使用 RecyclerView 和 Fragments 检索数据库信息

Question

1. 如何使用“getCategories()”检索 CategoryListFragment 中的数据？ 我在 MyDBHelper 中有 GetAllValues() 函数，但不确定如何使用它@fragments 类，因为尝试时无法正确初始化 MyDBHelper 对象。

MyDBHelper.class

public class MyDatabaseHelper extends SQLiteOpenHelper {

private static final String DATABASE_NAME="CategoryDatabase";

public MyDatabaseHelper(Context context) {

    super(context, DATABASE_NAME, null, 1);

}

@Override

public void onCreate(SQLiteDatabase database) {

    database.execSQL("CREATE TABLE Category (_id INTEGER PRIMARY KEY AUTOINCREMENT, name TEXT);");

}

@Override

public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    db.execSQL("DROP TABLE IF EXISTS Category");

    onCreate(db);

}

public void addCategory(String name)

{

    ContentValues values=new ContentValues(1);

    values.put("name", name);

    getWritableDatabase().insert("Category", "name", values);

}

public Cursor getCategories()

{

    Cursor cursor = getReadableDatabase().rawQuery("select * from Category", null);

    return cursor;

}

public ArrayList<String> GetAllValues()
{
    String aTable = "Category"; // Table's name
    ArrayList<String> list = new ArrayList<String>();
    Cursor cursor =  getCategories();
    if (cursor.moveToFirst())
    {
        do
        {
            list.add(cursor.getString(0));
        }
        while (cursor.moveToNext());
    }
    if (cursor != null && !cursor.isClosed())
    {
        cursor.close();
    }

    return list;
}
}

Answer 1

在你的片段类中像这样初始化 MyDatabaseHelper 对象

MyDatabaseHelper dbHelper = new MyDatabaseHelper(getActivity()); 

然后在 getCategories 方法中像这样获取它

ArrayList<String> list = dbHelper.GetAllValues();

编辑：

public ArrayList<String> GetAllValues()
{
String aTable = "Category"; // Table's name
ArrayList<Category> list = new ArrayList<>();
Cursor cursor =  getCategories();
if (cursor.moveToFirst())
{
    do
    {
       Category cat  = new Category(cursor.getString(0));
        list.add(cat);
    }
    while (cursor.moveToNext());
}
if (cursor != null && !cursor.isClosed())
{
    cursor.close();
}

return list;
}

编辑 2： 尝试添加这样的片段

getSupportFragmentManager().beginTransaction().replace(R.id.test_container, fragment, "CategoryFragment").commit();