我已经实现了显示虚拟卡的CardView。但我不得不 从SQLite数据库向这些卡显示数据，即从每行到 每张卡片。此外，我想在卡中按下删除按钮时删除特定行。我怎么能这样做？
这是我的卡片段代码：
public class UserAppFragment extends Fragment {
public UserAppFragment() {
// Required empty public constructor
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
//using recycle view cutomizing card views
RecyclerView recyclerView = (RecyclerView) inflater.inflate(
R.layout.recycler_view, container, false);
ContentAdapter adapter = new ContentAdapter();
recyclerView.setAdapter(adapter);
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
FloatingActionButton fab = (FloatingActionButton) getActivity().findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
// Click action
Toast.makeText(getContext(),"FAB",Toast.LENGTH_SHORT).show();
Intent intent = new Intent(getContext(), EventAdder.class);
startActivity(intent);
}
});
return recyclerView;
}
//view holder for cards data start
public static class ViewHolder extends RecyclerView.ViewHolder {
public ViewHolder(LayoutInflater inflater, ViewGroup parent) {
super(inflater.inflate(R.layout.fragment_home_card_list, parent, false));
itemView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Context context = v.getContext();
Intent intent = new Intent(context, EventAdder.class);
context.startActivity(intent);
}
});
ImageButton shareImageButton =
(ImageButton) itemView.findViewById(R.id.share_button);
shareImageButton.setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View v) {
Snackbar.make(v, "Added to Favorite",
Snackbar.LENGTH_LONG).show();
}
});
ImageButton deleteImageButton = (ImageButton) itemView.findViewById(R.id.delete_button);
deleteImageButton.setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View v) {
Snackbar.make(v, "Card deleted",
Snackbar.LENGTH_LONG).show();
}
});
}
} //view holder end
// start recycleview.adapter wrapping viewholder created
public static class ContentAdapter extends RecyclerView.Adapter<ViewHolder> {
// Set numbers of List in RecyclerView.
private static final int LENGTH = 15;
public ContentAdapter(){
}
@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
return new ViewHolder(LayoutInflater.from(parent.getContext()), parent);
}
@Override
public void onBindViewHolder(ViewHolder holder, int position) {
// no-op
}
@Override
public int getItemCount() {
return LENGTH;
}
}
// end recycleview.adapter wrapping viewholder created
@Override
public void onDetach() {
super.onDetach();
}
}
答案 0 :(得分：4)
遵循这些步骤：
1）使用DB Helper为您的应用程序创建sqlite数据库。
示例：
public class FeedReaderDbHelper extends SQLiteOpenHelper {
// If you change the database schema, you must increment the database version.
public static final int DATABASE_VERSION = 1;
public static final String DATABASE_NAME = "FeedReader.db";
public FeedReaderDbHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
public void onCreate(SQLiteDatabase db) {
db.execSQL(SQL_CREATE_ENTRIES);
}
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// This database is only a cache for online data, so its upgrade policy is
// to simply to discard the data and start over
db.execSQL(SQL_DELETE_ENTRIES);
onCreate(db);
}
public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) {
onUpgrade(db, oldVersion, newVersion);
}
}
要访问上述课程：
FeedReaderDbHelper mDbHelper = new FeedReaderDbHelper(getContext());
2）您需要在数据库中插入数据。重要的是，您必须在表格中包含 id 列。
// Gets the data repository in write mode
SQLiteDatabase db = mDbHelper.getWritableDatabase();
// Create a new map of values, where column names are the keys
ContentValues values = new ContentValues();
values.put(FeedEntry.COLUMN_NAME_ENTRY_ID, id);
values.put(FeedEntry.COLUMN_NAME_TITLE, title);
values.put(FeedEntry.COLUMN_NAME_CONTENT, content);
// Insert the new row, returning the primary key value of the new row
long newRowId;
newRowId = db.insert(
FeedEntry.TABLE_NAME,
FeedEntry.COLUMN_NAME_NULLABLE,
values);
现在，您的数据库中有数据。 （您也可以使用以下POJO类，在表格中插入数据）
3）创建 POJO对象以从数据库中获取数据。
public class Example{
int id;
String title;
String content;
public Example() {
}
public Example(int id, String title, String content) {
this.id = id;
this.title = title;
this.content = content;
}
}
4）以List<Example>。
SQLiteDatabase db = mDbHelper.getReadableDatabase();
String selectQuery = "SELECT * FROM yourTableName";
Cursor c = database.rawQuery(selectQuery, null);
List<Example> example = new ArrayList<Example>();
if (cursor.moveToFirst()) {
do {
example.add(new Example(
c.getInt(0), // id
c.getString(1), // title
c.getString(2) // content
));
} while (cursor.moveToNext());
}
5）在RecyclerView的 onBindViewHolder 方法中获取数据列表List<Example> example，并使用UI参考设置数据。也在这里设置onClickListener
@Override
public void onBindViewHolder(ViewHolder holder, int position) {
Example temp = example.get(position);
holder.tvTitle.setText(temp.title);
holder.tvContent.setText(temp.content);
holder.deleteImageButton.setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View v) {
// Define 'where' part of query.
String selection = FeedEntry.COLUMN_NAME_ENTRY_ID + " LIKE ?";
// Specify arguments in placeholder order.
String[] selectionArgs = { String.valueOf(temp.id) };
// Issue SQL statement.
db.delete(table_name, selection, selectionArgs);
// delete item from list
example.remove(temp);
// adapter must be in global scope.
adapter.notifyDataSetChanged();
Snackbar.make(v, "Card deleted",
Snackbar.LENGTH_LONG).show();
}
});
}
希望这可以帮助您或尝试观看一些视频以获得更多说明。
答案 1 :(得分：0)
使用此方法获取数据库的上下文参数
public void onBindViewHolder(ViewHolder holder,final int position) {
CardView cardView = holder.cardView;
Context context = cardView.getContext();
YoupostDatabase youpostDatabase = new YoupostDatabase(context);
SQLiteDatabase db = youpostDatabase.getReadableDatabase();
}