放置的位置。如果有人告诉我,我将不胜感激
MainActivity.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) {
}
}
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;
}
}
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);
}
}
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();
}
}
您只需删除适配器类中导致该项从当前listView中删除的项。但是,您的
topolistmanager.java
中没有任何函数可以从数据库中删除项目。从listView中删除不会影响对数据库项的访问
您可以将此函数添加到ToDoListManager.java
类中
public void deleteItem(long itemId) {
SQLiteDatabase db = dbHelper.getWritableDatabase();
db.delete(DatabaseHelper.ITEMS_TABLE, "_id = ?",
new String[] { String.valueOf(itemId) });
}
从删除按钮的onClick调用它,如下所示
ImageButton deleteButton = (ImageButton) convertView.findViewById(R.id.delete_Button);
deleteButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
long itemId = items.get(position).getId();
items.remove(items.get(position));
listManager.deleteItem(itemId);
notifyDataSetChanged();
}
});
由于要从数据库中获取数据并在listview中显示,所以也需要从数据库中删除该行。在数据库适配器中创建一个如下所示的方法:
public boolean deleteItem(Long id) {
return Db.delete(DATABASE_TABLE,"_id="+id,null) > 0;
}
然后在list view item delete上,只需调用此方法并将行id作为参数传递。我是新手,您能告诉我在哪里添加这段代码吗?在您的数据库帮助器类中,就像您的onCreate()和onUpgrade()方法一样。我按照您所说的做了,它说无法解析items listManager.deleteItem(item.getId());我编辑了我的答案。请重试
listManager.deleteItem(item.getId())代码>无法解决此问题,因为在onclick
scopeitem
中未知,这是我的第一个答案中的打字错误,您需要在scope中使用items
列表感谢您的出色回答,它将发挥您的最佳效果!我只是想知道我是否可以在你的帮助下添加更多的功能?我想在列表中添加项目的时间戳。你们认为你们能帮忙吗?我很高兴,我认为最好再问一个问题,把你们新问题的链接放在这里,我会在这里回答你们。如果这个答案有效,也请接受。