如何在RecyclerView适配器中更新游标

Question

i built a RecyclerView Adapter which reads data out of a SQLite database. I have trouble updating the Adapter after the database were edited.

I know there are a few examples which show how to implement a swapCursor method into a RecyclerView Adapter, but they all contain a lot of additional code which i dont really know how to fit in. I feel like there is too little information about this out there.

In the following method i delete a database row depending on its position in the Adapter. When i call adapter.notifyItemRemoved(position) afterwards, it re-adds the item at the bottom. When i close and re-open the Activity, the database is correct. The problem is, that i dont swap the Cursor and i dont know how.

@Override
public void onDeleteClick(int position) {
    SQLiteDatabase database = new ExampleSQLiteHelper(this).getWritableDatabase();
    Cursor cursor = database.rawQuery("select * from " + ExampleContract.ExampleEntry.TABLE_NAME, null);
    cursor.moveToPosition(position);
    database.delete(ExampleContract.ExampleEntry.TABLE_NAME, ExampleContract.ExampleEntry._ID + "=?", new String[] {cursor.getString(cursor.getColumnIndexOrThrow(ExampleContract.ExampleEntry._ID))});
    //Here i have to swap the Cursor and notify the Adapter
}

1. How do i swap the Cursor properly and close the old one?
2. What Cursor do i have to provide? The one that queries the database for deletion is not up-to-date. So i would have to create a 2nd Cursor after deleting the row. That seems like a lot of Cursor creating and closing to me.
3. Is it ok to delete a row depending on its position in the Adapter, like i do in the above example? Since my ViewHolder Class is static, i cant access the Adapter's Cursor in there and can only get the Adapter position into the onClick method.

Edit:

Here is my approach for change the Cursor. It does work, but i dont know if its correct. Can anyone confirm this and are the Cursors closed prperly?

@Override
public void onDeleteClick(int position) {
    SQLiteDatabase database = new ExampleSQLiteHelper(this).getWritableDatabase();
    Cursor cursor = database.rawQuery("select * from " + ExampleContract.ExampleEntry.TABLE_NAME, null);
    cursor.moveToPosition(position);
    database.delete(ExampleContract.ExampleEntry.TABLE_NAME, ExampleContract.ExampleEntry._ID + "=?", new String[] {cursor.getString(cursor.getColumnIndexOrThrow(ExampleContract.ExampleEntry._ID))});
    cursor.close();

    Cursor newCursor = database.rawQuery("select * from " + ExampleContract.ExampleEntry.TABLE_NAME, null);
    mAdapter.changeCursor(newCursor);
    mAdapter.notifyItemRemoved(position);
}

Adapter:

public void changeCursor(Cursor newCursor) {
    Cursor oldCursor = mCursor;
    mCursor = newCursor;
    oldCursor.close();
}

Answer 1

That seems like a lot of Cursor creating and closing to me.

Well, without storing any extra data associated with the item you're deleting in the ViewHolder or adapter, you will need to perform a selection and extract the column. I would like to think adding a WHERE condition would benefit you, but moving to the necessary position is fine, in my opinion.

Since my ViewHolder Class is static, i cant access the Adapter's Cursor in there

I don't think you want the adapter cursor since it's already iterating the rows, but if your click method is defined onto the adapter class, you can get the cursor there. Otherwise adapter.this.cursor might work.

Regarding swapping the cursor, most examples you dismissed have that logic. Checkout , Using the recyclerview with a database