android - 如何将 SQLite 数据库中的数据显示到 RecyclerView
问题描述
我想将我的 SQLite 数据库中的数据显示到我的 RecyclerView(使用 LinearLayoutManager)。我为列表创建了 RecyclerView 布局,并为单个项目创建了 CardView 布局。我用配方表创建了数据库,我可以保存一个新的配方。我的目标是在 CardView 中显示食谱的标题。
食谱类
public class Recipe {
private int id;
private String title;
private String photo;
private String instructions;
private int targetPeople;
private int time;
public Recipe() {
this.id = id;
this.title = title;
this.photo = photo;
this.instructions = instructions;
this.targetPeople = targetPeople;
this.time = time;
}
(加上 setter/getter 方法)
在 DatabaseHelper 中,我创建了一个方法来将所有食谱添加到列表中:
public List<Recipe> getAllRecipes() {
// sorting orders
String sortOrder =
RECIPE_TITLE + " ASC";
List<Recipe> recipeList = new ArrayList<Recipe>();
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery("SELECT * FROM " + TBL_RECIPE, null);
// Traversing through all rows and adding to list
if (cursor.moveToFirst()) {
do {
Recipe recipe = new Recipe();
recipe.setTitle(cursor.getString(cursor.getColumnIndex("TITLE")));
// Adding user record to list
recipeList.add(recipe);
} while (cursor.moveToNext());
}
cursor.close();
db.close();
// return user list
return recipeList;
}
这是我的适配器类和 RecyclerView 的 ViewHolder 类:
public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {
private Context mContext;
private List<Recipe> recipeList;
//constructor of adapter
public MyAdapter(Context mContext, List<Recipe> recipeList) {
this.mContext = mContext;
this.recipeList = recipeList;
}
//ViewHolder Class
public class ViewHolder extends RecyclerView.ViewHolder {
public final TextView textViewTitle;
//constructor for ViewHolder
public ViewHolder(View itemView) {
super(itemView);
textViewTitle = itemView.findViewById(R.id.descriptionView);
}
}
//return an instance of ViewHolder Class
@NonNull
@Override
public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int position) {
View itemView = LayoutInflater.from(parent.getContext())
.inflate(R.layout.list_item_card, parent, false);
return new ViewHolder(itemView);
}
//binding data to our ViewHolder
@Override
public void onBindViewHolder(@NonNull ViewHolder viewHolder, int position) {
// retrieve UI elements inside viewHolder object
viewHolder.textViewTitle.setText(recipeList.get(position).getTitle());
}
//return the size of the list
@Override
public int getItemCount() {
return recipeList.size();
}
}
最后,我在 MainActivity 中声明了 RecyclerView、List、Adapter 等,在这里我创建了一个显示所有 Recipes 的方法:
@SuppressLint("StaticFieldLeak")
private void displayAllRecipes() {
// AsyncTask is used that SQLite operation does not block the UI Thread.
new AsyncTask<Void, Void, ArrayList<Recipe>>() {
@Override
protected ArrayList<Recipe> doInBackground(Void... params) {
recipeList.clear();
recipeList.addAll(dbHelper. getAllRecipes());
return recipeList;
}
@Override
protected void onPostExecute(ArrayList<Recipe> aVoid) {
super.onPostExecute(aVoid);
resultAdapter.notifyDataSetChanged();
}
}.execute();
}
没有错误,但它不起作用。
解决方案
确保您已将 arrayList 传递给适配器并将适配器设置为 recyclerView。
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